[Bug 16380] ext2/ext4 filesystem "hangs" for a few seconds when trying to write a lot of data to a freshly RW mounted FS

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https://bugzilla.kernel.org/show_bug.cgi?id=16380





--- Comment #14 from Artem S. Tashkinov <t.artem@mailcity.com>  2012-08-04 18:51:24 ---
(In reply to comment #12)
> I wasn't able to duplicate this with an underlying ext4 file system, with the
> loop file system being ext2, using a 3.5 kernel on a system with 16G.
> 
> I tried both using a variety of small and medium sized files, as well as one
> very large file, and I didn't see any unexplained stuttering in write
> bandwidth.   (There were times when cp -r was clearly writing to the in-memory
> page cache, and the writeback hadn't begone yet.   There were also times when
> we couldn't do any more writing, because we were busy reading from the source
> drive.  But it all looked pretty normal to me.)

Hm, I cannot reproduce the problem with a loop device on top of tmpfs either,
but I've just checked my 250GB ext4 partition and the bug is still there:

When I try to copy a 3GB file (residing in tmpfs so it's all cached) to it,
there's a 4 (four) seconds delay before a single byte gets written to the
destination partition. After that all consequent files get written without any
delays.

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