On 04/12/2012 11:54 PM, Arne Jansen wrote: > This patchset reimplements snapshot deletion with the help of the readahead > framework. For this callbacks are added to the framework. The main idea is > to traverse many snapshots at once at read many branches at once. This way > readahead get many requests at once (currently about 50000), giving it the > chance to order disk accesses properly. On a single disk, the effect is > currently spoiled by sync operations that still take place, mainly checksum > deletion. The most benefit can be gained with multiple devices, as all devices > can be fully utilized. It scales quite well with the number of devices. > For more details see the commit messages of the individual patches and the > source code comments. > > How it is tested: > I created a test volume using David Sterba's stress-subvol-git-aging.sh. It > checks out randoms version of the kernel git tree, creating a snapshot from it > from time to time and checks out other versions there, and so on. In the end > the fs had 80 subvols with various degrees of sharing between them. The > following tests were conducted on it: > - delete a subvol using droptree and check the fs with btrfsck afterwards > for consistency > - delete all subvols and verify with btrfs-debug-tree that the extent > allocation tree is clean > - delete 70 subvols, and in parallel empty the other 10 with rm -rf to get > a good pressure on locking > - add various degrees of memory pressure to the previous test to get pages > to expire early from page cache > - enable all relevant kernel debugging options during all tests > > The performance gain on a single drive was about 20%, on 8 drives about 600%. > It depends vastly on the maximum parallelity of the readahead, that is > currently hardcoded to about 50000. This number is subject to 2 factors, the > available RAM and the size of the saved state for a commit. As the full state > has to be saved on commit, a large parallelity leads to a large state. > > Based on this I'll see if I can add delayed checksum deletions and running > the delayed refs via readahead, to gain a maximum ordering of I/O ops. > Hi Arne, Can you please show us some user cases in this, or can we get some extra benefits from it? :) thanks, liubo > This patchset is also available at > > git://git.kernel.org/pub/scm/linux/kernel/git/arne/linux-btrfs.git droptree > > Arne Jansen (5): > btrfs: extend readahead interface > btrfs: add droptree inode > btrfs: droptree structures and initialization > btrfs: droptree implementation > btrfs: use droptree for snapshot deletion > > fs/btrfs/Makefile | 2 +- > fs/btrfs/btrfs_inode.h | 4 + > fs/btrfs/ctree.h | 78 ++- > fs/btrfs/disk-io.c | 19 + > fs/btrfs/droptree.c | 1916 +++++++++++++++++++++++++++++++++++++++++++ > fs/btrfs/free-space-cache.c | 131 +++- > fs/btrfs/free-space-cache.h | 32 + > fs/btrfs/inode.c | 3 +- > fs/btrfs/reada.c | 494 +++++++++--- > fs/btrfs/scrub.c | 29 +- > fs/btrfs/transaction.c | 35 +- > 11 files changed, 2592 insertions(+), 151 deletions(-) > create mode 100644 fs/btrfs/droptree.c > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
