linux-kernel - Re: [PATCH] mm/readahead: Skip fully overlapped range

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Message-ID: <93f7e2ad-563b-4db5-bab6-4ce2e994dbae@linux.intel.com>
Date: Tue, 23 Sep 2025 13:11:37 +0800
From: Aubrey Li <aubrey.li@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Matthew Wilcox <willy@...radead.org>, Nanhai Zou <nanhai.zou@...el.com>,
 Gang Deng <gang.deng@...el.com>, Tianyou Li <tianyou.li@...el.com>,
 Vinicius Gomes <vinicius.gomes@...el.com>,
 Tim Chen <tim.c.chen@...ux.intel.com>, Chen Yu <yu.c.chen@...el.com>,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
 Roman Gushchin <roman.gushchin@...ux.dev>
Subject: Re: [PATCH] mm/readahead: Skip fully overlapped range

On 9/23/25 11:49, Andrew Morton wrote:
> On Tue, 23 Sep 2025 11:59:46 +0800 Aubrey Li <aubrey.li@...ux.intel.com> wrote:
> 
>> RocksDB sequential read benchmark under high concurrency shows severe
>> lock contention. Multiple threads may issue readahead on the same file
>> simultaneously, which leads to heavy contention on the xas spinlock in
>> filemap_add_folio(). Perf profiling indicates 30%~60% of CPU time spent
>> there.
>>
>> To mitigate this issue, a readahead request will be skipped if its
>> range is fully covered by an ongoing readahead. This avoids redundant
>> work and significantly reduces lock contention. In one-second sampling,
>> contention on xas spinlock dropped from 138,314 times to 2,144 times,
>> resulting in a large performance improvement in the benchmark.
>>
>> 				w/o patch       w/ patch
>> RocksDB-readseq (ops/sec)
>> (32-threads)			1.2M		2.4M
> 
> On which kernel version?  In recent times we've made a few readahead
> changes to address issues with high concurrency and a quick retest on
> mm.git's current mm-stable branch would be interesting please.
> 

I'm on v6.16.7. Thanks Andrew for the information, let me check with mm.git.

Thanks,
-Aubrey