On Sat, Nov 04, 2017 at 04:20:07AM +0000, fdman...@kernel.org wrote:
> From: Filipe Manana <fdman...@suse.com>
>
> The patch from commit a7e3b975a0f9 ("Btrfs: fix reported number of inode
> blocks") introduced a regression where if we do a buffered write starting
> at position equal to or greater than the file's size and then stat(2) the
> file before writeback is triggered, the number of used blocks does not
> change (unless there's a prealloc/unwritten extent). Example:
>
> $ xfs_io -f -c "pwrite -S 0xab 0 64K" foobar
> $ du -h foobar
> 0 foobar
> $ sync
> $ du -h foobar
> 64K foobar
>
> The first version of that patch didn't had this regression and the second
> version, which was the one committed, was made only to address some
> performance regression detected by the intel test robots using fs_mark.
>
> This fixes the regression by setting the new delaloc bit in the range, and
> doing it at btrfs_dirty_pages() while setting the regular dealloc bit as
> well, so that this way we set both bits at once avoiding navigation of the
> inode's io tree twice. Doing it at btrfs_dirty_pages() is also the most
> meaninful place, as we should set the new dellaloc bit when if we set the
> delalloc bit, which happens only if we copied bytes into the pages at
> __btrfs_buffered_write().
>
> This was making some of LTP's du tests fail, which can be quickly run
> using a command line like the following:
>
> $ ./runltp -q -p -l /ltp.log -f commands -s du -d /mnt
>
> Fixes: a7e3b975a0f9 ("Btrfs: fix reported number of inode blocks")
> Signed-off-by: Filipe Manana <fdman...@suse.com>
FYI, I'm going to add the two patches to a 4.15 queue.
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