linux-ext4 - Re: [PATCH 2/2] ext4: Remove array of buffer_heads from mext_page

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Message-ID: <20240627202022.GC419129@mit.edu>
Date: Thu, 27 Jun 2024 16:20:22 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH 2/2] ext4: Remove array of buffer_heads from
 mext_page_mkuptodate()

On Thu, May 16, 2024 at 07:16:51PM +0100, Matthew Wilcox (Oracle) wrote:
> The current code iterates over the list of buffer_heads, finds the
> !uptodate ones and reads them, waiting for each one before submitting
> the next one.  Instead, submit all the read requests before waiting
> for each of the needed ones.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

Hey Willy,

This patch is causing ext4/020 (which tests the EXT4_IOC_MOVE_EXT
ioctl used by e4defrag).  This can be easily reproduced via:
"kvm-xfstests -c ext4/4k ext4/020".  From
/results/ext4/results-4k/ext4/020.out.bad:

   QA output created by 020
   wrote 1048576/1048576 bytes at offset 0
   XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
   wrote 1023/1023 bytes at offset 0
   XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
   md5sum: WARNING: 1 computed checksum did NOT match
   SCRATCH_MNT/020.orig: FAILED

I'm going to drop both this patch and the preceeding patch in this
series ("ext4: reduce stack usage in ext4_mpage_readpages()") pending
further investigation.

							- Ted