linux/mm/damon/vaddr.c
Ryan Roberts c33c794828 mm: ptep_get() conversion
Convert all instances of direct pte_t* dereferencing to instead use
ptep_get() helper.  This means that by default, the accesses change from a
C dereference to a READ_ONCE().  This is technically the correct thing to
do since where pgtables are modified by HW (for access/dirty) they are
volatile and therefore we should always ensure READ_ONCE() semantics.

But more importantly, by always using the helper, it can be overridden by
the architecture to fully encapsulate the contents of the pte.  Arch code
is deliberately not converted, as the arch code knows best.  It is
intended that arch code (arm64) will override the default with its own
implementation that can (e.g.) hide certain bits from the core code, or
determine young/dirty status by mixing in state from another source.

Conversion was done using Coccinelle:

----

// $ make coccicheck \
//          COCCI=ptepget.cocci \
//          SPFLAGS="--include-headers" \
//          MODE=patch

virtual patch

@ depends on patch @
pte_t *v;
@@

- *v
+ ptep_get(v)

----

Then reviewed and hand-edited to avoid multiple unnecessary calls to
ptep_get(), instead opting to store the result of a single call in a
variable, where it is correct to do so.  This aims to negate any cost of
READ_ONCE() and will benefit arch-overrides that may be more complex.

Included is a fix for an issue in an earlier version of this patch that
was pointed out by kernel test robot.  The issue arose because config
MMU=n elides definition of the ptep helper functions, including
ptep_get().  HUGETLB_PAGE=n configs still define a simple
huge_ptep_clear_flush() for linking purposes, which dereferences the ptep.
So when both configs are disabled, this caused a build error because
ptep_get() is not defined.  Fix by continuing to do a direct dereference
when MMU=n.  This is safe because for this config the arch code cannot be
trying to virtualize the ptes because none of the ptep helpers are
defined.

Link: https://lkml.kernel.org/r/20230612151545.3317766-4-ryan.roberts@arm.com
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202305120142.yXsNEo6H-lkp@intel.com/
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-06-19 16:19:25 -07:00

720 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* DAMON Primitives for Virtual Address Spaces
*
* Author: SeongJae Park <sjpark@amazon.de>
*/
#define pr_fmt(fmt) "damon-va: " fmt
#include <asm-generic/mman-common.h>
#include <linux/highmem.h>
#include <linux/hugetlb.h>
#include <linux/mmu_notifier.h>
#include <linux/page_idle.h>
#include <linux/pagewalk.h>
#include <linux/sched/mm.h>
#include "ops-common.h"
#ifdef CONFIG_DAMON_VADDR_KUNIT_TEST
#undef DAMON_MIN_REGION
#define DAMON_MIN_REGION 1
#endif
/*
* 't->pid' should be the pointer to the relevant 'struct pid' having reference
* count. Caller must put the returned task, unless it is NULL.
*/
static inline struct task_struct *damon_get_task_struct(struct damon_target *t)
{
return get_pid_task(t->pid, PIDTYPE_PID);
}
/*
* Get the mm_struct of the given target
*
* Caller _must_ put the mm_struct after use, unless it is NULL.
*
* Returns the mm_struct of the target on success, NULL on failure
*/
static struct mm_struct *damon_get_mm(struct damon_target *t)
{
struct task_struct *task;
struct mm_struct *mm;
task = damon_get_task_struct(t);
if (!task)
return NULL;
mm = get_task_mm(task);
put_task_struct(task);
return mm;
}
/*
* Functions for the initial monitoring target regions construction
*/
/*
* Size-evenly split a region into 'nr_pieces' small regions
*
* Returns 0 on success, or negative error code otherwise.
*/
static int damon_va_evenly_split_region(struct damon_target *t,
struct damon_region *r, unsigned int nr_pieces)
{
unsigned long sz_orig, sz_piece, orig_end;
struct damon_region *n = NULL, *next;
unsigned long start;
if (!r || !nr_pieces)
return -EINVAL;
orig_end = r->ar.end;
sz_orig = damon_sz_region(r);
sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
if (!sz_piece)
return -EINVAL;
r->ar.end = r->ar.start + sz_piece;
next = damon_next_region(r);
for (start = r->ar.end; start + sz_piece <= orig_end;
start += sz_piece) {
n = damon_new_region(start, start + sz_piece);
if (!n)
return -ENOMEM;
damon_insert_region(n, r, next, t);
r = n;
}
/* complement last region for possible rounding error */
if (n)
n->ar.end = orig_end;
return 0;
}
static unsigned long sz_range(struct damon_addr_range *r)
{
return r->end - r->start;
}
/*
* Find three regions separated by two biggest unmapped regions
*
* vma the head vma of the target address space
* regions an array of three address ranges that results will be saved
*
* This function receives an address space and finds three regions in it which
* separated by the two biggest unmapped regions in the space. Please refer to
* below comments of '__damon_va_init_regions()' function to know why this is
* necessary.
*
* Returns 0 if success, or negative error code otherwise.
*/
static int __damon_va_three_regions(struct mm_struct *mm,
struct damon_addr_range regions[3])
{
struct damon_addr_range first_gap = {0}, second_gap = {0};
VMA_ITERATOR(vmi, mm, 0);
struct vm_area_struct *vma, *prev = NULL;
unsigned long start;
/*
* Find the two biggest gaps so that first_gap > second_gap > others.
* If this is too slow, it can be optimised to examine the maple
* tree gaps.
*/
for_each_vma(vmi, vma) {
unsigned long gap;
if (!prev) {
start = vma->vm_start;
goto next;
}
gap = vma->vm_start - prev->vm_end;
if (gap > sz_range(&first_gap)) {
second_gap = first_gap;
first_gap.start = prev->vm_end;
first_gap.end = vma->vm_start;
} else if (gap > sz_range(&second_gap)) {
second_gap.start = prev->vm_end;
second_gap.end = vma->vm_start;
}
next:
prev = vma;
}
if (!sz_range(&second_gap) || !sz_range(&first_gap))
return -EINVAL;
/* Sort the two biggest gaps by address */
if (first_gap.start > second_gap.start)
swap(first_gap, second_gap);
/* Store the result */
regions[0].start = ALIGN(start, DAMON_MIN_REGION);
regions[0].end = ALIGN(first_gap.start, DAMON_MIN_REGION);
regions[1].start = ALIGN(first_gap.end, DAMON_MIN_REGION);
regions[1].end = ALIGN(second_gap.start, DAMON_MIN_REGION);
regions[2].start = ALIGN(second_gap.end, DAMON_MIN_REGION);
regions[2].end = ALIGN(prev->vm_end, DAMON_MIN_REGION);
return 0;
}
/*
* Get the three regions in the given target (task)
*
* Returns 0 on success, negative error code otherwise.
*/
static int damon_va_three_regions(struct damon_target *t,
struct damon_addr_range regions[3])
{
struct mm_struct *mm;
int rc;
mm = damon_get_mm(t);
if (!mm)
return -EINVAL;
mmap_read_lock(mm);
rc = __damon_va_three_regions(mm, regions);
mmap_read_unlock(mm);
mmput(mm);
return rc;
}
/*
* Initialize the monitoring target regions for the given target (task)
*
* t the given target
*
* Because only a number of small portions of the entire address space
* is actually mapped to the memory and accessed, monitoring the unmapped
* regions is wasteful. That said, because we can deal with small noises,
* tracking every mapping is not strictly required but could even incur a high
* overhead if the mapping frequently changes or the number of mappings is
* high. The adaptive regions adjustment mechanism will further help to deal
* with the noise by simply identifying the unmapped areas as a region that
* has no access. Moreover, applying the real mappings that would have many
* unmapped areas inside will make the adaptive mechanism quite complex. That
* said, too huge unmapped areas inside the monitoring target should be removed
* to not take the time for the adaptive mechanism.
*
* For the reason, we convert the complex mappings to three distinct regions
* that cover every mapped area of the address space. Also the two gaps
* between the three regions are the two biggest unmapped areas in the given
* address space. In detail, this function first identifies the start and the
* end of the mappings and the two biggest unmapped areas of the address space.
* Then, it constructs the three regions as below:
*
* [mappings[0]->start, big_two_unmapped_areas[0]->start)
* [big_two_unmapped_areas[0]->end, big_two_unmapped_areas[1]->start)
* [big_two_unmapped_areas[1]->end, mappings[nr_mappings - 1]->end)
*
* As usual memory map of processes is as below, the gap between the heap and
* the uppermost mmap()-ed region, and the gap between the lowermost mmap()-ed
* region and the stack will be two biggest unmapped regions. Because these
* gaps are exceptionally huge areas in usual address space, excluding these
* two biggest unmapped regions will be sufficient to make a trade-off.
*
* <heap>
* <BIG UNMAPPED REGION 1>
* <uppermost mmap()-ed region>
* (other mmap()-ed regions and small unmapped regions)
* <lowermost mmap()-ed region>
* <BIG UNMAPPED REGION 2>
* <stack>
*/
static void __damon_va_init_regions(struct damon_ctx *ctx,
struct damon_target *t)
{
struct damon_target *ti;
struct damon_region *r;
struct damon_addr_range regions[3];
unsigned long sz = 0, nr_pieces;
int i, tidx = 0;
if (damon_va_three_regions(t, regions)) {
damon_for_each_target(ti, ctx) {
if (ti == t)
break;
tidx++;
}
pr_debug("Failed to get three regions of %dth target\n", tidx);
return;
}
for (i = 0; i < 3; i++)
sz += regions[i].end - regions[i].start;
if (ctx->attrs.min_nr_regions)
sz /= ctx->attrs.min_nr_regions;
if (sz < DAMON_MIN_REGION)
sz = DAMON_MIN_REGION;
/* Set the initial three regions of the target */
for (i = 0; i < 3; i++) {
r = damon_new_region(regions[i].start, regions[i].end);
if (!r) {
pr_err("%d'th init region creation failed\n", i);
return;
}
damon_add_region(r, t);
nr_pieces = (regions[i].end - regions[i].start) / sz;
damon_va_evenly_split_region(t, r, nr_pieces);
}
}
/* Initialize '->regions_list' of every target (task) */
static void damon_va_init(struct damon_ctx *ctx)
{
struct damon_target *t;
damon_for_each_target(t, ctx) {
/* the user may set the target regions as they want */
if (!damon_nr_regions(t))
__damon_va_init_regions(ctx, t);
}
}
/*
* Update regions for current memory mappings
*/
static void damon_va_update(struct damon_ctx *ctx)
{
struct damon_addr_range three_regions[3];
struct damon_target *t;
damon_for_each_target(t, ctx) {
if (damon_va_three_regions(t, three_regions))
continue;
damon_set_regions(t, three_regions, 3);
}
}
static int damon_mkold_pmd_entry(pmd_t *pmd, unsigned long addr,
unsigned long next, struct mm_walk *walk)
{
pte_t *pte;
spinlock_t *ptl;
if (pmd_trans_huge(*pmd)) {
ptl = pmd_lock(walk->mm, pmd);
if (!pmd_present(*pmd)) {
spin_unlock(ptl);
return 0;
}
if (pmd_trans_huge(*pmd)) {
damon_pmdp_mkold(pmd, walk->vma, addr);
spin_unlock(ptl);
return 0;
}
spin_unlock(ptl);
}
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
if (!pte) {
walk->action = ACTION_AGAIN;
return 0;
}
if (!pte_present(ptep_get(pte)))
goto out;
damon_ptep_mkold(pte, walk->vma, addr);
out:
pte_unmap_unlock(pte, ptl);
return 0;
}
#ifdef CONFIG_HUGETLB_PAGE
static void damon_hugetlb_mkold(pte_t *pte, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long addr)
{
bool referenced = false;
pte_t entry = huge_ptep_get(pte);
struct folio *folio = pfn_folio(pte_pfn(entry));
folio_get(folio);
if (pte_young(entry)) {
referenced = true;
entry = pte_mkold(entry);
set_huge_pte_at(mm, addr, pte, entry);
}
#ifdef CONFIG_MMU_NOTIFIER
if (mmu_notifier_clear_young(mm, addr,
addr + huge_page_size(hstate_vma(vma))))
referenced = true;
#endif /* CONFIG_MMU_NOTIFIER */
if (referenced)
folio_set_young(folio);
folio_set_idle(folio);
folio_put(folio);
}
static int damon_mkold_hugetlb_entry(pte_t *pte, unsigned long hmask,
unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
struct hstate *h = hstate_vma(walk->vma);
spinlock_t *ptl;
pte_t entry;
ptl = huge_pte_lock(h, walk->mm, pte);
entry = huge_ptep_get(pte);
if (!pte_present(entry))
goto out;
damon_hugetlb_mkold(pte, walk->mm, walk->vma, addr);
out:
spin_unlock(ptl);
return 0;
}
#else
#define damon_mkold_hugetlb_entry NULL
#endif /* CONFIG_HUGETLB_PAGE */
static const struct mm_walk_ops damon_mkold_ops = {
.pmd_entry = damon_mkold_pmd_entry,
.hugetlb_entry = damon_mkold_hugetlb_entry,
};
static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
{
mmap_read_lock(mm);
walk_page_range(mm, addr, addr + 1, &damon_mkold_ops, NULL);
mmap_read_unlock(mm);
}
/*
* Functions for the access checking of the regions
*/
static void __damon_va_prepare_access_check(struct mm_struct *mm,
struct damon_region *r)
{
r->sampling_addr = damon_rand(r->ar.start, r->ar.end);
damon_va_mkold(mm, r->sampling_addr);
}
static void damon_va_prepare_access_checks(struct damon_ctx *ctx)
{
struct damon_target *t;
struct mm_struct *mm;
struct damon_region *r;
damon_for_each_target(t, ctx) {
mm = damon_get_mm(t);
if (!mm)
continue;
damon_for_each_region(r, t)
__damon_va_prepare_access_check(mm, r);
mmput(mm);
}
}
struct damon_young_walk_private {
/* size of the folio for the access checked virtual memory address */
unsigned long *folio_sz;
bool young;
};
static int damon_young_pmd_entry(pmd_t *pmd, unsigned long addr,
unsigned long next, struct mm_walk *walk)
{
pte_t *pte;
pte_t ptent;
spinlock_t *ptl;
struct folio *folio;
struct damon_young_walk_private *priv = walk->private;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
if (pmd_trans_huge(*pmd)) {
ptl = pmd_lock(walk->mm, pmd);
if (!pmd_present(*pmd)) {
spin_unlock(ptl);
return 0;
}
if (!pmd_trans_huge(*pmd)) {
spin_unlock(ptl);
goto regular_page;
}
folio = damon_get_folio(pmd_pfn(*pmd));
if (!folio)
goto huge_out;
if (pmd_young(*pmd) || !folio_test_idle(folio) ||
mmu_notifier_test_young(walk->mm,
addr))
priv->young = true;
*priv->folio_sz = HPAGE_PMD_SIZE;
folio_put(folio);
huge_out:
spin_unlock(ptl);
return 0;
}
regular_page:
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
if (!pte) {
walk->action = ACTION_AGAIN;
return 0;
}
ptent = ptep_get(pte);
if (!pte_present(ptent))
goto out;
folio = damon_get_folio(pte_pfn(ptent));
if (!folio)
goto out;
if (pte_young(ptent) || !folio_test_idle(folio) ||
mmu_notifier_test_young(walk->mm, addr))
priv->young = true;
*priv->folio_sz = folio_size(folio);
folio_put(folio);
out:
pte_unmap_unlock(pte, ptl);
return 0;
}
#ifdef CONFIG_HUGETLB_PAGE
static int damon_young_hugetlb_entry(pte_t *pte, unsigned long hmask,
unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
struct damon_young_walk_private *priv = walk->private;
struct hstate *h = hstate_vma(walk->vma);
struct folio *folio;
spinlock_t *ptl;
pte_t entry;
ptl = huge_pte_lock(h, walk->mm, pte);
entry = huge_ptep_get(pte);
if (!pte_present(entry))
goto out;
folio = pfn_folio(pte_pfn(entry));
folio_get(folio);
if (pte_young(entry) || !folio_test_idle(folio) ||
mmu_notifier_test_young(walk->mm, addr))
priv->young = true;
*priv->folio_sz = huge_page_size(h);
folio_put(folio);
out:
spin_unlock(ptl);
return 0;
}
#else
#define damon_young_hugetlb_entry NULL
#endif /* CONFIG_HUGETLB_PAGE */
static const struct mm_walk_ops damon_young_ops = {
.pmd_entry = damon_young_pmd_entry,
.hugetlb_entry = damon_young_hugetlb_entry,
};
static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
unsigned long *folio_sz)
{
struct damon_young_walk_private arg = {
.folio_sz = folio_sz,
.young = false,
};
mmap_read_lock(mm);
walk_page_range(mm, addr, addr + 1, &damon_young_ops, &arg);
mmap_read_unlock(mm);
return arg.young;
}
/*
* Check whether the region was accessed after the last preparation
*
* mm 'mm_struct' for the given virtual address space
* r the region to be checked
*/
static void __damon_va_check_access(struct mm_struct *mm,
struct damon_region *r, bool same_target)
{
static unsigned long last_addr;
static unsigned long last_folio_sz = PAGE_SIZE;
static bool last_accessed;
/* If the region is in the last checked page, reuse the result */
if (same_target && (ALIGN_DOWN(last_addr, last_folio_sz) ==
ALIGN_DOWN(r->sampling_addr, last_folio_sz))) {
if (last_accessed)
r->nr_accesses++;
return;
}
last_accessed = damon_va_young(mm, r->sampling_addr, &last_folio_sz);
if (last_accessed)
r->nr_accesses++;
last_addr = r->sampling_addr;
}
static unsigned int damon_va_check_accesses(struct damon_ctx *ctx)
{
struct damon_target *t;
struct mm_struct *mm;
struct damon_region *r;
unsigned int max_nr_accesses = 0;
bool same_target;
damon_for_each_target(t, ctx) {
mm = damon_get_mm(t);
if (!mm)
continue;
same_target = false;
damon_for_each_region(r, t) {
__damon_va_check_access(mm, r, same_target);
max_nr_accesses = max(r->nr_accesses, max_nr_accesses);
same_target = true;
}
mmput(mm);
}
return max_nr_accesses;
}
/*
* Functions for the target validity check and cleanup
*/
static bool damon_va_target_valid(struct damon_target *t)
{
struct task_struct *task;
task = damon_get_task_struct(t);
if (task) {
put_task_struct(task);
return true;
}
return false;
}
#ifndef CONFIG_ADVISE_SYSCALLS
static unsigned long damos_madvise(struct damon_target *target,
struct damon_region *r, int behavior)
{
return 0;
}
#else
static unsigned long damos_madvise(struct damon_target *target,
struct damon_region *r, int behavior)
{
struct mm_struct *mm;
unsigned long start = PAGE_ALIGN(r->ar.start);
unsigned long len = PAGE_ALIGN(damon_sz_region(r));
unsigned long applied;
mm = damon_get_mm(target);
if (!mm)
return 0;
applied = do_madvise(mm, start, len, behavior) ? 0 : len;
mmput(mm);
return applied;
}
#endif /* CONFIG_ADVISE_SYSCALLS */
static unsigned long damon_va_apply_scheme(struct damon_ctx *ctx,
struct damon_target *t, struct damon_region *r,
struct damos *scheme)
{
int madv_action;
switch (scheme->action) {
case DAMOS_WILLNEED:
madv_action = MADV_WILLNEED;
break;
case DAMOS_COLD:
madv_action = MADV_COLD;
break;
case DAMOS_PAGEOUT:
madv_action = MADV_PAGEOUT;
break;
case DAMOS_HUGEPAGE:
madv_action = MADV_HUGEPAGE;
break;
case DAMOS_NOHUGEPAGE:
madv_action = MADV_NOHUGEPAGE;
break;
case DAMOS_STAT:
return 0;
default:
/*
* DAMOS actions that are not yet supported by 'vaddr'.
*/
return 0;
}
return damos_madvise(t, r, madv_action);
}
static int damon_va_scheme_score(struct damon_ctx *context,
struct damon_target *t, struct damon_region *r,
struct damos *scheme)
{
switch (scheme->action) {
case DAMOS_PAGEOUT:
return damon_cold_score(context, r, scheme);
default:
break;
}
return DAMOS_MAX_SCORE;
}
static int __init damon_va_initcall(void)
{
struct damon_operations ops = {
.id = DAMON_OPS_VADDR,
.init = damon_va_init,
.update = damon_va_update,
.prepare_access_checks = damon_va_prepare_access_checks,
.check_accesses = damon_va_check_accesses,
.reset_aggregated = NULL,
.target_valid = damon_va_target_valid,
.cleanup = NULL,
.apply_scheme = damon_va_apply_scheme,
.get_scheme_score = damon_va_scheme_score,
};
/* ops for fixed virtual address ranges */
struct damon_operations ops_fvaddr = ops;
int err;
/* Don't set the monitoring target regions for the entire mapping */
ops_fvaddr.id = DAMON_OPS_FVADDR;
ops_fvaddr.init = NULL;
ops_fvaddr.update = NULL;
err = damon_register_ops(&ops);
if (err)
return err;
return damon_register_ops(&ops_fvaddr);
};
subsys_initcall(damon_va_initcall);
#include "vaddr-test.h"