linux-kernel - Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial write

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Message-ID: <aSSeYQOl1db19yoJ@pc636>
Date: Mon, 24 Nov 2025 19:05:21 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Christoph Hellwig <hch@....de>
Cc: Uladzislau Rezki <urezki@...il.com>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Benjamin Marzinski <bmarzins@...hat.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: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial
 write

On Mon, Nov 24, 2025 at 06:00:37PM +0100, Christoph Hellwig wrote:
> On Mon, Nov 24, 2025 at 04:30:25PM +0100, Uladzislau Rezki wrote:
> > > 
> > > > 
> > > > Why in dm-ebs we need to offload partial buffer < ubf size?
> > > 
> > > I don't understand this question.  What is ubf?  What does partial
> > > buffer mean in this context, and what does offload mean?
> > > 
> > That was a typo :) i meant ubs - which is underlying block size or number
> > of sectors which define the logical block size of the device. In our case
> > it is 8K thus is 16 = 512 * 16 = 8K.
> > 
> > Partial buffer means, in context of dm-ebs, that within 8K buffer only
> > part of it can be modified. For example, since we emulate 512B to 8K
> > from upper layer to the device, a file system can write for example
> > just first 4K within 8K window buffer and only that part is marked as
> > dirty.
> > 
> > offloading or imposing the data to the lower layer. i.e. writing dirty
> > buffers to the device calling submit_io().
> > 
> > Is it better? It might be that i missed something, feel free to correct.
> 
> I'm still lost what the question is, sorry.
> 
No problem, i am fine with it.

Thank you for your input especially explaining the difference
between logical_block_size and physical_block_size for nvme device.

Appreciate it!

--
Uladzislau Rezki