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

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Message-ID: <aRxpq2RH3v4Dz33q@milan>
Date: Tue, 18 Nov 2025 13:42:19 +0100
From: Uladzislau Rezki <urezki@...il.com>
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 12:15:43PM +0100, Mikulas Patocka wrote:
> 
> 
> On Mon, 17 Nov 2025, Benjamin Marzinski wrote:
> 
> > On Mon, Oct 20, 2025 at 02:48:13PM +0200, Mikulas Patocka wrote:
> > > 
> > > 
> > > On Mon, 20 Oct 2025, Uladzislau Rezki (Sony) wrote:
> > > 
> > > > When performing a read-modify-write(RMW) operation, any modification
> > > > to a buffered block must cause the entire buffer to be marked dirty.
> > > > 
> > > > Marking only a subrange as dirty is incorrect because the underlying
> > > > device block size(ubs) defines the minimum read/write granularity. A
> > > > lower device can perform I/O only on regions which are fully aligned
> > > > and sized to ubs.
> > > 
> > > Hi
> > > 
> > > I think it would be better to fix this in dm-bufio, so that other dm-bufio 
> > > users would also benefit from the fix.
> > 
> > This looks to me like it should accomplish the same thing as
> > Uladzislau's patch. But I think there could still be problems with other
> > dm-bufio users, for devices where the blocksize is larger than 4k.
> 
> Yes, but Uladzislau said that this patch doesn't work for him. So, I 
> suspect that he has "logical_block_size" set incorrectly.
> 
Indeed. Because logical is < physical in my case. Your change does not fix
it because of I/O size is equal to physical.

--
Uladzislau Rezki