kernel/linux.git/fs/ext4/mballoc.c, branch v6.1

ext4: fixup possible uninitialized variable access in ext4_mb_choose_next_group_cr1()

2022-09-26T17:21:05+00:00

Variable 'grp' may be left uninitialized if there's no group with suitable average fragment size (or larger). Fix the problem by initializing it earlier. Link: https://lore.kernel.org/r/20220922091542.pkhedytey7wzp5fi@quack3 Fixes: 83e80a6e3543 ("ext4: use buckets for cr 1 block scan instead of rbtree") Cc: stable@kernel.org Reported-by: Dan Carpenter Signed-off-by: Jan Kara Signed-off-by: Theodore Ts'o

ext4: limit the number of retries after discarding preallocations blocks

2022-09-22T14:51:19+00:00

This patch avoids threads live-locking for hours when a large number threads are competing over the last few free extents as they blocks getting added and removed from preallocation pools. From our bug reporter: A reliable way for triggering this has multiple writers continuously write() to files when the filesystem is full, while small amounts of space are freed (e.g. by truncating a large file -1MiB at a time). In the local filesystem, this can be done by simply not checking the return code of write (0) and/or the error (ENOSPACE) that is set. Over NFS with an async mount, even clients with proper error checking will behave this way since the linux NFS client implementation will not propagate the server errors [the write syscalls immediately return success] until the file handle is closed. This leads to a situation where NFS clients send a continuous stream of WRITE rpcs which result in ERRNOSPACE -- but since the client isn't seeing this, the stream of writes continues at maximum network speed. When some space does appear, multiple writers will all attempt to claim it for their current write. For NFS, we may see dozens to hundreds of threads that do this. The real-world scenario of this is database backup tooling (in particular, github.com/mdkent/percona-xtrabackup) which may write large files (>1TiB) to NFS for safe keeping. Some temporary files are written, rewound, and read back -- all before closing the file handle (the temp file is actually unlinked, to trigger automatic deletion on close/crash.) An application like this operating on an async NFS mount will not see an error code until TiB have been written/read. The lockup was observed when running this database backup on large filesystems (64 TiB in this case) with a high number of block groups and no free space. Fragmentation is generally not a factor in this filesystem (~thousands of large files, mostly contiguous except for the parts written while the filesystem is at capacity.) Signed-off-by: Theodore Ts'o Cc: stable@kernel.org

ext4: use buckets for cr 1 block scan instead of rbtree

2022-09-22T02:12:03+00:00

Using rbtree for sorting groups by average fragment size is relatively expensive (needs rbtree update on every block freeing or allocation) and leads to wide spreading of allocations because selection of block group is very sentitive both to changes in free space and amount of blocks allocated. Furthermore selecting group with the best matching average fragment size is not necessary anyway, even more so because the variability of fragment sizes within a group is likely large so average is not telling much. We just need a group with large enough average fragment size so that we have high probability of finding large enough free extent and we don't want average fragment size to be too big so that we are likely to find free extent only somewhat larger than what we need. So instead of maintaing rbtree of groups sorted by fragment size keep bins (lists) or groups where average fragment size is in the interval [2^i, 2^(i+1)). This structure requires less updates on block allocation / freeing, generally avoids chaotic spreading of allocations into block groups, and still is able to quickly (even faster that the rbtree) provide a block group which is likely to have a suitably sized free space extent. This patch reduces number of block groups used when untarring archive with medium sized files (size somewhat above 64k which is default mballoc limit for avoiding locality group preallocation) to about half and thus improves write speeds for eMMC flash significantly. Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") CC: stable@kernel.org Reported-and-tested-by: Stefan Wahren Tested-by: Ojaswin Mujoo Signed-off-by: Jan Kara Reviewed-by: Ritesh Harjani (IBM) Link: https://lore.kernel.org/all/0d81a7c2-46b7-6010-62a4-3e6cfc1628d6@i2se.com/ Link: https://lore.kernel.org/r/20220908092136.11770-5-jack@suse.cz Signed-off-by: Theodore Ts'o

ext4: use locality group preallocation for small closed files

2022-09-22T02:12:00+00:00

Curently we don't use any preallocation when a file is already closed when allocating blocks (from writeback code when converting delayed allocation). However for small files, using locality group preallocation is actually desirable as that is not specific to a particular file. Rather it is a method to pack small files together to reduce fragmentation and for that the fact the file is closed is actually even stronger hint the file would benefit from packing. So change the logic to allow locality group preallocation in this case. Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") CC: stable@kernel.org Reported-and-tested-by: Stefan Wahren Tested-by: Ojaswin Mujoo Reviewed-by: Ritesh Harjani (IBM) Signed-off-by: Jan Kara Link: https://lore.kernel.org/all/0d81a7c2-46b7-6010-62a4-3e6cfc1628d6@i2se.com/ Link: https://lore.kernel.org/r/20220908092136.11770-4-jack@suse.cz Signed-off-by: Theodore Ts'o

ext4: avoid unnecessary spreading of allocations among groups

2022-09-22T02:11:41+00:00

mb_set_largest_free_order() updates lists containing groups with largest chunk of free space of given order. The way it updates it leads to always moving the group to the tail of the list. Thus allocations looking for free space of given order effectively end up cycling through all groups (and due to initialization in last to first order). This spreads allocations among block groups which reduces performance for rotating disks or low-end flash media. Change mb_set_largest_free_order() to only update lists if the order of the largest free chunk in the group changed. Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") CC: stable@kernel.org Reported-and-tested-by: Stefan Wahren Tested-by: Ojaswin Mujoo Reviewed-by: Ritesh Harjani (IBM) Signed-off-by: Jan Kara Link: https://lore.kernel.org/all/0d81a7c2-46b7-6010-62a4-3e6cfc1628d6@i2se.com/ Link: https://lore.kernel.org/r/20220908092136.11770-2-jack@suse.cz Signed-off-by: Theodore Ts'o

ext4: make mballoc try target group first even with mb_optimize_scan

2022-09-22T02:11:34+00:00

One of the side-effects of mb_optimize_scan was that the optimized functions to select next group to try were called even before we tried the goal group. As a result we no longer allocate files close to corresponding inodes as well as we don't try to expand currently allocated extent in the same group. This results in reaim regression with workfile.disk workload of upto 8% with many clients on my test machine: baseline mb_optimize_scan Hmean disk-1 2114.16 ( 0.00%) 2099.37 ( -0.70%) Hmean disk-41 87794.43 ( 0.00%) 83787.47 * -4.56%* Hmean disk-81 148170.73 ( 0.00%) 135527.05 * -8.53%* Hmean disk-121 177506.11 ( 0.00%) 166284.93 * -6.32%* Hmean disk-161 220951.51 ( 0.00%) 207563.39 * -6.06%* Hmean disk-201 208722.74 ( 0.00%) 203235.59 ( -2.63%) Hmean disk-241 222051.60 ( 0.00%) 217705.51 ( -1.96%) Hmean disk-281 252244.17 ( 0.00%) 241132.72 * -4.41%* Hmean disk-321 255844.84 ( 0.00%) 245412.84 * -4.08%* Also this is causing huge regression (time increased by a factor of 5 or so) when untarring archive with lots of small files on some eMMC storage cards. Fix the problem by making sure we try goal group first. Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning") CC: stable@kernel.org Reported-and-tested-by: Stefan Wahren Tested-by: Ojaswin Mujoo Reviewed-by: Ritesh Harjani (IBM) Link: https://lore.kernel.org/all/20220727105123.ckwrhbilzrxqpt24@quack3/ Link: https://lore.kernel.org/all/0d81a7c2-46b7-6010-62a4-3e6cfc1628d6@i2se.com/ Signed-off-by: Jan Kara Link: https://lore.kernel.org/r/20220908092136.11770-1-jack@suse.cz Signed-off-by: Theodore Ts'o

ext4: block range must be validated before use in ext4_mb_clear_bb()

2022-08-03T03:56:25+00:00

Block range to free is validated in ext4_free_blocks() using ext4_inode_block_valid() and then it's passed to ext4_mb_clear_bb(). However in some situations on bigalloc file system the range might be adjusted after the validation in ext4_free_blocks() which can lead to troubles on corrupted file systems such as one found by syzkaller that resulted in the following BUG kernel BUG at fs/ext4/ext4.h:3319! PREEMPT SMP NOPTI CPU: 28 PID: 4243 Comm: repro Kdump: loaded Not tainted 5.19.0-rc6+ #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014 RIP: 0010:ext4_free_blocks+0x95e/0xa90 Call Trace: ? lock_timer_base+0x61/0x80 ? __es_remove_extent+0x5a/0x760 ? __mod_timer+0x256/0x380 ? ext4_ind_truncate_ensure_credits+0x90/0x220 ext4_clear_blocks+0x107/0x1b0 ext4_free_data+0x15b/0x170 ext4_ind_truncate+0x214/0x2c0 ? _raw_spin_unlock+0x15/0x30 ? ext4_discard_preallocations+0x15a/0x410 ? ext4_journal_check_start+0xe/0x90 ? __ext4_journal_start_sb+0x2f/0x110 ext4_truncate+0x1b5/0x460 ? __ext4_journal_start_sb+0x2f/0x110 ext4_evict_inode+0x2b4/0x6f0 evict+0xd0/0x1d0 ext4_enable_quotas+0x11f/0x1f0 ext4_orphan_cleanup+0x3de/0x430 ? proc_create_seq_private+0x43/0x50 ext4_fill_super+0x295f/0x3ae0 ? snprintf+0x39/0x40 ? sget_fc+0x19c/0x330 ? ext4_reconfigure+0x850/0x850 get_tree_bdev+0x16d/0x260 vfs_get_tree+0x25/0xb0 path_mount+0x431/0xa70 __x64_sys_mount+0xe2/0x120 do_syscall_64+0x5b/0x80 ? do_user_addr_fault+0x1e2/0x670 ? exc_page_fault+0x70/0x170 entry_SYSCALL_64_after_hwframe+0x46/0xb0 RIP: 0033:0x7fdf4e512ace Fix it by making sure that the block range is properly validated before used every time it changes in ext4_free_blocks() or ext4_mb_clear_bb(). Link: https://syzkaller.appspot.com/bug?id=5266d464285a03cee9dbfda7d2452a72c3c2ae7c Reported-by: syzbot+15cd994e273307bf5cfa@syzkaller.appspotmail.com Signed-off-by: Lukas Czerner Cc: Tadeusz Struk Tested-by: Tadeusz Struk Link: https://lore.kernel.org/r/20220714165903.58260-1-lczerner@redhat.com Signed-off-by: Theodore Ts'o

ext4: reuse order and buddy in mb_mark_used when buddy split

2022-08-03T03:52:19+00:00

After each buddy split, mb_mark_used will search the proper order for the block which may consume some loop in mb_find_order_for_block. In fact, we can reuse the order and buddy generated by the buddy split. Reviewed by: lei.rao@intel.com Signed-off-by: hanjinke Link: https://lore.kernel.org/r/20220606155305.74146-1-hanjinke.666@bytedance.com Signed-off-by: Theodore Ts'o

ext4: correct the judgment of BUG in ext4_mb_normalize_request

2022-06-18T23:35:57+00:00

ext4_mb_normalize_request() can move logical start of allocated blocks to reduce fragmentation and better utilize preallocation. However logical block requested as a start of allocation (ac->ac_o_ex.fe_logical) should always be covered by allocated blocks so we should check that by modifying and to or in the assertion. Signed-off-by: Baokun Li Reviewed-by: Ritesh Harjani Link: https://lore.kernel.org/r/20220528110017.354175-3-libaokun1@huawei.com Signed-off-by: Theodore Ts'o

ext4: fix bug_on ext4_mb_use_inode_pa

2022-06-18T23:35:43+00:00

Hulk Robot reported a BUG_ON: ================================================================== kernel BUG at fs/ext4/mballoc.c:3211! [...] RIP: 0010:ext4_mb_mark_diskspace_used.cold+0x85/0x136f [...] Call Trace: ext4_mb_new_blocks+0x9df/0x5d30 ext4_ext_map_blocks+0x1803/0x4d80 ext4_map_blocks+0x3a4/0x1a10 ext4_writepages+0x126d/0x2c30 do_writepages+0x7f/0x1b0 __filemap_fdatawrite_range+0x285/0x3b0 file_write_and_wait_range+0xb1/0x140 ext4_sync_file+0x1aa/0xca0 vfs_fsync_range+0xfb/0x260 do_fsync+0x48/0xa0 [...] ================================================================== Above issue may happen as follows: ------------------------------------- do_fsync vfs_fsync_range ext4_sync_file file_write_and_wait_range __filemap_fdatawrite_range do_writepages ext4_writepages mpage_map_and_submit_extent mpage_map_one_extent ext4_map_blocks ext4_mb_new_blocks ext4_mb_normalize_request >>> start + size <= ac->ac_o_ex.fe_logical ext4_mb_regular_allocator ext4_mb_simple_scan_group ext4_mb_use_best_found ext4_mb_new_preallocation ext4_mb_new_inode_pa ext4_mb_use_inode_pa >>> set ac->ac_b_ex.fe_len <= 0 ext4_mb_mark_diskspace_used >>> BUG_ON(ac->ac_b_ex.fe_len <= 0); we can easily reproduce this problem with the following commands: `fallocate -l100M disk` `mkfs.ext4 -b 1024 -g 256 disk` `mount disk /mnt` `fsstress -d /mnt -l 0 -n 1000 -p 1` The size must be smaller than or equal to EXT4_BLOCKS_PER_GROUP. Therefore, "start + size <= ac->ac_o_ex.fe_logical" may occur when the size is truncated. So start should be the start position of the group where ac_o_ex.fe_logical is located after alignment. In addition, when the value of fe_logical or EXT4_BLOCKS_PER_GROUP is very large, the value calculated by start_off is more accurate. Cc: stable@kernel.org Fixes: cd648b8a8fd5 ("ext4: trim allocation requests to group size") Reported-by: Hulk Robot Signed-off-by: Baokun Li Reviewed-by: Ritesh Harjani Link: https://lore.kernel.org/r/20220528110017.354175-2-libaokun1@huawei.com Signed-off-by: Theodore Ts'o