linux-kernel - Re: [PATCH RFC 4/7] md/raid10: convert read/write to use bio_submit

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Message-ID: <aK60bmotWLT50qt5@infradead.org>
Date: Wed, 27 Aug 2025 00:31:58 -0700
From: Christoph Hellwig <hch@...radead.org>
To: anthony <antmbox@...ngman.org.uk>
Cc: Yu Kuai <yukuai1@...weicloud.com>,
	Christoph Hellwig <hch@...radead.org>, colyli@...nel.org,
	hare@...e.de, tieren@...as.com, axboe@...nel.dk, tj@...nel.org,
	josef@...icpanda.com, song@...nel.org, akpm@...ux-foundation.org,
	neil@...wn.name, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-raid@...r.kernel.org, yi.zhang@...wei.com,
	yangerkun@...wei.com, johnny.chenyi@...wei.com,
	John Garry <john.g.garry@...cle.com>,
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC 4/7] md/raid10: convert read/write to use
 bio_submit_split()

On Tue, Aug 26, 2025 at 06:35:10PM +0100, anthony wrote:
> On 26/08/2025 10:14, Yu Kuai wrote:
> > > Umm, that's actually a red flag.  If a device guarantees atomic behavior
> > > it can't just fail it.  So I think REQ_ATOMIC should be disallowed
> > > for md raid with bad block tracking.
> > > 
> > 
> > I agree that do not look good, however, John explained while adding this
> > that user should retry and fallback without REQ_ATOMIC to make things
> > work as usual.
> 
> Whether a device promises atomic write is orthogonal to whether that write
> succeeds - it could fail for a whole host of reasons, so why can't "this is
> too big to be atomic" just be another reason for failing?

Too big to be atomic is a valid failure reason.  But the limit needs
to be documented in the queue limits beforehand.