On Fri, Mar 25, 2016 at 01:26:00PM -0400, Josef Bacik wrote: > Before we write into prealloc/nocow space we have to make sure that there are > no > references to the extents we are writing into, which means checking the extent > tree and csum tree in the case of nocow. So we don't want to do the nocow > dance > unless we can't reserve data space, since it's a serious drag on performance. > With the following sequence > > fallocate -l10737418240 /mnt/btrfs-test/file > cp --reflink /mnt/btrfs-test/file /mnt/btrfs-test/link > fio --name=randwrite --rw=randwrite --bs=4k --filename=/mnt/btrfs-test/file \ > --end_fsync=1 > > we get the worst case scenario where we have to fall back on to doing the > check > anyway. > > Without this patch > lat (usec): min=5, max=111598, avg=27.65, stdev=124.51 > write: io=10240MB, bw=126876KB/s, iops=31718, runt= 82646msec > > With this patch > lat (usec): min=3, max=91210, avg=14.09, stdev=110.62 > write: io=10240MB, bw=212753KB/s, iops=53188, runt= 49286msec > > We get twice the throughput, half of the runtime, and half of the average > latency. Thanks,
I've submitted a similar one, but looks like this one is cleaner, I forgot to remove the goto reserve_metadata. Thanks, -liubo > > Signed-off-by: Josef Bacik <[email protected]> > --- > fs/btrfs/file.c | 44 ++++++++++++++++++++++---------------------- > 1 file changed, 22 insertions(+), 22 deletions(-) > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index 0ce4bb3..7c80208 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -1534,30 +1534,30 @@ static noinline ssize_t __btrfs_buffered_write(struct > file *file, > reserve_bytes = round_up(write_bytes + sector_offset, > root->sectorsize); > > - if ((BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | > - BTRFS_INODE_PREALLOC)) && > - check_can_nocow(inode, pos, &write_bytes) > 0) { > - /* > - * For nodata cow case, no need to reserve > - * data space. > - */ > - only_release_metadata = true; > - /* > - * our prealloc extent may be smaller than > - * write_bytes, so scale down. > - */ > - num_pages = DIV_ROUND_UP(write_bytes + offset, > - PAGE_CACHE_SIZE); > - reserve_bytes = round_up(write_bytes + sector_offset, > - root->sectorsize); > - goto reserve_metadata; > - } > - > ret = btrfs_check_data_free_space(inode, pos, write_bytes); > - if (ret < 0) > - break; > + if (ret < 0) { > + if ((BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | > + BTRFS_INODE_PREALLOC)) && > + check_can_nocow(inode, pos, &write_bytes) > 0) { > + /* > + * For nodata cow case, no need to reserve > + * data space. > + */ > + only_release_metadata = true; > + /* > + * our prealloc extent may be smaller than > + * write_bytes, so scale down. > + */ > + num_pages = DIV_ROUND_UP(write_bytes + offset, > + PAGE_CACHE_SIZE); > + reserve_bytes = round_up(write_bytes + > + sector_offset, > + root->sectorsize); > + } else { > + break; > + } > + } > > -reserve_metadata: > ret = btrfs_delalloc_reserve_metadata(inode, reserve_bytes); > if (ret) { > if (!only_release_metadata) > -- > 2.5.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
