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

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Message-ID: <20251119054524.GA19993@lst.de>
Date: Wed, 19 Nov 2025 06:45:24 +0100
From: Christoph Hellwig <hch@....de>
To: Mikulas Patocka <mpatocka@...hat.com>
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>, Christoph Hellwig <hch@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dm-bufio: align write boundary on
 bdev_logical_block_size

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.