linux-ext4 - Re: [PATCH RFC] block: enable RWF

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Message-ID: <35866783-2312-4e31-904d-3746510eaf56@kernel.dk>
Date: Thu, 19 Feb 2026 08:24:38 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Tal Zussman <tz2294@...umbia.edu>,
 "Tigran A. Aivazian" <aivazian.tigran@...il.com>,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Namjae Jeon <linkinjeon@...nel.org>, Sungjong Seo <sj1557.seo@...sung.com>,
 Yuezhang Mo <yuezhang.mo@...y.com>, Dave Kleikamp <shaggy@...nel.org>,
 Ryusuke Konishi <konishi.ryusuke@...il.com>,
 Viacheslav Dubeyko <slava@...eyko.com>,
 Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
 Bob Copeland <me@...copeland.com>
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
 jfs-discussion@...ts.sourceforge.net, linux-nilfs@...r.kernel.org,
 ntfs3@...ts.linux.dev, linux-karma-devel@...ts.sourceforge.net
Subject: Re: [PATCH RFC] block: enable RWF_DONTCACHE for block devices

On 2/18/26 2:13 PM, Tal Zussman wrote:
> Block device buffered reads and writes already pass through
> filemap_read() and iomap_file_buffered_write() respectively, both of
> which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
> by setting FOP_DONTCACHE in def_blk_fops.
> 
> For CONFIG_BUFFER_HEAD paths, thread the kiocb through
> block_write_begin() so that buffer_head-based I/O can use DONTCACHE
> behavior as well. Callers without a kiocb context (e.g. nilfs2 recovery)
> pass NULL, which preserves the existing behavior.
> 
> This support is useful for databases that operate on raw block devices,
> among other userspace applications.

OOO right now so I'll take a real look when I'm back, but when I
originally did this work, it's not the issue side that's the issue. It's
the pruning done from completion context, and you need to ensure that's
sane context for that (non-irq).

-- 
Jens Axboe