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linux/fs/btrfs/free-space-cache.h

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Btrfs: rework allocation clustering Because btrfs is copy-on-write, we end up picking new locations for blocks very often. This makes it fairly difficult to maintain perfect read patterns over time, but we can at least do some optimizations for writes. This is done today by remembering the last place we allocated and trying to find a free space hole big enough to hold more than just one allocation. The end result is that we tend to write sequentially to the drive. This happens all the time for metadata and it happens for data when mounted -o ssd. But, the way we record it is fairly racey and it tends to fragment the free space over time because we are trying to allocate fairly large areas at once. This commit gets rid of the races by adding a free space cluster object with dedicated locking to make sure that only one process at a time is out replacing the cluster. The free space fragmentation is somewhat solved by allowing a cluster to be comprised of smaller free space extents. This part definitely adds some CPU time to the cluster allocations, but it allows the allocator to consume the small holes left behind by cow. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-04-03 06:47:43 -07:00
/*
* Copyright (C) 2009 Oracle. All rights reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public
* License v2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public
* License along with this program; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 021110-1307, USA.
*/
#ifndef __BTRFS_FREE_SPACE_CACHE
#define __BTRFS_FREE_SPACE_CACHE
Btrfs: use hybrid extents+bitmap rb tree for free space Currently btrfs has a problem where it can use a ridiculous amount of RAM simply tracking free space. As free space gets fragmented, we end up with thousands of entries on an rb-tree per block group, which usually spans 1 gig of area. Since we currently don't ever flush free space cache back to disk this gets to be a bit unweildly on large fs's with lots of fragmentation. This patch solves this problem by using PAGE_SIZE bitmaps for parts of the free space cache. Initially we calculate a threshold of extent entries we can handle, which is however many extent entries we can cram into 16k of ram. The maximum amount of RAM that should ever be used to track 1 gigabyte of diskspace will be 32k of RAM, which scales much better than we did before. Once we pass the extent threshold, we start adding bitmaps and using those instead for tracking the free space. This patch also makes it so that any free space thats less than 4 * sectorsize we go ahead and put into a bitmap. This is nice since we try and allocate out of the front of a block group, so if the front of a block group is heavily fragmented and then has a huge chunk of free space at the end, we go ahead and add the fragmented areas to bitmaps and use a normal extent entry to track the big chunk at the back of the block group. I've also taken the opportunity to revamp how we search for free space. Previously we indexed free space via an offset indexed rb tree and a bytes indexed rb tree. I've dropped the bytes indexed rb tree and use only the offset indexed rb tree. This cuts the number of tree operations we were doing previously down by half, and gives us a little bit of a better allocation pattern since we will always start from a specific offset and search forward from there, instead of searching for the size we need and try and get it as close as possible to the offset we want. I've given this a healthy amount of testing pre-new format stuff, as well as post-new format stuff. I've booted up my fedora box which is installed on btrfs with this patch and ran with it for a few days without issues. I've not seen any performance regressions in any of my tests. Since the last patch Yan Zheng fixed a problem where we could have overlapping entries, so updating their offset inline would cause problems. Thanks, Signed-off-by: Josef Bacik <jbacik@redhat.com> Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-07-13 18:29:25 -07:00
struct btrfs_free_space {
struct rb_node offset_index;
u64 offset;
u64 bytes;
unsigned long *bitmap;
struct list_head list;
};
Btrfs: rework allocation clustering Because btrfs is copy-on-write, we end up picking new locations for blocks very often. This makes it fairly difficult to maintain perfect read patterns over time, but we can at least do some optimizations for writes. This is done today by remembering the last place we allocated and trying to find a free space hole big enough to hold more than just one allocation. The end result is that we tend to write sequentially to the drive. This happens all the time for metadata and it happens for data when mounted -o ssd. But, the way we record it is fairly racey and it tends to fragment the free space over time because we are trying to allocate fairly large areas at once. This commit gets rid of the races by adding a free space cluster object with dedicated locking to make sure that only one process at a time is out replacing the cluster. The free space fragmentation is somewhat solved by allowing a cluster to be comprised of smaller free space extents. This part definitely adds some CPU time to the cluster allocations, but it allows the allocator to consume the small holes left behind by cow. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-04-03 06:47:43 -07:00
int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
u64 bytenr, u64 size);
int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
u64 bytenr, u64 size);
void btrfs_remove_free_space_cache(struct btrfs_block_group_cache
*block_group);
u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
u64 offset, u64 bytes, u64 empty_size);
void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
u64 bytes);
u64 btrfs_block_group_free_space(struct btrfs_block_group_cache *block_group);
int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
Btrfs: add mount -o ssd_spread to spread allocations out Some SSDs perform best when reusing block numbers often, while others perform much better when clustering strictly allocates big chunks of unused space. The default mount -o ssd will find rough groupings of blocks where there are a bunch of free blocks that might have some allocated blocks mixed in. mount -o ssd_spread will make sure there are no allocated blocks mixed in. It should perform better on lower end SSDs. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-06-09 17:28:34 -07:00
struct btrfs_root *root,
Btrfs: rework allocation clustering Because btrfs is copy-on-write, we end up picking new locations for blocks very often. This makes it fairly difficult to maintain perfect read patterns over time, but we can at least do some optimizations for writes. This is done today by remembering the last place we allocated and trying to find a free space hole big enough to hold more than just one allocation. The end result is that we tend to write sequentially to the drive. This happens all the time for metadata and it happens for data when mounted -o ssd. But, the way we record it is fairly racey and it tends to fragment the free space over time because we are trying to allocate fairly large areas at once. This commit gets rid of the races by adding a free space cluster object with dedicated locking to make sure that only one process at a time is out replacing the cluster. The free space fragmentation is somewhat solved by allowing a cluster to be comprised of smaller free space extents. This part definitely adds some CPU time to the cluster allocations, but it allows the allocator to consume the small holes left behind by cow. Signed-off-by: Chris Mason <chris.mason@oracle.com>
2009-04-03 06:47:43 -07:00
struct btrfs_block_group_cache *block_group,
struct btrfs_free_cluster *cluster,
u64 offset, u64 bytes, u64 empty_size);
void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster);
u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
struct btrfs_free_cluster *cluster, u64 bytes,
u64 min_start);
int btrfs_return_cluster_to_free_space(
struct btrfs_block_group_cache *block_group,
struct btrfs_free_cluster *cluster);
#endif
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