From: Christoph Hellwig <hch@lst.de>
To: Mike Snitzer <snitzer@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
Chuck Lever <cel@kernel.org>, Jeff Layton <jlayton@kernel.org>,
linux-nfs@vger.kernel.org, NeilBrown <neil@brown.name>,
Olga Kornievskaia <okorniev@redhat.com>,
Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH v10 0/7] mm, iomap, NFSD: stop uncached writes reading back shared pages
Date: Wed, 4 Nov 2026 10:17:40 +0100 [thread overview]
Message-ID: <20261104091740.GB31130@lst.de> (raw)
In-Reply-To: <20261103211754.35352-1-snitzer@kernel.org>
On Tue, Nov 03, 2026 at 04:17:47PM -0500, Mike Snitzer wrote:
> Hi,
>
> An uncached (RWF_DONTCACHE) buffered write drops each folio it writes
> once the folio is written back. A folio that the write covers only
> partly is shared with the neighbouring write. If it is dropped before
> the neighbour writes its part, the neighbour reads it back from disk
> first. 32 threads writing interleaved records to one XFS file, 4 KiB
> pages, before and after 5/7:
Very colourful terminology here. Who is "the neighbour". How do we
know a "neighbour" exists and what it wants to do?
In general if the user gave a very clear indication that the data
should not be cached, it is a bit awkward to second uess that.
Especially if the expectations are not very clearly documented.
prev parent reply other threads:[~2026-11-04 9:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-03 21:17 [PATCH v10 0/7] mm, iomap, NFSD: stop uncached writes reading back shared pages Mike Snitzer
2026-11-03 21:17 ` [PATCH v10 1/7] mm: move clearing the uncached flag of a found folio into a helper Mike Snitzer
2026-11-04 9:17 ` Christoph Hellwig
2026-11-03 21:17 ` [PATCH v10 2/7] mm: take a folio off WB_DONTCACHE_DIRTY only if it was counted there Mike Snitzer
2026-11-03 21:17 ` [PATCH v10 3/7] mm: expose WB_DONTCACHE_DIRTY in bdi debugfs stats Mike Snitzer
2026-11-03 21:17 ` [PATCH v10 4/7] mm: add folio_mark_dropbehind() to mark a folio dropbehind and account it Mike Snitzer
2026-11-04 21:18 ` sashiko-bot
2026-11-03 21:17 ` [PATCH v10 5/7] mm, iomap: keep a partly covered page until an uncached write completes it Mike Snitzer
2026-11-03 21:17 ` [PATCH v10 6/7] mm, iomap: let an uncached writer complete its shared pages itself Mike Snitzer
2026-11-04 21:18 ` sashiko-bot
2026-11-03 21:17 ` [PATCH v10 7/7] NFSD: drop a shared boundary page only once both WRITEs have written it Mike Snitzer
2026-11-04 9:15 ` Christoph Hellwig
2026-11-04 17:01 ` Mike Snitzer
2026-11-04 9:17 ` Christoph Hellwig [this message]
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