From: Matthew Wilcox <willy@infradead.org>
To: Mingyu He <mingyu.he@shopee.com>
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org,
kirill@shutemov.name, bfoster@redhat.com,
Jens Axboe <axboe@kernel.dk>,
littleswimmingwhale@gmail.com
Subject: Re: [ISSUE] Read performance regression when using RWF_DONTCACHE form 8026e49 "mm/filemap: add read support for RWF_DONTCACHE"
Date: Wed, 15 Apr 2026 14:49:04 +0100 [thread overview]
Message-ID: <ad-XUOoN3wj-PnRC@casper.infradead.org> (raw)
In-Reply-To: <CAAoBcuSK38z5Nh7rGuHDFwpNvtc0W49OZKc1_d1QkCbK_nL7Ew@mail.gmail.com>
On Wed, Apr 15, 2026 at 03:28:27PM +0800, Mingyu He wrote:
> I found this feature quite useful because in many scenarios, files
> only need to be read once and then discarded. Keeping them in the page
> cache can lead to a drop in read performance during cache reclaim.
> Therefore, I conducted functional tests after the official release of
> v7.0.0. I found that in normal preadv2 read scenarios (write has not
> been tested yet), the read performance actually has a significant
> regression. I would like to discuss whether this is expected, or if my
> usage or application scenario is incorrect.
Your entire premise is wrong. This is not a magic "make I/O go faster"
flag. Comparing it to cached I/O is entirely wrong; your workload
clearly benefits from readahead and you've asked to not do readahead
by specifying RWF_DONTCACHE.
Rather you should compare against O_DIRECT reads.
prev parent reply other threads:[~2026-04-15 13:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-15 7:28 Mingyu He
2026-04-15 10:05 ` Kiryl Shutsemau
2026-04-15 11:04 ` Mingyu He
2026-04-15 13:49 ` Matthew Wilcox [this message]
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