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From: "Huang, Ying" <ying.huang@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Zhaoyu Liu <liuzhaoyu.zackary@bytedance.com>,  ryncsn@gmail.com,
  nphamcs@gmail.com,  songmuchun@bytedance.com,  david@redhat.com,
  chrisl@kernel.org,  guo.ziliang@zte.com.cn,  yosryahmed@google.com,
  linux-kernel@vger.kernel.org,  linux-mm@kvack.org
Subject: Re: [PATCH v2] mm: swap: prejudgement swap_has_cache to avoid page
 allocation
In-Reply-To: <20240408132704.f966adc8d3928df4d3b8c0a9@linux-foundation.org>
	(Andrew Morton's message of "Mon, 8 Apr 2024 13:27:04 -0700")
References: <20240408121439.GA252652@bytedance>
	<20240408132704.f966adc8d3928df4d3b8c0a9@linux-foundation.org>
Date: Tue, 09 Apr 2024 09:07:29 +0800
Message-ID: <87edbf8hta.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Andrew Morton <akpm@linux-foundation.org> writes:

> On Mon, 8 Apr 2024 20:14:39 +0800 Zhaoyu Liu <liuzhaoyu.zackary@bytedance.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