| Message ID | 1458926760-17563-15-git-send-email-jbacik@fb.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
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 <jbacik@fb.com> > --- > 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 majordomo@vger.kernel.org > 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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)
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, Signed-off-by: Josef Bacik <jbacik@fb.com> --- fs/btrfs/file.c | 44 ++++++++++++++++++++++---------------------- 1 file changed, 22 insertions(+), 22 deletions(-)