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

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Date: Mon, 8 Apr 2024 13:27:04 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Zhaoyu Liu <liuzhaoyu.zackary@...edance.com>
Cc: ryncsn@...il.com, nphamcs@...il.com, ying.huang@...el.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

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?

> 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.