linux-kernel - Re: [PATCH v3 0/4] allow partial folio write with iomap_folio

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Message-ID: <20250825113921.2933350-1-alexjlzheng@tencent.com>
Date: Mon, 25 Aug 2025 19:39:21 +0800
From: Jinliang Zheng <alexjlzheng@...il.com>
To: hch@...radead.org
Cc: alexjlzheng@...il.com,
	alexjlzheng@...cent.com,
	brauner@...nel.org,
	djwong@...nel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-xfs@...r.kernel.org,
	yi.zhang@...wei.com
Subject: Re: [PATCH v3 0/4] allow partial folio write with iomap_folio_state

On Mon, 25 Aug 2025 02:34:30 -0700, Christoph Hellwig wrote:
> On Tue, Aug 13, 2025 at 05:15:34PM +0800, alexjlzheng@...il.com wrote:
> > From: Jinliang Zheng <alexjlzheng@...cent.com>
> > 
> > With iomap_folio_state, we can identify uptodate states at the block
> > level, and a read_folio reading can correctly handle partially
> > uptodate folios.
> > 
> > Therefore, when a partial write occurs, accept the block-aligned
> > partial write instead of rejecting the entire write.
> > 
> > For example, suppose a folio is 2MB, blocksize is 4kB, and the copied
> > bytes are 2MB-3kB.
> 
> I'd still love to see some explanation of why you are doing this.
> Do you have a workload that actually hits this regularly, and where
> it makes a difference.  Can you provide numbers to quantify them?

Thank you for your reply. :)

Actually, I discovered this while reading (and studying) the code for large
folios.

Given that short-writes are inherently unusual, I don't think this patchset
will significantly improve performance in hot paths. It might help in scenarios
with frequent memory hardware errors, but unfortunately, I haven't built a
test scenario like that.

I'm posting this patchset just because I think we can do better in exception
handling: if we can reduce unnecessary copying, why not?

Hahaha, just my personal opinion. :)

thanks,
Jinliang Zheng