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erofs: complete a missing case for inplace I/O

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Add a missing case which could cause unnecessary page allocation but
not directly use inplace I/O instead, which increases runtime extra
memory footprint.

The detail is, considering an online file-backed page, the right half
of the page is chosen to be cached (e.g. the end page of a readahead
request) and some of its data doesn't exist in managed cache, so the
pcluster will be definitely kept in the submission chain. (IOWs, it
cannot be decompressed without I/O, e.g., due to the bypass queue).

Currently, DELAYEDALLOC/TRYALLOC cases can be downgraded as NOINPLACE,
and stop online pages from inplace I/O. After this patch, unneeded page
allocations won't be observed in pickup_page_for_submission() then.

Link: https://lore.kernel.org/r/20210321183227.5182-1-hsiangkao@aol.com
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
This commit is contained in:
Gao Xiang 2021-03-22 02:32:27 +08:00
parent 30048cdac4
commit 0b964600d3
1 changed files with 29 additions and 15 deletions
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44
fs/erofs/zdata.c
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@ -104,6 +104,12 @@ enum z_erofs_collectmode {
* |_______PRIMARY_FOLLOWED_______|________PRIMARY_HOOKED___________|
*/
COLLECT_PRIMARY_HOOKED,
/*
* a weak form of COLLECT_PRIMARY_FOLLOWED, the difference is that it
* could be dispatched into bypass queue later due to uptodated managed
* pages. All related online pages cannot be reused for inplace I/O (or
* pagevec) since it can be directly decoded without I/O submission.
*/
COLLECT_PRIMARY_FOLLOWED_NOINPLACE,
/*
* The current collection has been linked with the owned chain, and
@ -186,21 +192,25 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
if (page) {
t = tag_compressed_page_justfound(page);
} else if (type == DELAYEDALLOC) {
t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
} else if (type == TRYALLOC) {
newpage = erofs_allocpage(pagepool, gfp);
if (!newpage)
goto dontalloc;
set_page_private(newpage, Z_EROFS_PREALLOCATED_PAGE);
t = tag_compressed_page_justfound(newpage);
} else { /* DONTALLOC */
dontalloc:
if (standalone)
clt->compressedpages = pages;
} else {
/* I/O is needed, no possible to decompress directly */
standalone = false;
continue;
switch (type) {
case DELAYEDALLOC:
t = tagptr_init(compressed_page_t,
PAGE_UNALLOCATED);
break;
case TRYALLOC:
newpage = erofs_allocpage(pagepool, gfp);
if (!newpage)
continue;
set_page_private(newpage,
Z_EROFS_PREALLOCATED_PAGE);
t = tag_compressed_page_justfound(newpage);
break;
default: /* DONTALLOC */
continue;
}
}
if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))
@ -214,7 +224,11 @@ dontalloc:
}
}
if (standalone) /* downgrade to PRIMARY_FOLLOWED_NOINPLACE */
/*
* don't do inplace I/O if all compressed pages are available in
* managed cache since it can be moved to the bypass queue instead.
*/
if (standalone)
clt->mode = COLLECT_PRIMARY_FOLLOWED_NOINPLACE;
}