On Thu, 17 Mar 2016 15:16:15 -0700 Liu Bo <bo.li....@oracle.com> wrote:
> For nocow/prealloc files, we try our best to not allocate space, however, > this ends up a huge performance regression since it's expensive to check > if data is shared. > > Let's go back to only go check shared data once we're not able to allocate > space. As mentioned by Holger there's another patch modifying the same function: https://git.kernel.org/cgit/linux/kernel/git/mason/linux-btrfs.git/commit/fs/btrfs?h=integration-4.6&id=4da2e26a2a32b174878744bd0f07db180c875f26 and that one fixes a serious regression in the 4.4 series. I did not try yours, but could you please ensure that you do not hit the described problem with your version of the patch, or perhaps even better, consider re-testing performance and then basing any further performance optimizations upon a state with no known grave functionality bugs (i.e. with the above patch applied). Thanks > The test was made against a tmpfs backed loop device: > > xfs_io -f -c "falloc 0 400M" foobar > xfs_io -c "pwrite -W -b 4096 0 400M" foobar > > Vanilla: > wrote 419430400/419430400 bytes at offset 0 > 400 MiB, 102400 ops; 0:00:01.00 (200.015 MiB/sec and 51203.8403 ops/sec) > > Patched kernel: > wrote 419430400/419430400 bytes at offset 0 > 400 MiB, 102400 ops; 0:00:01.00 (346.137 MiB/sec and 88610.9796 ops/sec) > > Signed-off-by: Liu Bo <bo.li....@oracle.com> > --- > fs/btrfs/file.c | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c > index 098bb8f..f66c1bc 100644 > --- a/fs/btrfs/file.c > +++ b/fs/btrfs/file.c > @@ -1525,16 +1525,12 @@ static noinline ssize_t __btrfs_buffered_write(struct > file *file, > > reserve_bytes = num_pages << PAGE_CACHE_SHIFT; > > - if (BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | > - BTRFS_INODE_PREALLOC)) { > + ret = btrfs_check_data_free_space(inode, pos, write_bytes); > + if (ret == -ENOSPC && > + BTRFS_I(inode)->flags & (BTRFS_INODE_NODATACOW | > + BTRFS_INODE_PREALLOC)) { > ret = check_can_nocow(inode, pos, &write_bytes); > - if (ret < 0) > - break; > if (ret > 0) { > - /* > - * For nodata cow case, no need to reserve > - * data space. > - */ > only_release_metadata = true; > /* > * our prealloc extent may be smaller than > @@ -1543,10 +1539,13 @@ static noinline ssize_t __btrfs_buffered_write(struct > file *file, > num_pages = DIV_ROUND_UP(write_bytes + offset, > PAGE_CACHE_SIZE); > reserve_bytes = num_pages << PAGE_CACHE_SHIFT; > + > + ret = 0; > goto reserve_metadata; > + } else { > + ret = -ENOSPC; > } > } > - ret = btrfs_check_data_free_space(inode, pos, write_bytes); > if (ret < 0) > break; > -- With respect, Roman
pgp3t7YZzh4fY.pgp
Description: OpenPGP digital signature
