From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Cc: Julian Taylor <julian.taylor@1und1.de>,
Filipe Manana <fdmanana@suse.com>
Subject: [PATCH] btrfs: do not wait for short bulk allocation
Date: Fri, 5 Apr 2024 08:13:11 +1030 [thread overview]
Message-ID: <78e109cdbec7b11b1832822143d483509abb059e.1712266967.git.wqu@suse.com> (raw)
[BUG]
There is a recent report that when memory pressure is high (including
cached pages), btrfs can spend most of its time on memory allocation in
btrfs_alloc_page_array() for compressed read/write.
[CAUSE]
For btrfs_alloc_page_array() we always go alloc_pages_bulk_array(), and
even if the bulk allocation failed (fell back to single page
allocation) we still retry but with extra memalloc_retry_wait().
If the bulk alloc only returned one page a time, we would spend a lot of
time on the retry wait.
The behavior was introduced in commit 395cb57e8560 ("btrfs: wait between
incomplete batch memory allocations").
[FIX]
Although the commit mentioned that other filesystems do the wait, it's
not the case at least nowadays.
All the mainlined filesystems only call memalloc_retry_wait() if they
failed to allocate any page (not only for bulk allocation).
If there is any progress, they won't call memalloc_retry_wait() at all.
For example, xfs_buf_alloc_pages() would only call memalloc_retry_wait()
if there is no allocation progress at all, and the call is not for
metadata readahead.
So I don't believe we should call memalloc_retry_wait() unconditionally
for short allocation.
This patch would only call memalloc_retry_wait() if failed to allocate
any page for tree block allocation (which goes with __GFP_NOFAIL and may
not need the special handling anyway), and reduce the latency for
btrfs_alloc_page_array().
Reported-by: Julian Taylor <julian.taylor@1und1.de>
Tested-by: Julian Taylor <julian.taylor@1und1.de>
Link: https://lore.kernel.org/all/8966c095-cbe7-4d22-9784-a647d1bf27c3@1und1.de/
Fixes: 395cb57e8560 ("btrfs: wait between incomplete batch memory allocations")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Changelog:
v3:
- Remove wait part completely
For NOFAIL metadata allocation, the allocation itself should not fail.
For regular allocation, we can afford the failure anyway.
v2:
- Still use bulk allocation function
Since alloc_pages_bulk_array() would fall back to single page
allocation by itself, there is no need to go alloc_page() manually.
- Update the commit message to indicate other fses do not call
memalloc_retry_wait() unconditionally
In fact, they only call it when they need to retry hard and can not
really fail.
---
fs/btrfs/extent_io.c | 18 ++++--------------
1 file changed, 4 insertions(+), 14 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index bbdcb7475cea..48476f8fcf79 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -712,31 +712,21 @@ int btrfs_alloc_folio_array(unsigned int nr_folios, struct folio **folio_array,
int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array,
gfp_t extra_gfp)
{
+ const gfp_t gfp = GFP_NOFS | extra_gfp;
unsigned int allocated;
for (allocated = 0; allocated < nr_pages;) {
unsigned int last = allocated;
- allocated = alloc_pages_bulk_array(GFP_NOFS | extra_gfp,
- nr_pages, page_array);
-
- if (allocated == nr_pages)
- return 0;
-
- /*
- * During this iteration, no page could be allocated, even
- * though alloc_pages_bulk_array() falls back to alloc_page()
- * if it could not bulk-allocate. So we must be out of memory.
- */
- if (allocated == last) {
+ allocated = alloc_pages_bulk_array(gfp, nr_pages, page_array);
+ if (unlikely(allocated == last)) {
+ /* Fail and do cleanup. */
for (int i = 0; i < allocated; i++) {
__free_page(page_array[i]);
page_array[i] = NULL;
}
return -ENOMEM;
}
-
- memalloc_retry_wait(GFP_NOFS);
}
return 0;
}
--
2.44.0
next reply other threads:[~2024-04-04 21:43 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-04 21:43 Qu Wenruo [this message]
2024-04-05 1:10 ` [PATCH] btrfs: do not wait for short bulk allocation Sweet Tea Dorminy
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