linux-kernel - Re: [PATCH] dm-bufio: align write boundary on bdev_logical_block

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Message-ID: <f8394fce-dc49-661a-6960-a816094d6da4@redhat.com>
Date: Wed, 19 Nov 2025 18:13:56 +0100 (CET)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Christoph Hellwig <hch@....de>
cc: Benjamin Marzinski <bmarzins@...hat.com>, 
    "Uladzislau Rezki (Sony)" <urezki@...il.com>, 
    Alasdair Kergon <agk@...hat.com>, DMML <dm-devel@...ts.linux.dev>, 
    Andrew Morton <akpm@...ux-foundation.org>, 
    Mike Snitzer <snitzer@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dm-bufio: align write boundary on
 bdev_logical_block_size



On Wed, 19 Nov 2025, Christoph Hellwig wrote:

> On Tue, Nov 18, 2025 at 06:45:55PM +0100, Mikulas Patocka wrote:
> > I changed the patch below, so that it aligns write bios on 
> > max3(DM_BUFIO_WRITE_ALIGN, bdev_logical_block_size(b->c->bdev), 
> > bdev_physical_block_size(b->c->bdev)); - so that if physical block size is 
> > greater than logical block size, the writes are aligned so that the device 
> > doesn't do read-modify-write.
> 
> That doesn't make any sense whatsoever.  The physical block size must
> be >= logical block size, and the block enforces that.

OK, so I changed it to max(DM_BUFIO_WRITE_ALIGN, 
bdev_physical_block_size(b->c->bdev))

Mikulas