From: Christoph Hellwig <hch@infradead.org>
To: David Hildenbrand <david@redhat.com>
Cc: Jan Kara <jack@suse.cz>, Matthew Wilcox <willy@infradead.org>,
Christoph Hellwig <hch@infradead.org>, Qu Wenruo <wqu@suse.com>,
linux-btrfs@vger.kernel.org, djwong@kernel.org,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org, linux-mm@kvack.org,
martin.petersen@oracle.com, jack@suse.com
Subject: Re: O_DIRECT vs BLK_FEAT_STABLE_WRITES, was Re: [PATCH] btrfs: never trust the bio from direct IO
Date: Tue, 21 Oct 2025 00:49:49 -0700 [thread overview]
Message-ID: <aPc7HVRJYXA1hT8h@infradead.org> (raw)
In-Reply-To: <5bd1d360-bee0-4fa2-80c8-476519e98b00@redhat.com>
On Mon, Oct 20, 2025 at 09:00:50PM +0200, David Hildenbrand wrote:
> Just FYI, because it might be interesting in this context.
>
> For anonymous memory we have this working by only writing the folio out if
> it is completely unmapped and there are no unexpected folio references/pins
> (see pageout()), and only allowing to write to such a folio ("reuse") if
> SWP_STABLE_WRITES is not set (see do_swap_page()).
>
> So once we start writeback the folio has no writable page table mappings
> (unmapped) and no GUP pins. Consequently, when trying to write to it we can
> just fallback to creating a page copy without causing trouble with GUP pins.
Yeah. But anonymous is the easy case, the pain is direct I/O to file
mappings. Mapping the right answer is to just fail pinning them and fall
back to (dontcache) buffered I/O.
next prev parent reply other threads:[~2025-10-21 7:49 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-20 9:19 [PATCH] btrfs: never trust the bio from direct IO Qu Wenruo
2025-10-20 10:00 ` O_DIRECT vs BLK_FEAT_STABLE_WRITES, was " Christoph Hellwig
2025-10-20 10:24 ` Qu Wenruo
2025-10-20 11:45 ` Christoph Hellwig
2025-10-20 11:16 ` Jan Kara
2025-10-20 11:44 ` Christoph Hellwig
2025-10-20 13:59 ` Jan Kara
2025-10-20 14:59 ` Matthew Wilcox
2025-10-20 15:58 ` Jan Kara
2025-10-20 17:55 ` John Hubbard
2025-10-21 8:27 ` Jan Kara
2025-10-21 16:56 ` John Hubbard
2025-10-20 19:00 ` David Hildenbrand
2025-10-21 7:49 ` Christoph Hellwig [this message]
2025-10-21 7:57 ` David Hildenbrand
2025-10-21 9:33 ` Jan Kara
2025-10-21 9:43 ` David Hildenbrand
2025-10-21 9:22 ` Jan Kara
2025-10-21 9:37 ` David Hildenbrand
2025-10-21 9:52 ` Jan Kara
2025-10-21 3:17 ` Qu Wenruo
2025-10-21 7:48 ` Christoph Hellwig
2025-10-21 8:15 ` Qu Wenruo
2025-10-21 11:30 ` Johannes Thumshirn
2025-10-22 2:27 ` Qu Wenruo
2025-10-22 5:04 ` hch
2025-10-22 6:17 ` Qu Wenruo
2025-10-22 6:24 ` hch
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