linux-kernel - Re: [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks

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Date: Fri, 26 Apr 2024 23:59:03 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	"Darrick J. Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	brauner@...nel.org, david@...morbit.com, chandanbabu@...nel.org,
	tytso@....edu, jack@...e.cz, yi.zhang@...wei.com,
	chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v5 4/9] xfs: convert delayed extents to unwritten when
 zeroing post eof blocks

On Fri, Apr 26, 2024 at 03:18:17PM +0800, Zhang Yi wrote:
> I've had the same idea before, I asked Dave and he explained that Linux
> could leak data beyond EOF page for some cases, e.g. mmap() can write to
> the EOF page beyond EOF without failing, and the data in that EOF page
> could be non-zeroed by mmap(), so the zeroing is still needed now.
> 
> OTOH, if we free the delalloc and unwritten blocks beyond EOF blocks, he
> said it could lead to some performance problems and make thinks
> complicated to deal with the trimming of EOF block. Please see [1]
> for details and maybe Dave could explain more.

Oh well.  Given that we're full in on the speculative allocations
we might as well deal with it.