On Thu 03-05-12 11:43:11, Wu Fengguang wrote: > This helps write performance when setting the dirty threshold to tiny numbers. > > 3.4.0-rc2 3.4.0-rc2-btrfs4+ > ------------ ------------------------ > 96.92 -0.4% 96.54 bay/thresh=1000M/btrfs-100dd-1-3.4.0-rc2 > 98.47 +0.0% 98.50 bay/thresh=1000M/btrfs-10dd-1-3.4.0-rc2 > 99.38 -0.3% 99.06 bay/thresh=1000M/btrfs-1dd-1-3.4.0-rc2 > 98.04 -0.0% 98.02 bay/thresh=100M/btrfs-100dd-1-3.4.0-rc2 > 98.68 +0.3% 98.98 bay/thresh=100M/btrfs-10dd-1-3.4.0-rc2 > 99.34 -0.0% 99.31 bay/thresh=100M/btrfs-1dd-1-3.4.0-rc2 > ==> 88.98 +9.6% 97.53 bay/thresh=10M/btrfs-10dd-1-3.4.0-rc2 > ==> 86.99 +13.1% 98.39 bay/thresh=10M/btrfs-1dd-1-3.4.0-rc2 > ==> 2.75 +2442.4% 69.88 bay/thresh=1M/btrfs-10dd-1-3.4.0-rc2 > ==> 3.31 +2634.1% 90.54 bay/thresh=1M/btrfs-1dd-1-3.4.0-rc2 > > Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx> > --- > fs/btrfs/disk-io.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > --- linux-next.orig/fs/btrfs/disk-io.c 2012-05-02 14:04:00.989262395 +0800 > +++ linux-next/fs/btrfs/disk-io.c 2012-05-02 14:04:01.773262414 +0800 > @@ -930,7 +930,8 @@ static int btree_writepages(struct addre > > /* this is a bit racy, but that's ok */ > num_dirty = root->fs_info->dirty_metadata_bytes; > - if (num_dirty < thresh) > + if (num_dirty < min(thresh, > + global_dirty_limit << (PAGE_CACHE_SHIFT-2))) > return 0; > } > return btree_write_cache_pages(mapping, wbc); Frankly, that whole condition on WB_SYNC_NONE in btree_writepages() looks like a hack. I think we also had problems with this condition when we tried to change b_more_io list handling. I found rather terse commit message explaining the code: Btrfs: Limit btree writeback to prevent seeks Which I kind of understand but is it that bad? Also I think last time we stumbled over this code we were discussing that these dirty metadata would be simply hidden from mm which would solve the problem of flusher thread trying to outsmart the filesystem... But I guess noone had time to implement this for btrfs. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
