linux-kernel - Re: [PATCH v2] mm: swap: prejudgement swap_has

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Date: Tue, 09 Apr 2024 09:07:29 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Zhaoyu Liu <liuzhaoyu.zackary@...edance.com>,  ryncsn@...il.com,
  nphamcs@...il.com,  songmuchun@...edance.com,  david@...hat.com,
  chrisl@...nel.org,  guo.ziliang@....com.cn,  yosryahmed@...gle.com,
  linux-kernel@...r.kernel.org,  linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: swap: prejudgement swap_has_cache to avoid page
 allocation

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Mon, 8 Apr 2024 20:14:39 +0800 Zhaoyu Liu <liuzhaoyu.zackary@...edance.com> wrote:
>
>> Based on qemu arm64 - latest kernel + 100M memory + 1024M swapfile.
>> Create 1G anon mmap and set it to shared, and has two processes
>> randomly access the shared memory. When they are racing on swap cache,
>> on average, each "alloc_pages_mpol + swapcache_prepare + folio_put"
>> took about 1475 us.
>
> And what effect does this patch have upon the measured time?  ANd upon
> overall runtime?

And the patch will cause increased lock contention, please test with
more processes and perhaps HDD swap device too.

>> So skip page allocation if SWAP_HAS_CACHE was set, just
>> schedule_timeout_uninterruptible and continue to acquire page
>> via filemap_get_folio() from swap cache, to speedup
>> __read_swap_cache_async.

--
Best Regards,
Huang, Ying