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Date: Tue, 18 Nov 2025 13:46:23 +0100
From: Christoph Hellwig <hch@lst.de>
To: Uladzislau Rezki <urezki@gmail.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>, Alasdair Kergon <agk@redhat.com>,
	DMML <dm-devel@lists.linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Snitzer <snitzer@redhat.com>, Christoph Hellwig <hch@lst.de>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial
 write
Message-ID: <20251118124623.GA32286@lst.de>
References: <20251117105945.10179-1-urezki@gmail.com> <fff990bc-6ff9-7b34-8e80-57078de40928@redhat.com> <aRxa1wPMsJwBubjx@pc636> <73556fc8-5fbf-37cb-26b9-7cdb88f69720@redhat.com> <aRxpPFQmbB0wnmM7@milan>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Nov 18, 2025 at 01:40:28PM +0100, Uladzislau Rezki wrote:
> > If logical < physical, then the device performs read-modify-write cycle 
> > when writing blocks that are not aligned at physical block size.
> > 
> This is not true. It depends on your device and specification. If it
> can't there is the dm-ebs that does the job.

Logical blocks size is the access unit.  Physical block size is a hint
that the device might be doing RWF and thus be slow.  What driver/device
are using?  Whatever it is doing is completely broken.

(that being said aligning things to the physical block size as much
as possible is usually still a good optimization, that's why the
value exists).