linux-kernel - Re: [PATCH] xfs: fix the judgment of whether the file already has extents

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Message-ID: <Zx9cLakpnJBAV1am@infradead.org>
Date: Mon, 28 Oct 2024 02:41:01 -0700
From: Christoph Hellwig <hch@...radead.org>
To: alexjlzheng@...il.com
Cc: cem@...nel.org, djwong@...nel.org, chandanbabu@...nel.org,
	dchinner@...hat.com, zhangjiachen.jaycee@...edance.com,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jinliang Zheng <alexjlzheng@...cent.com>
Subject: Re: [PATCH] xfs: fix the judgment of whether the file already has
 extents

On Sun, Oct 27, 2024 at 02:01:16AM +0800, alexjlzheng@...il.com wrote:
> From: Jinliang Zheng <alexjlzheng@...cent.com>
> 
> When we call create(), lseek() and write() sequentially, offset != 0
> cannot be used as a judgment condition for whether the file already
> has extents.
> 
> This patch uses prev.br_startoff instead of offset != 0.

This changed the predicate from "are we at offset 0" to "are there
any allocations before that".  That's a pretty big semantic change.
Maybe a good one, maybe not.  Can you explain what workload it helps
you with?