linux-ext4 - [Bug 218932] Serious problem with ext4 with all kernels, auto-commits do not settle to block device

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Message-ID: <bug-218932-13602-O6Zx2TSx8t@https.bugzilla.kernel.org/>
Date: Wed, 05 Jun 2024 18:32:12 +0000
From: bugzilla-daemon@...nel.org
To: linux-ext4@...r.kernel.org
Subject: [Bug 218932] Serious problem with ext4 with all kernels,
 auto-commits do not settle to block device

https://bugzilla.kernel.org/show_bug.cgi?id=218932

Theodore Tso (tytso@....edu) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |tytso@....edu
         Resolution|---                         |INVALID

--- Comment #1 from Theodore Tso (tytso@....edu) ---
This is not a bug.   What you are observing is the dirty writeback for buffered
I/O.   This is configurable; see [1], and in particular the documentation for
dirty_expire_centisecs, which you can query by looking at the contents of
/proc/sys/vm/dirty_expire_centisecs, and which you can configure by writing to
that file (e.g., "cat 500 > /proc/sys/vm/dirty_expire_centisecs").   Note that
changing dirty_expire_centisecs from 3000 (30 seconds) to 500 (5 seconds) will
have performance implications; there are Very Good Reasons why the default is
set to 30 seconds (as well it being the historic default used by Unix systems
for decades).

[1] https://docs.kernel.org/admin-guide/sysctl/vm.html

Note that if you want to make sure something is written to disk, it's best to
explicit about it, using the fsync(2) system call.

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