Under memory pressure, we sometimes observe the following crash:
[ 5694.832838] ------------[ cut here ]------------
[ 5694.842093] list_del corruption, ffff888014b6a448->next is LIST_POISON1 (dead000000000100)
[ 5694.858677] WARNING: CPU: 33 PID: 418824 at lib/list_debug.c:47 __list_del_entry_valid+0x42/0x80
[ 5694.961820] CPU: 33 PID: 418824 Comm: fuse_counters.s Kdump: loaded Tainted: G S 5.19.0-0_fbk3_rc3_hoangnhatpzsdynshrv41_10870_g85a9558a25de #1
[ 5694.990194] Hardware name: Wiwynn Twin Lakes MP/Twin Lakes Passive MP, BIOS YMM16 05/24/2021
[ 5695.007072] RIP: 0010:__list_del_entry_valid+0x42/0x80
[ 5695.017351] Code: 08 48 83 c2 22 48 39 d0 74 24 48 8b 10 48 39 f2 75 2c 48 8b 51 08 b0 01 48 39 f2 75 34 c3 48 c7 c7 55 d7 78 82 e8 4e 45 3b 00 <0f> 0b eb 31 48 c7 c7 27 a8 70 82 e8 3e 45 3b 00 0f 0b eb 21 48 c7
[ 5695.054919] RSP: 0018:ffffc90027aef4f0 EFLAGS: 00010246
[ 5695.065366] RAX: 41fe484987275300 RBX: ffff888008988180 RCX: 0000000000000000
[ 5695.079636] RDX: ffff88886006c280 RSI: ffff888860060480 RDI: ffff888860060480
[ 5695.093904] RBP: 0000000000000002 R08: 0000000000000000 R09: ffffc90027aef370
[ 5695.108175] R10: 0000000000000000 R11: ffffffff82fdf1c0 R12: 0000000010000002
[ 5695.122447] R13: ffff888014b6a448 R14: ffff888014b6a420 R15: 00000000138dc240
[ 5695.136717] FS: 00007f23a7d3f740(0000) GS:ffff888860040000(0000) knlGS:0000000000000000
[ 5695.152899] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5695.164388] CR2: 0000560ceaab6ac0 CR3: 000000001c06c001 CR4: 00000000007706e0
[ 5695.178659] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 5695.192927] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 5695.207197] PKRU: 55555554
[ 5695.212602] Call Trace:
[ 5695.217486] <TASK>
[ 5695.221674] zs_map_object+0x91/0x270
[ 5695.229000] zswap_frontswap_store+0x33d/0x870
[ 5695.237885] ? do_raw_spin_lock+0x5d/0xa0
[ 5695.245899] __frontswap_store+0x51/0xb0
[ 5695.253742] swap_writepage+0x3c/0x60
[ 5695.261063] shrink_page_list+0x738/0x1230
[ 5695.269255] shrink_lruvec+0x5ec/0xcd0
[ 5695.276749] ? shrink_slab+0x187/0x5f0
[ 5695.284240] ? mem_cgroup_iter+0x6e/0x120
[ 5695.292255] shrink_node+0x293/0x7b0
[ 5695.299402] do_try_to_free_pages+0xea/0x550
[ 5695.307940] try_to_free_pages+0x19a/0x490
[ 5695.316126] __folio_alloc+0x19ff/0x3e40
[ 5695.323971] ? __filemap_get_folio+0x8a/0x4e0
[ 5695.332681] ? walk_component+0x2a8/0xb50
[ 5695.340697] ? generic_permission+0xda/0x2a0
[ 5695.349231] ? __filemap_get_folio+0x8a/0x4e0
[ 5695.357940] ? walk_component+0x2a8/0xb50
[ 5695.365955] vma_alloc_folio+0x10e/0x570
[ 5695.373796] ? walk_component+0x52/0xb50
[ 5695.381634] wp_page_copy+0x38c/0xc10
[ 5695.388953] ? filename_lookup+0x378/0xbc0
[ 5695.397140] handle_mm_fault+0x87f/0x1800
[ 5695.405157] do_user_addr_fault+0x1bd/0x570
[ 5695.413520] exc_page_fault+0x5d/0x110
[ 5695.421017] asm_exc_page_fault+0x22/0x30
After some investigation, I have found the following issue: unlike other
zswap backends, zsmalloc performs the LRU list update at the object
mapping time, rather than when the slot for the object is allocated.
This deviation was discussed and agreed upon during the review process
of the zsmalloc writeback patch series:
https://lore.kernel.org/lkml/Y3flcAXNxxrvy3ZH@cmpxchg.org/
Unfortunately, this introduces a subtle bug that occurs when there is a
concurrent store and reclaim, which interleave as follows:
zswap_frontswap_store() shrink_worker()
zs_malloc() zs_zpool_shrink()
spin_lock(&pool->lock) zs_reclaim_page()
zspage = find_get_zspage()
spin_unlock(&pool->lock)
spin_lock(&pool->lock)
zspage = list_first_entry(&pool->lru)
list_del(&zspage->lru)
zspage->lru.next = LIST_POISON1
zspage->lru.prev = LIST_POISON2
spin_unlock(&pool->lock)
zs_map_object()
spin_lock(&pool->lock)
if (!list_empty(&zspage->lru))
list_del(&zspage->lru)
CHECK_DATA_CORRUPTION(next == LIST_POISON1) /* BOOM */
With the current upstream code, this issue rarely happens. zswap only
triggers writeback when the pool is already full, at which point all
further store attempts are short-circuited. This creates an implicit
pseudo-serialization between reclaim and store. I am working on a new
zswap shrinking mechanism, which makes interleaving reclaim and store
more likely, exposing this bug.
zbud and z3fold do not have this problem, because they perform the LRU
list update in the alloc function, while still holding the pool's lock.
This patch fixes the aforementioned bug by moving the LRU update back to
zs_malloc(), analogous to zbud and z3fold.
Link: https://lkml.kernel.org/r/20230505185054.2417128-1-nphamcs@gmail.com
Fixes: 64f768c6b3 ("zsmalloc: add a LRU to zs_pool to keep track of zspages in LRU order")
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc pool can be compacted concurrently by many contexts,
e.g.
cc1 handle_mm_fault()
do_anonymous_page()
__alloc_pages_slowpath()
try_to_free_pages()
do_try_to_free_pages(
lru_gen_shrink_node()
shrink_slab()
do_shrink_slab()
zs_shrinker_scan()
zs_compact()
Pool compaction is currently (basically) single-threaded as
it is performed under pool->lock. Having multiple compaction
threads results in unnecessary contention, as each thread
competes for pool->lock. This, in turn, affects all zsmalloc
operations such as zs_malloc(), zs_map_object(), zs_free(), etc.
Introduce the pool->compaction_in_progress atomic variable,
which ensures that only one compaction context can run at a
time. This reduces overall pool->lock contention in (corner)
cases when many contexts attempt to shrink zspool simultaneously.
Link: https://lkml.kernel.org/r/20230418074639.1903197-1-senozhatsky@chromium.org
Fixes: c0547d0b6a ("zsmalloc: consolidate zs_pool's migrate_lock and size_class's locks")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The current implementation of the compaction loop fails to set the source
zspage pointer to NULL in all cases, leading to a potential issue where
__zs_compact() could use a stale zspage pointer. This pointer could even
point to a previously freed zspage, causing unexpected behavior in the
putback_zspage() and migrate_write_unlock() functions after returning from
the compaction loop.
Address the issue by ensuring that the source zspage pointer is always set
to NULL when it should be.
Link: https://lkml.kernel.org/r/20230417130850.1784777-1-senozhatsky@chromium.org
Fixes: 5a845e9f2d ("zsmalloc: rework compaction algorithm")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reported-by: Yu Zhao <yuzhao@google.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
We keep the old fullness (3/4 threshold) reporting in
zs_stats_size_show(). Switch from allmost full/empty stats to
fine-grained per inuse ratio (fullness group) reporting, which gives
signicantly more data on classes fragmentation.
Link: https://lkml.kernel.org/r/20230304034835.2082479-5-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The zsmalloc compaction algorithm has the potential to waste some CPU
cycles, particularly when compacting pages within the same fullness group.
This is due to the way it selects the head page of the fullness list for
source and destination pages, and how it reinserts those pages during each
iteration. The algorithm may first use a page as a migration destination
and then as a migration source, leading to an unnecessary back-and-forth
movement of objects.
Consider the following fullness list:
PageA PageB PageC PageD PageE
During the first iteration, the compaction algorithm will select PageA as
the source and PageB as the destination. All of PageA's objects will be
moved to PageB, and then PageA will be released while PageB is reinserted
into the fullness list.
PageB PageC PageD PageE
During the next iteration, the compaction algorithm will again select the
head of the list as the source and destination, meaning that PageB will
now serve as the source and PageC as the destination. This will result in
the objects being moved away from PageB, the same objects that were just
moved to PageB in the previous iteration.
To prevent this avalanche effect, the compaction algorithm should not
reinsert the destination page between iterations. By doing so, the most
optimal page will continue to be used and its usage ratio will increase,
reducing internal fragmentation. The destination page should only be
reinserted into the fullness list if:
- It becomes full
- No source page is available.
TEST
====
It's very challenging to reliably test this series. I ended up developing
my own synthetic test that has 100% reproducibility. The test generates
significan fragmentation (for each size class) and then performs
compaction for each class individually and tracks the number of memcpy()
in zs_object_copy(), so that we can compare the amount work compaction
does on per-class basis.
Total amount of work (zram mm_stat objs_moved)
----------------------------------------------
Old fullness grouping, old compaction algorithm:
323977 memcpy() in zs_object_copy().
Old fullness grouping, new compaction algorithm:
262944 memcpy() in zs_object_copy().
New fullness grouping, new compaction algorithm:
213978 memcpy() in zs_object_copy().
Per-class compaction memcpy() comparison (T-test)
-------------------------------------------------
x Old fullness grouping, old compaction algorithm
+ Old fullness grouping, new compaction algorithm
N Min Max Median Avg Stddev
x 140 349 3513 2461 2314.1214 806.03271
+ 140 289 2778 2006 1878.1714 641.02073
Difference at 95.0% confidence
-435.95 +/- 170.595
-18.8387% +/- 7.37193%
(Student's t, pooled s = 728.216)
x Old fullness grouping, old compaction algorithm
+ New fullness grouping, new compaction algorithm
N Min Max Median Avg Stddev
x 140 349 3513 2461 2314.1214 806.03271
+ 140 226 2279 1644 1528.4143 524.85268
Difference at 95.0% confidence
-785.707 +/- 159.331
-33.9527% +/- 6.88516%
(Student's t, pooled s = 680.132)
Link: https://lkml.kernel.org/r/20230304034835.2082479-4-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Each zspage maintains ->inuse counter which keeps track of the number of
objects stored in the zspage. The ->inuse counter also determines the
zspage's "fullness group" which is calculated as the ratio of the "inuse"
objects to the total number of objects the zspage can hold
(objs_per_zspage). The closer the ->inuse counter is to objs_per_zspage,
the better.
Each size class maintains several fullness lists, that keep track of
zspages of particular "fullness". Pages within each fullness list are
stored in random order with regard to the ->inuse counter. This is
because sorting the zspages by ->inuse counter each time obj_malloc() or
obj_free() is called would be too expensive. However, the ->inuse counter
is still a crucial factor in many situations.
For the two major zsmalloc operations, zs_malloc() and zs_compact(), we
typically select the head zspage from the corresponding fullness list as
the best candidate zspage. However, this assumption is not always
accurate.
For the zs_malloc() operation, the optimal candidate zspage should have
the highest ->inuse counter. This is because the goal is to maximize the
number of ZS_FULL zspages and make full use of all allocated memory.
For the zs_compact() operation, the optimal source zspage should have the
lowest ->inuse counter. This is because compaction needs to move objects
in use to another page before it can release the zspage and return its
physical pages to the buddy allocator. The fewer objects in use, the
quicker compaction can release the zspage. Additionally, compaction is
measured by the number of pages it releases.
This patch reworks the fullness grouping mechanism. Instead of having two
groups - ZS_ALMOST_EMPTY (usage ratio below 3/4) and ZS_ALMOST_FULL (usage
ration above 3/4) - that result in too many zspages being included in the
ALMOST_EMPTY group for specific classes, size classes maintain a larger
number of fullness lists that give strict guarantees on the minimum and
maximum ->inuse values within each group. Each group represents a 10%
change in the ->inuse ratio compared to neighboring groups. In essence,
there are groups for zspages with 0%, 10%, 20% usage ratios, and so on, up
to 100%.
This enhances the selection of candidate zspages for both zs_malloc() and
zs_compact(). A printout of the ->inuse counters of the first 7 zspages
per (random) class fullness group:
class-768 objs_per_zspage 16:
fullness 100%: empty
fullness 99%: empty
fullness 90%: empty
fullness 80%: empty
fullness 70%: empty
fullness 60%: 8 8 9 9 8 8 8
fullness 50%: empty
fullness 40%: 5 5 6 5 5 5 5
fullness 30%: 4 4 4 4 4 4 4
fullness 20%: 2 3 2 3 3 2 2
fullness 10%: 1 1 1 1 1 1 1
fullness 0%: empty
The zs_malloc() function searches through the groups of pages starting
with the one having the highest usage ratio. This means that it always
selects a zspage from the group with the least internal fragmentation
(highest usage ratio) and makes it even less fragmented by increasing its
usage ratio.
The zs_compact() function, on the other hand, begins by scanning the group
with the highest fragmentation (lowest usage ratio) to locate the source
page. The first available zspage is selected, and then the function moves
downward to find a destination zspage in the group with the lowest
internal fragmentation (highest usage ratio).
Link: https://lkml.kernel.org/r/20230304034835.2082479-3-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "zsmalloc: fine-grained fullness and new compaction
algorithm", v4.
Existing zsmalloc page fullness grouping leads to suboptimal page
selection for both zs_malloc() and zs_compact(). This patchset reworks
zsmalloc fullness grouping/classification.
Additinally it also implements new compaction algorithm that is expected
to use less CPU-cycles (as it potentially does fewer memcpy-s in
zs_object_copy()).
Test (synthetic) results can be seen in patch 0003.
This patch (of 4):
This optimization has no effect. It only ensures that when a zspage was
added to its corresponding fullness list, its "inuse" counter was higher
or lower than the "inuse" counter of the zspage at the head of the list.
The intention was to keep busy zspages at the head, so they could be
filled up and moved to the ZS_FULL fullness group more quickly. However,
this doesn't work as the "inuse" counter of a zspage can be modified by
obj_free() but the zspage may still belong to the same fullness list. So,
fix_fullness_group() won't change the zspage's position in relation to the
head's "inuse" counter, leading to a largely random order of zspages
within the fullness list.
For instance, consider a printout of the "inuse" counters of the first 10
zspages in a class that holds 93 objects per zspage:
ZS_ALMOST_EMPTY: 36 67 68 64 35 54 63 52
As we can see the zspage with the lowest "inuse" counter
is actually the head of the fullness list.
Remove this pointless "optimisation".
Link: https://lkml.kernel.org/r/20230304034835.2082479-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20230304034835.2082479-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Remove hard coded limit on the maximum number of physical pages
per-zspage.
This will allow tuning of zsmalloc pool as zspage chain size changes
`pages per-zspage` and `objects per-zspage` characteristics of size
classes which also affects size classes clustering (the way size classes
are merged).
Link: https://lkml.kernel.org/r/20230118005210.2814763-4-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
If a class size is power of 2 then it wastes no memory and the best
configuration is 1 physical page per-zspage.
Link: https://lkml.kernel.org/r/20230118005210.2814763-3-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "zsmalloc: make zspage chain size configurable".
Computers are bad at division. We currently decide the best zspage chain
size (max number of physical pages per-zspage) by looking at a `used
percentage` value. This is not enough as we lose precision during usage
percentage calculations For example, let's look at size class 208:
pages per zspage wasted bytes used%
1 144 96
2 80 99
3 16 99
4 160 99
Current algorithm will select 2 page per zspage configuration, as it's the
first one to reach 99%. However, 3 pages per zspage waste less memory.
Change algorithm and select zspage configuration that has lowest wasted
value.
Link: https://lkml.kernel.org/r/20230118005210.2814763-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20230118005210.2814763-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently, there is a race between zs_free() and zs_reclaim_page():
zs_reclaim_page() finds a handle to an allocated object, but before the
eviction happens, an independent zs_free() call to the same handle could
come in and overwrite the object value stored at the handle with the last
deferred handle. When zs_reclaim_page() finally gets to call the eviction
handler, it will see an invalid object value (i.e the previous deferred
handle instead of the original object value).
This race happens quite infrequently. We only managed to produce it with
out-of-tree developmental code that triggers zsmalloc writeback with a
much higher frequency than usual.
This patch fixes this race by storing the deferred handle in the object
header instead. We differentiate the deferred handle from the other two
cases (handle for allocated object, and linkage for free object) with a
new tag. If zspage reclamation succeeds, we will free these deferred
handles by walking through the zspage objects. On the other hand, if
zspage reclamation fails, we reconstruct the zspage freelist (with the
deferred handle tag and allocated tag) before trying again with the
reclamation.
[arnd@arndb.de: avoid unused-function warning]
Link: https://lkml.kernel.org/r/20230117170507.2651972-1-arnd@kernel.org
Link: https://lkml.kernel.org/r/20230110231701.326724-1-nphamcs@gmail.com
Fixes: 9997bc0175 ("zsmalloc: implement writeback mechanism for zsmalloc")
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The only in-kernel users that need PageMovable() to be exported are z3fold
and zsmalloc and they are only using it for dubious debugging
functionality. So remove those usages and the export so that no driver
code accidentally thinks that they are allowed to use this symbol.
Link: https://lkml.kernel.org/r/20230106135900.3763622-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit adds the writeback mechanism for zsmalloc, analogous to the
zbud allocator. Zsmalloc will attempt to determine the coldest zspage
(i.e least recently used) in the pool, and attempt to write back all the
stored compressed objects via the pool's evict handler.
Link: https://lkml.kernel.org/r/20221128191616.1261026-7-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This adds a new field to zs_pool to store evict handlers for writeback,
analogous to the zbud allocator.
Link: https://lkml.kernel.org/r/20221128191616.1261026-6-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently, zsmalloc has a hierarchy of locks, which includes a pool-level
migrate_lock, and a lock for each size class. We have to obtain both
locks in the hotpath in most cases anyway, except for zs_malloc. This
exception will no longer exist when we introduce a LRU into the zs_pool
for the new writeback functionality - we will need to obtain a pool-level
lock to synchronize LRU handling even in zs_malloc.
In preparation for zsmalloc writeback, consolidate these locks into a
single pool-level lock, which drastically reduces the complexity of
synchronization in zsmalloc.
We have also benchmarked the lock consolidation to see the performance
effect of this change on zram.
First, we ran a synthetic FS workload on a server machine with 36 cores
(same machine for all runs), using
fs_mark -d ../zram1mnt -s 100000 -n 2500 -t 32 -k
before and after for btrfs and ext4 on zram (FS usage is 80%).
Here is the result (unit is file/second):
With lock consolidation (btrfs):
Average: 13520.2, Median: 13531.0, Stddev: 137.5961482019028
Without lock consolidation (btrfs):
Average: 13487.2, Median: 13575.0, Stddev: 309.08283679298665
With lock consolidation (ext4):
Average: 16824.4, Median: 16839.0, Stddev: 89.97388510006668
Without lock consolidation (ext4)
Average: 16958.0, Median: 16986.0, Stddev: 194.7370021336469
As you can see, we observe a 0.3% regression for btrfs, and a 0.9%
regression for ext4. This is a small, barely measurable difference in my
opinion.
For a more realistic scenario, we also tries building the kernel on zram.
Here is the time it takes (in seconds):
With lock consolidation (btrfs):
real
Average: 319.6, Median: 320.0, Stddev: 0.8944271909999159
user
Average: 6894.2, Median: 6895.0, Stddev: 25.528415540334656
sys
Average: 521.4, Median: 522.0, Stddev: 1.51657508881031
Without lock consolidation (btrfs):
real
Average: 319.8, Median: 320.0, Stddev: 0.8366600265340756
user
Average: 6896.6, Median: 6899.0, Stddev: 16.04057355583023
sys
Average: 520.6, Median: 521.0, Stddev: 1.140175425099138
With lock consolidation (ext4):
real
Average: 320.0, Median: 319.0, Stddev: 1.4142135623730951
user
Average: 6896.8, Median: 6878.0, Stddev: 28.621670111997307
sys
Average: 521.2, Median: 521.0, Stddev: 1.7888543819998317
Without lock consolidation (ext4)
real
Average: 319.6, Median: 319.0, Stddev: 0.8944271909999159
user
Average: 6886.2, Median: 6887.0, Stddev: 16.93221781102523
sys
Average: 520.4, Median: 520.0, Stddev: 1.140175425099138
The difference is entirely within the noise of a typical run on zram.
This hardly justifies the complexity of maintaining both the pool lock and
the class lock. In fact, for writeback, we would need to introduce yet
another lock to prevent data races on the pool's LRU, further complicating
the lock handling logic. IMHO, it is just better to collapse all of these
into a single pool-level lock.
Link: https://lkml.kernel.org/r/20221128191616.1261026-4-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
It makes no sense for us to recompress the object if it will be in the
same size class. We anyway don't get any memory gain. But, at the same
time, we get a CPU time overhead when inserting this object into zspage
and decompressing it afterwards.
[senozhatsky: rebased and fixed conflicts]
Link: https://lkml.kernel.org/r/20221109115047.2921851-9-senozhatsky@chromium.org
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Inside the zs_destroy_pool() function, there can still be NULL size_class
pointers: if when the next size_class is allocated, inside
zs_create_pool() function, kzalloc will return NULL and handling the error
condition, zs_create_pool() will call zs_destroy_pool().
Link: https://lkml.kernel.org/r/20221013112825.61869-1-avromanov@sberdevices.ru
Fixes: f24263a5a0 ("zsmalloc: remove unnecessary size_class NULL check")
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Since commit ffedd09fa9 ("zsmalloc: Stop using slab fields in struct
page") we are using page->page_type (unsigned int) field instead of
page->units (int) as first object offset in a subpage of zspage. So
get_first_obj_offset() and set_first_obj_offset() functions should work
with unsigned int type.
Link: https://lkml.kernel.org/r/20220909083722.85024-1-avromanov@sberdevices.ru
Fixes: ffedd09fa9 ("zsmalloc: Stop using slab fields in struct page")
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
pool->size_class array elements can't be NULL, so this check
is not needed.
In the whole code, we assign pool->size_class[i] values that are
not NULL. Releasing memory for these values occurs in the
zs_destroy_pool() function, which also releases and destroys the pool.
In addition, in the zs_stats_size_show() and async_free_zspage(),
with similar iterations over the array, we don't check it for NULL
pointer.
Link: https://lkml.kernel.org/r/20220811153755.16102-3-avromanov@sberdevices.ru
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "tidy up zsmalloc implementation"
This patchset remove some unnecessary checks and adds a clarifying
comment. While analysing zs_object_copy() function code, I spent some
time to understand what the call kunmap_atomic(d_addr) is for. It seems
that this point is not trivial and it is worth adding a comment.
This patch (of 2):
It's not obvious why kunmap_atomic(d_addr) call is needed.
[akpm@linux-foundation.org: tweak comment layout]
Link: https://lkml.kernel.org/r/20220811153755.16102-1-avromanov@sberdevices.ru
Link: https://lkml.kernel.org/r/20220811153755.16102-2-avromanov@sberdevices.ru
Signed-off-by: Alexey Romanov <avromanov@sberdevices.ru>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zsmalloc() now returns ERR_PTR values as handles, which zram accidentally
can pass to zs_free(). Another bad scenario is when zcomp_compress()
fails - handle has default -ENOMEM value, and zs_free() will try to free
that "pointer value".
Add the missing check and make sure that zs_free() bails out when
ERR_PTR() is passed to it.
Link: https://lkml.kernel.org/r/20220816050906.2583956-1-senozhatsky@chromium.org
Fixes: c7e6f17b52 ("zsmalloc: zs_malloc: return ERR_PTR on failure")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>,
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lin, Yang Shi, Anshuman Khandual and Mike Rapoport
- Some kmemleak fixes from Patrick Wang and Waiman Long
- DAMON updates from SeongJae Park
- memcg debug/visibility work from Roman Gushchin
- vmalloc speedup from Uladzislau Rezki
- more folio conversion work from Matthew Wilcox
- enhancements for coherent device memory mapping from Alex Sierra
- addition of shared pages tracking and CoW support for fsdax, from
Shiyang Ruan
- hugetlb optimizations from Mike Kravetz
- Mel Gorman has contributed some pagealloc changes to improve latency
and realtime behaviour.
- mprotect soft-dirty checking has been improved by Peter Xu
- Many other singleton patches all over the place
-----BEGIN PGP SIGNATURE-----
iHUEABYKAB0WIQTTMBEPP41GrTpTJgfdBJ7gKXxAjgUCYuravgAKCRDdBJ7gKXxA
jpqSAQDrXSdII+ht9kSHlaCVYjqRFQz/rRvURQrWQV74f6aeiAD+NHHeDPwZn11/
SPktqEUrF1pxnGQxqLh1kUFUhsVZQgE=
=w/UH
-----END PGP SIGNATURE-----
Merge tag 'mm-stable-2022-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull MM updates from Andrew Morton:
"Most of the MM queue. A few things are still pending.
Liam's maple tree rework didn't make it. This has resulted in a few
other minor patch series being held over for next time.
Multi-gen LRU still isn't merged as we were waiting for mapletree to
stabilize. The current plan is to merge MGLRU into -mm soon and to
later reintroduce mapletree, with a view to hopefully getting both
into 6.1-rc1.
Summary:
- The usual batches of cleanups from Baoquan He, Muchun Song, Miaohe
Lin, Yang Shi, Anshuman Khandual and Mike Rapoport
- Some kmemleak fixes from Patrick Wang and Waiman Long
- DAMON updates from SeongJae Park
- memcg debug/visibility work from Roman Gushchin
- vmalloc speedup from Uladzislau Rezki
- more folio conversion work from Matthew Wilcox
- enhancements for coherent device memory mapping from Alex Sierra
- addition of shared pages tracking and CoW support for fsdax, from
Shiyang Ruan
- hugetlb optimizations from Mike Kravetz
- Mel Gorman has contributed some pagealloc changes to improve
latency and realtime behaviour.
- mprotect soft-dirty checking has been improved by Peter Xu
- Many other singleton patches all over the place"
[ XFS merge from hell as per Darrick Wong in
https://lore.kernel.org/all/YshKnxb4VwXycPO8@magnolia/ ]
* tag 'mm-stable-2022-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (282 commits)
tools/testing/selftests/vm/hmm-tests.c: fix build
mm: Kconfig: fix typo
mm: memory-failure: convert to pr_fmt()
mm: use is_zone_movable_page() helper
hugetlbfs: fix inaccurate comment in hugetlbfs_statfs()
hugetlbfs: cleanup some comments in inode.c
hugetlbfs: remove unneeded header file
hugetlbfs: remove unneeded hugetlbfs_ops forward declaration
hugetlbfs: use helper macro SZ_1{K,M}
mm: cleanup is_highmem()
mm/hmm: add a test for cross device private faults
selftests: add soft-dirty into run_vmtests.sh
selftests: soft-dirty: add test for mprotect
mm/mprotect: fix soft-dirty check in can_change_pte_writable()
mm: memcontrol: fix potential oom_lock recursion deadlock
mm/gup.c: fix formatting in check_and_migrate_movable_page()
xfs: fail dax mount if reflink is enabled on a partition
mm/memcontrol.c: remove the redundant updating of stats_flush_threshold
userfaultfd: don't fail on unrecognized features
hugetlb_cgroup: fix wrong hugetlb cgroup numa stat
...
These drivers are rather uncomfortably hammered into the
address_space_operations hole. They aren't filesystems and don't behave
like filesystems. They just need their own movable_operations structure,
which we can point to directly from page->mapping.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
zs_malloc returns 0 if it fails. zs_zpool_malloc will return -1 when
zs_malloc return 0. But -1 makes the return value unclear.
For example, when zswap_frontswap_store calls zs_malloc through
zs_zpool_malloc, it will return -1 to its caller. The other return value
is -EINVAL, -ENODEV or something else.
This commit changes zs_malloc to return ERR_PTR on failure. It didn't
just let zs_zpool_malloc return -ENOMEM becaue zs_malloc has two types of
failure:
- size is not OK return -EINVAL
- memory alloc fail return -ENOMEM.
Link: https://lkml.kernel.org/r/20220714080757.12161-1-teawater@gmail.com
Signed-off-by: Hui Zhu <teawater@antgroup.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently shrinkers are anonymous objects. For debugging purposes they
can be identified by count/scan function names, but it's not always
useful: e.g. for superblock's shrinkers it's nice to have at least an
idea of to which superblock the shrinker belongs.
This commit adds names to shrinkers. register_shrinker() and
prealloc_shrinker() functions are extended to take a format and arguments
to master a name.
In some cases it's not possible to determine a good name at the time when
a shrinker is allocated. For such cases shrinker_debugfs_rename() is
provided.
The expected format is:
<subsystem>-<shrinker_type>[:<instance>]-<id>
For some shrinkers an instance can be encoded as (MAJOR:MINOR) pair.
After this change the shrinker debugfs directory looks like:
$ cd /sys/kernel/debug/shrinker/
$ ls
dquota-cache-16 sb-devpts-28 sb-proc-47 sb-tmpfs-42
mm-shadow-18 sb-devtmpfs-5 sb-proc-48 sb-tmpfs-43
mm-zspool:zram0-34 sb-hugetlbfs-17 sb-pstore-31 sb-tmpfs-44
rcu-kfree-0 sb-hugetlbfs-33 sb-rootfs-2 sb-tmpfs-49
sb-aio-20 sb-iomem-12 sb-securityfs-6 sb-tracefs-13
sb-anon_inodefs-15 sb-mqueue-21 sb-selinuxfs-22 sb-xfs:vda1-36
sb-bdev-3 sb-nsfs-4 sb-sockfs-8 sb-zsmalloc-19
sb-bpf-32 sb-pipefs-14 sb-sysfs-26 thp-deferred_split-10
sb-btrfs:vda2-24 sb-proc-25 sb-tmpfs-1 thp-zero-9
sb-cgroup2-30 sb-proc-39 sb-tmpfs-27 xfs-buf:vda1-37
sb-configfs-23 sb-proc-41 sb-tmpfs-29 xfs-inodegc:vda1-38
sb-dax-11 sb-proc-45 sb-tmpfs-35
sb-debugfs-7 sb-proc-46 sb-tmpfs-40
[roman.gushchin@linux.dev: fix build warnings]
Link: https://lkml.kernel.org/r/Yr+ZTnLb9lJk6fJO@castle
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lkml.kernel.org/r/20220601032227.4076670-4-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The asynchronous zspage free worker tries to lock a zspage's entire page
list without defending against page migration. Since pages which haven't
yet been locked can concurrently migrate off the zspage page list while
lock_zspage() churns away, lock_zspage() can suffer from a few different
lethal races.
It can lock a page which no longer belongs to the zspage and unsafely
dereference page_private(), it can unsafely dereference a torn pointer to
the next page (since there's a data race), and it can observe a spurious
NULL pointer to the next page and thus not lock all of the zspage's pages
(since a single page migration will reconstruct the entire page list, and
create_page_chain() unconditionally zeroes out each list pointer in the
process).
Fix the races by using migrate_read_lock() in lock_zspage() to synchronize
with page migration.
Link: https://lkml.kernel.org/r/20220509024703.243847-1-sultan@kerneltoast.com
Fixes: 77ff465799 ("zsmalloc: zs_page_migrate: skip unnecessary loops but not return -EBUSY if zspage is not inuse")
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The usage of get_cpu_var() in zs_map_object() is problematic because it
disables preemption and makes it impossible to acquire any sleeping lock
on PREEMPT_RT such as a spinlock_t.
Replace the get_cpu_var() usage with a local_lock_t which is embedded
struct mapping_area. It ensures that the access the struct is
synchronized against all users on the same CPU.
[minchan: remove the bit_spin_lock part and change the title]
Link: https://lkml.kernel.org/r/20211115185909.3949505-10-minchan@kernel.org
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The zsmalloc has used a bit for spin_lock in zpage handle to keep zpage
object alive during several operations. However, it causes the problem
for PREEMPT_RT as well as introducing too complicated.
This patch replaces the bit spin_lock with pool->migrate_lock rwlock.
It could make the code simple as well as zsmalloc work under PREEMPT_RT.
The drawback is the pool->migrate_lock is bigger granuarity than per
zpage lock so the contention would be higher than old when both
IO-related operations(i.e., zsmalloc, zsfree, zs_[map|unmap]) and
compaction(page/zpage migration) are going in parallel(*, the
migrate_lock is rwlock and IO related functions are all read side lock
so there is no contention). However, the write-side is fast
enough(dominant overhead is just page copy) so it wouldn't affect much.
If the lock granurity becomes more problem later, we could introduce
table locks based on handle as a hash value.
Link: https://lkml.kernel.org/r/20211115185909.3949505-9-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
zspage isolation for migration introduced additional exceptions to be
dealt with since the zspage was isolated from class list. The reason
why I isolated zspage from class list was to prevent race between
obj_malloc and page migration via allocating zpage from the zspage
further. However, it couldn't prevent object freeing from zspage so it
needed corner case handling.
This patch removes the whole mess. Now, we are fine since class->lock
and zspage->lock can prevent the race.
Link: https://lkml.kernel.org/r/20211115185909.3949505-7-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The flag aims for zspage, not per page. Let's move it to zspage.
Link: https://lkml.kernel.org/r/20211115185909.3949505-6-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The usage pattern for obj_to_head is to check whether the zpage is
allocated or not. Thus, introduce obj_allocated.
Link: https://lkml.kernel.org/r/20211115185909.3949505-5-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This patch moves class stat update out of obj_malloc since it's not
related to zspage operation. This is a preparation to introduce new
lock scheme in next patch.
Link: https://lkml.kernel.org/r/20211115185909.3949505-4-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The stat aims for class stat, not zspage so rename it.
Link: https://lkml.kernel.org/r/20211115185909.3949505-3-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "zsmalloc: remove bit_spin_lock", v2.
zsmalloc uses bit_spin_lock to minimize space overhead since it's zpage
granularity lock. However, it causes zsmalloc non-working under
PREEMPT_RT as well as adding too much complication.
This patchset tries to replace the bit_spin_lock with per-pool rwlock.
It also removes unnecessary zspage isolation logic from class, which was
the other part too much complication added into zsmalloc.
Last patch changes the get_cpu_var to local_lock to make it work in
PREEMPT_RT.
This patch (of 9):
get_zspage_mapping returns fullness as well as class_idx. However, the
fullness is usually not used since it could be stale in some contexts.
It causes misleading as well as unnecessary instructions so this patch
introduces zspage_class.
obj_to_location also produces page and index but we don't need always
the index, either so this patch introduces obj_to_page.
Link: https://lkml.kernel.org/r/20211115185909.3949505-1-minchan@kernel.org
Link: https://lkml.kernel.org/r/20211115185909.3949505-2-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The ->freelist and ->units members of struct page are for the use of
slab only. I'm not particularly familiar with zsmalloc, so generate the
same code by using page->index to store 'page' (page->index and
page->freelist are at the same offset in struct page). This should be
cleaned up properly at some point by somebody who is familiar with
zsmalloc.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
There is one possible race window between zs_pool_dec_isolated() and
zs_unregister_migration() because wait_for_isolated_drain() checks the
isolated count without holding class->lock and there is no order inside
zs_pool_dec_isolated(). Thus the below race window could be possible:
zs_pool_dec_isolated zs_unregister_migration
check pool->destroying != 0
pool->destroying = true;
smp_mb();
wait_for_isolated_drain()
wait for pool->isolated_pages == 0
atomic_long_dec(&pool->isolated_pages);
atomic_long_read(&pool->isolated_pages) == 0
Since we observe the pool->destroying (false) before atomic_long_dec()
for pool->isolated_pages, waking pool->migration_wait up is missed.
Fix this by ensure checking pool->destroying happens after the
atomic_long_dec(&pool->isolated_pages).
Link: https://lkml.kernel.org/r/20210708115027.7557-1-linmiaohe@huawei.com
Fixes: 701d678599 ("mm/zsmalloc.c: fix race condition in zs_destroy_pool")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Henry Burns <henryburns@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The class is extracted from pool->size_class[class_idx] again before
calling __free_zspage(). It looks like class will change after we fetch
the class lock. But this is misleading as class will stay unchanged.
Link: https://lkml.kernel.org/r/20210624123930.1769093-4-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "Cleanup for zsmalloc".
This series contains cleanups to remove confusing code in obj_free(),
combine two atomic ops and improve readability for async_free_zspage().
More details can be found in the respective changelogs.
This patch (of 2):
OBJ_ALLOCATED_TAG is only set for handle to indicate allocated object.
It's irrelevant with obj. So remove this misleading code to improve
readability.
Link: https://lkml.kernel.org/r/20210624123930.1769093-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20210624123930.1769093-2-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It can be optimized at compile time.
Link: https://lkml.kernel.org/r/1616727798-9110-1-git-send-email-zhouchuangao@vivo.com
Signed-off-by: zhouchuangao <zhouchuangao@vivo.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It's recommended to use helper macro page_private() to access the private
field of page. Use such helper to eliminate direct access.
Link: https://lkml.kernel.org/r/20210203091857.20017-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There exists multiple path may do zram compaction concurrently.
1. auto-compaction triggered during memory reclaim
2. userspace utils write zram<id>/compaction node
So, multiple threads may call zs_shrinker_scan/zs_compact concurrently.
But pages_compacted is a per zsmalloc pool variable and modification
of the variable is not serialized(through under class->lock).
There are two issues here:
1. the pages_compacted may not equal to total number of pages
freed(due to concurrently add).
2. zs_shrinker_scan may not return the correct number of pages
freed(issued by current shrinker).
The fix is simple:
1. account the number of pages freed in zs_compact locally.
2. use actomic variable pages_compacted to accumulate total number.
Link: https://lkml.kernel.org/r/20210202122235.26885-1-wu-yan@tcl.com
Fixes: 860c707dca ("zsmalloc: account the number of compacted pages")
Signed-off-by: Rokudo Yan <wu-yan@tcl.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We always memset the zspage allocated via cache_alloc_zspage. So it's
more convenient to use kmem_cache_zalloc in cache_alloc_zspage than caller
do it manually.
Link: https://lkml.kernel.org/r/20210114120032.25885-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rework the list_add code to make it more readable and simple.
Link: https://lkml.kernel.org/r/20201015130107.65195-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
While I was doing zram testing, I found sometimes decompression failed
since the compression buffer was corrupted. With investigation, I found
below commit calls cond_resched unconditionally so it could make a
problem in atomic context if the task is reschedule.
BUG: sleeping function called from invalid context at mm/vmalloc.c:108
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 946, name: memhog
3 locks held by memhog/946:
#0: ffff9d01d4b193e8 (&mm->mmap_lock#2){++++}-{4:4}, at: __mm_populate+0x103/0x160
#1: ffffffffa3d53de0 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0xa98/0x1160
#2: ffff9d01d56b8110 (&zspage->lock){.+.+}-{3:3}, at: zs_map_object+0x8e/0x1f0
CPU: 0 PID: 946 Comm: memhog Not tainted 5.9.3-00011-gc5bfc0287345-dirty #316
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
Call Trace:
unmap_kernel_range_noflush+0x2eb/0x350
unmap_kernel_range+0x14/0x30
zs_unmap_object+0xd5/0xe0
zram_bvec_rw.isra.0+0x38c/0x8e0
zram_rw_page+0x90/0x101
bdev_write_page+0x92/0xe0
__swap_writepage+0x94/0x4a0
pageout+0xe3/0x3a0
shrink_page_list+0xb94/0xd60
shrink_inactive_list+0x158/0x460
We can fix this by removing the ZSMALLOC_PGTABLE_MAPPING feature (which
contains the offending calling code) from zsmalloc.
Even though this option showed some amount improvement(e.g., 30%) in
some arm32 platforms, it has been headache to maintain since it have
abused APIs[1](e.g., unmap_kernel_range in atomic context).
Since we are approaching to deprecate 32bit machines and already made
the config option available for only builtin build since v5.8, lastly it
has been not default option in zsmalloc, it's time to drop the option
for better maintenance.
[1] http://lore.kernel.org/linux-mm/20201105170249.387069-1-minchan@kernel.org
Fixes: e47110e905 ("mm/vunmap: add cond_resched() in vunmap_pmd_range")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Harish Sriram <harish@linux.ibm.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201117202916.GA3856507@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
