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Date: Mon, 26 Jan 2026 13:47:38 +0100
From: Christoph Hellwig <hch@lst.de>
To: Anuj gupta <anuj1072538@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Christian Brauner <brauner@kernel.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Carlos Maiolino <cem@kernel.org>, Qu Wenruo <wqu@suse.com>,
	Al Viro <viro@zeniv.linux.org.uk>, linux-block@vger.kernel.org,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: bounce buffer direct I/O when stable pages are required v3
Message-ID: <20260126124738.GA28035@lst.de>
References: <20260126055406.1421026-1-hch@lst.de> <CACzX3At3fS19fmp8wOq29rHK-yw0KFp1bAvTdo9NC9eQj4E=pw@mail.gmail.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Jan 26, 2026 at 04:24:03PM +0530, Anuj gupta wrote:
> As Keith suggested, here are the QD1 latency numbers (in usec)

Thanks a gain for the benchmarks!

I'd be curious what improvement you see with the iomap-pi series on
Optane, as that drops one of the context switches on read again,
and the less efficiently managed one at that:

git://git.infradead.org/users/hch/misc.git iomap-pi
https://git.infradead.org/?p=users/hch/misc.git;a=shortlog;h=refs/heads/iomap-pi

Otherwise the only thing we can do to get data integrity and performance
is better interfaces.  I think for reads we could do that relatively
easily with a version of Joanne's kernel-managed buffer rings that can
only be mapped into userspace read-only.  Writes will be more difficult
for anything that isn't a trust-worthy kernel provided buffer
unfortunately, but then again the write degradation is less.