linux-ext4 - Re: [PATCH] ext4: Fix calculation of credits for extent tree modification

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Message-ID: <174775151764.432196.8660962659258174516.b4-ty@mit.edu>
Date: Tue, 20 May 2025 10:40:16 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Jan Kara <jack@...e.cz>
Cc: "Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Luis Chamberlain <mcgrof@...nel.org>, kdevops@...ts.linux.dev
Subject: Re: [PATCH] ext4: Fix calculation of credits for extent tree modification


On Tue, 29 Apr 2025 19:55:36 +0200, Jan Kara wrote:
> Luis and David are reporting that after running generic/750 test for 90+
> hours on 2k ext4 filesystem, they are able to trigger a warning in
> jbd2_journal_dirty_metadata() complaining that there are not enough
> credits in the running transaction started in ext4_do_writepages().
> 
> Indeed the code in ext4_do_writepages() is racy and the extent tree can
> change between the time we compute credits necessary for extent tree
> computation and the time we actually modify the extent tree. Thus it may
> happen that the number of credits actually needed is higher. Modify
> ext4_ext_index_trans_blocks() to count with the worst case of maximum
> tree depth. This can reduce the possible number of writers that can
> operate in the system in parallel (because the credit estimates now won't
> fit in one transaction) but for reasonably sized journals this shouldn't
> really be an issue. So just go with a safe and simple fix.
> 
> [...]

Applied, thanks!

[1/1] ext4: Fix calculation of credits for extent tree modification
      commit: 32a93f5bc9b9812fc710f43a4d8a6830f91e4988

Best regards,
-- 
Theodore Ts'o <tytso@....edu>