From: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
To: Qu Wenruo <wqu@suse.com>, linux-btrfs@vger.kernel.org
Cc: Julian Taylor <julian.taylor@1und1.de>,
Filipe Manana <fdmanana@suse.com>
Subject: Re: [PATCH] btrfs: do not wait for short bulk allocation
Date: Thu, 4 Apr 2024 21:10:06 -0400 [thread overview]
Message-ID: <f80bf0eb-a775-48a7-b221-0dcee03126cf@dorminy.me> (raw)
In-Reply-To: <78e109cdbec7b11b1832822143d483509abb059e.1712266967.git.wqu@suse.com>
On 4/4/24 17:43, Qu Wenruo wrote:
> [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>
Reviewed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
> 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;
> }
prev parent reply other threads:[~2024-04-05 1:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-04 21:43 [PATCH] btrfs: do not wait for short bulk allocation Qu Wenruo
2024-04-05 1:10 ` Sweet Tea Dorminy [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f80bf0eb-a775-48a7-b221-0dcee03126cf@dorminy.me \
--to=sweettea-kernel@dorminy.me \
--cc=fdmanana@suse.com \
--cc=julian.taylor@1und1.de \
--cc=linux-btrfs@vger.kernel.org \
--cc=wqu@suse.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).