Hello, Yang.
2022년 8월 12일 (금) 오전 7:10, Andrew Morton <[email protected]>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
>
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> *** 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
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>
> ------------------------------------------------------
> From: Yang Yang <[email protected]>
> 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/[email protected]
> Signed-off-by: Yang Yang <[email protected]>
> Signed-off-by: CGEL ZTE <[email protected]>
> Cc: Balbir Singh <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
> Cc: Matthew Wilcox (Oracle) <[email protected]>
> Cc: Yang Yang <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Joonsoo Kim <[email protected]>
> Signed-off-by: Andrew Morton <[email protected]>
> ---
>
> 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.
We have discussed related question before. See:
https://lore.kernel.org/all/[email protected]/
The problem is that there is no suitable place to measure pagecache thrashing
in fs level likes swap_readpage(). We have to measure it in folio_wait_bit_common().
If we measure swap thrashing just in swap_readpage(), we will miss pagecache
thrashing. If we measure swap thrashing in swap_readpage(), and measure
pagecache thrashing in folio_wait_bit_common(), it will be rerpeated calculation.
So this patch is not perfect and it works. If one day we solve the problem of
measure thrashing in folio_wait_bit_common(), we may improve this patch correspond.
Thanks.
2022년 8월 12일 (금) 오후 12:48, CGEL <[email protected]>님이 작성:
>
> We have discussed related question before. See:
> https://lore.kernel.org/all/[email protected]/
> The problem is that there is no suitable place to measure pagecache thrashing
> in fs level likes swap_readpage(). We have to measure it in folio_wait_bit_common().
>
> If we measure swap thrashing just in swap_readpage(), we will miss pagecache
> thrashing. If we measure swap thrashing in swap_readpage(), and measure
> pagecache thrashing in folio_wait_bit_common(), it will be rerpeated calculation.
Maybe, repeated calculation issue could be easily solved by
re-entrance detection on
delayacct_thrashing_start().
Thanks.
On Fri, Aug 12, 2022 at 03:45:09PM +0900, Joonsoo Kim wrote:
> 2022년 8월 12일 (금) 오후 12:48, CGEL <[email protected]>님이 작성:
> >
> > We have discussed related question before. See:
> > https://lore.kernel.org/all/[email protected]/
> > The problem is that there is no suitable place to measure pagecache thrashing
> > in fs level likes swap_readpage(). We have to measure it in folio_wait_bit_common().
> >
> > If we measure swap thrashing just in swap_readpage(), we will miss pagecache
> > thrashing. If we measure swap thrashing in swap_readpage(), and measure
> > pagecache thrashing in folio_wait_bit_common(), it will be rerpeated calculation.
>
> Maybe, repeated calculation issue could be easily solved by
> re-entrance detection on
> delayacct_thrashing_start().
>
If no other suggestion from others, I will commit another patch
to realize this.
And I think this patch will not conflict with the later patch.
Thanks.
> Thanks.