linux-kernel - Re: + filemap-make-the-accounting-of-thrashing-more-consistent.patch added to mm-unstable branch

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Date:   Fri, 12 Aug 2022 03:48:48 +0000
From:   CGEL <cgel.zte@...il.com>
To:     Joonsoo Kim <js1304@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, mm-commits@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Hildenbrand <david@...hat.com>, corbet@....net,
        bsingharora@...il.com, yang.yang29@....com.cn,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: + filemap-make-the-accounting-of-thrashing-more-consistent.patch
 added to mm-unstable branch

We have discussed related question before. See:
https://lore.kernel.org/all/Yio17pXawRuuVJFO@cmpxchg.org/
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.