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SubjectRe: + filemap-make-the-accounting-of-thrashing-more-consistent.patch added to mm-unstable branch
Hello, Yang.

2022년 8월 12일 (금) 오전 7:10, Andrew Morton <akpm@linux-foundation.org>님이 작성:
>
>
> The patch titled
> Subject: filemap: make the accounting of thrashing more consistent
> has been added to the -mm mm-unstable branch. Its filename is
> filemap-make-the-accounting-of-thrashing-more-consistent.patch
>
> This patch will shortly appear at
> https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/filemap-make-the-accounting-of-thrashing-more-consistent.patch
>
> This patch will later appear in the mm-unstable branch at
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
>
> Before you just go and hit "reply", please:
> a) Consider who else should be cc'ed
> b) Prefer to cc a suitable mailing list as well
> c) Ideally: find the original patch on the mailing list and do a
> reply-to-all to that, adding suitable additional cc's
>
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
>
> The -mm tree is included into linux-next via the mm-everything
> branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> and is updated there every 2-3 working days
>
> ------------------------------------------------------
> From: Yang Yang <yang.yang29@zte.com.cn>
> Subject: filemap: make the accounting of thrashing more consistent
> Date: Fri, 5 Aug 2022 03:38:39 +0000
>
> Once upon a time, we only support accounting thrashing of page cache.
> Then Joonsoo introduced workingset detection for anonymous pages and we
> gained the ability to account thrashing of them[1].
>
> So let delayacct account both the thrashing of page cache and anonymous
> pages, this could make the codes more consistent and simpler.
>
> [1] commit aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
>
> Link: https://lkml.kernel.org/r/20220805033838.1714674-1-yang.yang29@zte.com.cn
> Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
> Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Yang Yang <yang.yang29@zte.com.cn>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> Documentation/accounting/delay-accounting.rst | 2 -
> mm/filemap.c | 18 +++-------------
> 2 files changed, 5 insertions(+), 15 deletions(-)
>
> --- a/Documentation/accounting/delay-accounting.rst~filemap-make-the-accounting-of-thrashing-more-consistent
> +++ a/Documentation/accounting/delay-accounting.rst
> @@ -13,7 +13,7 @@ a) waiting for a CPU (while being runnab
> b) completion of synchronous block I/O initiated by the task
> c) swapping in pages
> d) memory reclaim
> -e) thrashing page cache
> +e) thrashing
> f) direct compact
> g) write-protect copy
>
> --- a/mm/filemap.c~filemap-make-the-accounting-of-thrashing-more-consistent
> +++ a/mm/filemap.c
> @@ -1221,15 +1221,11 @@ static inline int folio_wait_bit_common(
> struct wait_page_queue wait_page;
> wait_queue_entry_t *wait = &wait_page.wait;
> bool thrashing = false;
> - bool delayacct = false;
> unsigned long pflags;
>
> if (bit_nr == PG_locked &&
> !folio_test_uptodate(folio) && folio_test_workingset(folio)) {
> - if (!folio_test_swapbacked(folio)) {
> - delayacct_thrashing_start();
> - delayacct = true;
> - }
> + delayacct_thrashing_start();
> psi_memstall_enter(&pflags);
> thrashing = true;
> }

I think that a better place to measure swap thrashing is swap_readpage().
For some cases, like a zram, swap_readpage() is called directly rather than
loading the page onto the swap cache. Your code would miss that case.

Thanks.

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