BMC/Intel-BMC/linux.git/fs/btrfs/free-space-cache.h, branch dev

Btrfs: allow block group cache writeout outside critical section in commit

2015-04-10T21:07:22+00:00

We loop through all of the dirty block groups during commit and write the free space cache. In order to make sure the cache is currect, we do this while no other writers are allowed in the commit. If a large number of block groups are dirty, this can introduce long stalls during the final stages of the commit, which can block new procs trying to change the filesystem. This commit changes the block group cache writeout to take appropriate locks and allow it to run earlier in the commit. We'll still have to redo some of the block groups, but it means we can get most of the work out of the way without blocking the entire FS. Signed-off-by: Chris Mason

Btrfs: two stage dirty block group writeout

2015-04-10T21:07:11+00:00

Block group cache writeout is currently waiting on the pages for each block group cache before moving on to writing the next one. This commit switches things around to send down all the caches and then wait on them in batches. The end result is much faster, since we're keeping the disk pipeline full. Signed-off-by: Chris Mason

Btrfs: fix race between writing free space cache and trimming

2014-12-03T02:35:09+00:00

Trimming is completely transactionless, and the way it operates consists of hiding free space entries from a block group, perform the trim/discard and then make the free space entries visible again. Therefore while a free space entry is being trimmed, we can have free space cache writing running in parallel (as part of a transaction commit) which will miss the free space entry. This means that an unmount (or crash/reboot) after that transaction commit and mount again before another transaction starts/commits after the discard finishes, we will have some free space that won't be used again unless the free space cache is rebuilt. After the unmount, fsck (btrfsck, btrfs check) reports the issue like the following example: *** fsck.btrfs output *** checking extents checking free space cache There is no free space entry for 521764864-521781248 There is no free space entry for 521764864-1103101952 cache appears valid but isnt 29360128 Checking filesystem on /dev/sdc UUID: b4789e27-4774-4626-98e9-ae8dfbfb0fb5 found 1235681286 bytes used err is -22 (...) Another issue caused by this race is a crash while writing bitmap entries to the cache, because while the cache writeout task accesses the bitmaps, the trim task can be concurrently modifying the bitmap or worse might be freeing the bitmap. The later case results in the following crash: [55650.804460] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC [55650.804835] Modules linked in: btrfs dm_flakey dm_mod crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd fscache sunrpc loop parport_pc parport i2c_piix4 psmouse evdev pcspkr microcode processor i2ccore serio_raw thermal_sys button ext4 crc16 jbd2 mbcache sg sd_mod crc_t10dif sr_mod cdrom crct10dif_generic crct10dif_common ata_generic virtio_scsi floppy ata_piix libata virtio_pci virtio_ring virtio scsi_mod e1000 [last unloaded: btrfs] [55650.806169] CPU: 1 PID: 31002 Comm: btrfs-transacti Tainted: G W 3.17.0-rc5-btrfs-next-1+ #1 [55650.806493] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [55650.806867] task: ffff8800b12f6410 ti: ffff880071538000 task.ti: ffff880071538000 [55650.807166] RIP: 0010:[] [] write_bitmap_entries+0x65/0xbb [btrfs] [55650.807514] RSP: 0018:ffff88007153bc30 EFLAGS: 00010246 [55650.807687] RAX: 000000005d1ec000 RBX: ffff8800a665df08 RCX: 0000000000000400 [55650.807885] RDX: ffff88005d1ec000 RSI: 6b6b6b6b6b6b6b6b RDI: ffff88005d1ec000 [55650.808017] RBP: ffff88007153bc58 R08: 00000000ddd51536 R09: 00000000000001e0 [55650.808017] R10: 0000000000000000 R11: 0000000000000037 R12: 6b6b6b6b6b6b6b6b [55650.808017] R13: ffff88007153bca8 R14: 6b6b6b6b6b6b6b6b R15: ffff88007153bc98 [55650.808017] FS: 0000000000000000(0000) GS:ffff88023ec80000(0000) knlGS:0000000000000000 [55650.808017] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [55650.808017] CR2: 0000000002273b88 CR3: 00000000b18f6000 CR4: 00000000000006e0 [55650.808017] Stack: [55650.808017] ffff88020e834e00 ffff880172d68db0 0000000000000000 ffff88019257c800 [55650.808017] ffff8801d42ea720 ffff88007153bd10 ffffffffa037d2fa ffff880224e99180 [55650.808017] ffff8801469a6188 ffff880224e99140 ffff880172d68c50 00000003000000b7 [55650.808017] Call Trace: [55650.808017] [] __btrfs_write_out_cache+0x1ea/0x37f [btrfs] [55650.808017] [] btrfs_write_out_cache+0xa1/0xd8 [btrfs] [55650.808017] [] btrfs_write_dirty_block_groups+0x4b5/0x505 [btrfs] [55650.808017] [] commit_cowonly_roots+0x15e/0x1f7 [btrfs] [55650.808017] [] ? _raw_spin_lock+0xe/0x10 [55650.808017] [] btrfs_commit_transaction+0x411/0x882 [btrfs] [55650.808017] [] transaction_kthread+0xf2/0x1a4 [btrfs] [55650.808017] [] ? btrfs_cleanup_transaction+0x3d8/0x3d8 [btrfs] [55650.808017] [] kthread+0xb7/0xbf [55650.808017] [] ? __kthread_parkme+0x67/0x67 [55650.808017] [] ret_from_fork+0x7c/0xb0 [55650.808017] [] ? __kthread_parkme+0x67/0x67 [55650.808017] Code: 4c 89 ef 8d 70 ff e8 d4 fc ff ff 41 8b 45 34 41 39 45 30 7d 5c 31 f6 4c 89 ef e8 80 f6 ff ff 49 8b 7d 00 4c 89 f6 b9 00 04 00 00 a5 4c 89 ef 41 8b 45 30 8d 70 ff e8 a3 fc ff ff 41 8b 45 34 [55650.808017] RIP [] write_bitmap_entries+0x65/0xbb [btrfs] [55650.808017] RSP [55650.815725] ---[ end trace 1c032e96b149ff86 ]--- Fix this by serializing both tasks in such a way that cache writeout doesn't wait for the trim/discard of free space entries to finish and doesn't miss any free space entry. Signed-off-by: Filipe Manana Signed-off-by: Chris Mason

Btrfs: remove path arg from btrfs_truncate_free_space_cache

2013-11-12T02:51:33+00:00

Not used for anything, and removing it avoids caller's need to allocate a path structure. Signed-off-by: Filipe David Borba Manana Signed-off-by: Josef Bacik Signed-off-by: Chris Mason

Btrfs: remove duplicated ino cache's inode lookup

2013-11-12T02:51:24+00:00

We're doing a unnecessary extra lookup of the ino cache's inode when we already have it (and holding a reference) during the process of saving the ino cache contents to disk. Therefore remove this extra lookup. Signed-off-by: Filipe David Borba Manana Signed-off-by: Josef Bacik Signed-off-by: Chris Mason

Btrfs: allocate the free space by the existed max extent size when ENOSPC

2013-09-21T15:05:23+00:00

By the current code, if the requested size is very large, and all the extents in the free space cache are small, we will waste lots of the cpu time to cut the requested size in half and search the cache again and again until it gets down to the size the allocator can return. In fact, we can know the max extent size in the cache after the first search, so we needn't cut the size in half repeatedly, and just use the max extent size directly. This way can save lots of cpu time and make the performance grow up when there are only fragments in the free space cache. According to my test, if there are only 4KB free space extents in the fs, and the total size of those extents are 256MB, we can reduce the execute time of the following test from 5.4s to 1.4s. dd if=/dev/zero of= bs=1MB count=1 oflag=sync Changelog v2 -> v3: - fix the problem that we skip the block group with the space which is less than we need. Changelog v1 -> v2: - address the problem that we return a wrong start position when searching the free space in a bitmap. Signed-off-by: Miao Xie Signed-off-by: Josef Bacik Signed-off-by: Chris Mason

Btrfs: separate out tests into their own directory

2013-09-01T12:15:38+00:00

The plan is to have a bunch of unit tests that run when btrfs is loaded when you build with the appropriate config option. My ultimate goal is to have a test for every non-static function we have, but at first I'm going to focus on the things that cause us the most problems. To start out with this just adds a tests/ directory and moves the existing free space cache tests into that directory and sets up all of the infrastructure. Thanks, Signed-off-by: Josef Bacik Signed-off-by: Chris Mason

Btrfs: avoid starting a transaction in the write path

2013-09-01T12:05:05+00:00

I noticed while looking at a deadlock that we are always starting a transaction in cow_file_range(). This isn't really needed since we only need a transaction if we are doing an inline extent, or if the allocator needs to allocate a chunk. So push down all the transaction start stuff to be closer to where we actually need a transaction in all of these cases. This will hopefully reduce our write latency when we are committing often. Thanks, Signed-off-by: Josef Bacik Signed-off-by: Chris Mason

btrfs: move ifdef around sanity checks out of init_btrfs_fs

2013-06-14T15:29:18+00:00

Signed-off-by: David Sterba Signed-off-by: Josef Bacik

Btrfs: don't use global block reservation for inode cache truncation

2013-05-18T01:40:22+00:00

It is very likely that there are lots of subvolumes/snapshots in the filesystem, so if we use global block reservation to do inode cache truncation, we may hog all the free space that is reserved in global rsv. So it is better that we do the free space reservation for inode cache truncation by ourselves. Cc: Tsutomu Itoh Signed-off-by: Miao Xie Signed-off-by: Josef Bacik