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88e0fbc452
We have had a report of bad memory allocation latency during DVD-RAM (UDF) writing. This is causing the user's desktop session to become unusable. Jan tracked the cause of this down to UDF inode reclaim blocking: gnome-screens D ffff810006d1d598 0 20686 1 ffff810006d1d508 0000000000000082 ffff810037db6718 0000000000000800 ffff810006d1d488 ffffffff807e4280 ffffffff807e4280 ffff810006d1a580 ffff8100bccbc140 ffff810006d1a8c0 0000000006d1d4e8 ffff810006d1a8c0 Call Trace: [<ffffffff804477f3>] io_schedule+0x63/0xa5 [<ffffffff802c2587>] sync_buffer+0x3b/0x3f [<ffffffff80447d2a>] __wait_on_bit+0x47/0x79 [<ffffffff80447dc6>] out_of_line_wait_on_bit+0x6a/0x77 [<ffffffff802c24f6>] __wait_on_buffer+0x1f/0x21 [<ffffffff802c442a>] __bread+0x70/0x86 [<ffffffff88de9ec7>] :udf:udf_tread+0x38/0x3a [<ffffffff88de0fcf>] :udf:udf_update_inode+0x4d/0x68c [<ffffffff88de26e1>] :udf:udf_write_inode+0x1d/0x2b [<ffffffff802bcf85>] __writeback_single_inode+0x1c0/0x394 [<ffffffff802bd205>] write_inode_now+0x7d/0xc4 [<ffffffff88de2e76>] :udf:udf_clear_inode+0x3d/0x53 [<ffffffff802b39ae>] clear_inode+0xc2/0x11b [<ffffffff802b3ab1>] dispose_list+0x5b/0x102 [<ffffffff802b3d35>] shrink_icache_memory+0x1dd/0x213 [<ffffffff8027ede3>] shrink_slab+0xe3/0x158 [<ffffffff8027fbab>] try_to_free_pages+0x177/0x232 [<ffffffff8027a578>] __alloc_pages+0x1fa/0x392 [<ffffffff802951fa>] alloc_page_vma+0x176/0x189 [<ffffffff802822d8>] __do_fault+0x10c/0x417 [<ffffffff80284232>] handle_mm_fault+0x466/0x940 [<ffffffff8044b922>] do_page_fault+0x676/0xabf This blocks with iprune_mutex held, which then blocks other reclaimers: X D ffff81009d47c400 0 17285 14831 ffff8100844f3728 0000000000000086 0000000000000000 ffff81000000e288 ffff81000000da00 ffffffff807e4280 ffffffff807e4280 ffff81009d47c400 ffffffff805ff890 ffff81009d47c740 00000000844f3808 ffff81009d47c740 Call Trace: [<ffffffff80447f8c>] __mutex_lock_slowpath+0x72/0xa9 [<ffffffff80447e1a>] mutex_lock+0x1e/0x22 [<ffffffff802b3ba1>] shrink_icache_memory+0x49/0x213 [<ffffffff8027ede3>] shrink_slab+0xe3/0x158 [<ffffffff8027fbab>] try_to_free_pages+0x177/0x232 [<ffffffff8027a578>] __alloc_pages+0x1fa/0x392 [<ffffffff8029507f>] alloc_pages_current+0xd1/0xd6 [<ffffffff80279ac0>] __get_free_pages+0xe/0x4d [<ffffffff802ae1b7>] __pollwait+0x5e/0xdf [<ffffffff8860f2b4>] :nvidia:nv_kern_poll+0x2e/0x73 [<ffffffff802ad949>] do_select+0x308/0x506 [<ffffffff802adced>] core_sys_select+0x1a6/0x254 [<ffffffff802ae0b7>] sys_select+0xb5/0x157 Now I think the main problem is having the filesystem block (and do IO) in inode reclaim. The problem is that this doesn't get accounted well and penalizes a random allocator with a big latency spike caused by work generated from elsewhere. I think the best idea would be to avoid this. By design if possible, or by deferring the hard work to an asynchronous context. If the latter, then the fs would probably want to throttle creation of new work with queue size of the deferred work, but let's not get into those details. Anyway, the other obvious thing we looked at is the iprune_mutex which is causing the cascading blocking. We could turn this into an rwsem to improve concurrency. It is unreasonable to totally ban all potentially slow or blocking operations in inode reclaim, so I think this is a cheap way to get a small improvement. This doesn't solve the whole problem of course. The process doing inode reclaim will still take the latency hit, and concurrent processes may end up contending on filesystem locks. So fs developers should keep these problems in mind. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Jan Kara <jack@ucw.cz> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| lockd | ||
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| nilfs2 | ||
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| notify | ||
| ntfs | ||
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| omfs | ||
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| partitions | ||
| proc | ||
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| squashfs | ||
| sysfs | ||
| sysv | ||
| ubifs | ||
| udf | ||
| ufs | ||
| xfs | ||
| aio.c | ||
| anon_inodes.c | ||
| attr.c | ||
| bad_inode.c | ||
| binfmt_aout.c | ||
| binfmt_elf.c | ||
| binfmt_elf_fdpic.c | ||
| binfmt_em86.c | ||
| binfmt_flat.c | ||
| binfmt_misc.c | ||
| binfmt_script.c | ||
| binfmt_som.c | ||
| bio-integrity.c | ||
| bio.c | ||
| block_dev.c | ||
| buffer.c | ||
| char_dev.c | ||
| compat.c | ||
| compat_binfmt_elf.c | ||
| compat_ioctl.c | ||
| dcache.c | ||
| dcookies.c | ||
| direct-io.c | ||
| drop_caches.c | ||
| eventfd.c | ||
| eventpoll.c | ||
| exec.c | ||
| fcntl.c | ||
| fifo.c | ||
| file.c | ||
| file_table.c | ||
| filesystems.c | ||
| fs-writeback.c | ||
| fs_struct.c | ||
| generic_acl.c | ||
| inode.c | ||
| internal.h | ||
| ioctl.c | ||
| ioprio.c | ||
| Kconfig | ||
| Kconfig.binfmt | ||
| libfs.c | ||
| locks.c | ||
| Makefile | ||
| mbcache.c | ||
| mpage.c | ||
| namei.c | ||
| namespace.c | ||
| nfsctl.c | ||
| no-block.c | ||
| open.c | ||
| pipe.c | ||
| pnode.c | ||
| pnode.h | ||
| posix_acl.c | ||
| read_write.c | ||
| read_write.h | ||
| readdir.c | ||
| select.c | ||
| seq_file.c | ||
| signalfd.c | ||
| splice.c | ||
| stack.c | ||
| stat.c | ||
| super.c | ||
| sync.c | ||
| timerfd.c | ||
| utimes.c | ||
| xattr.c | ||
| xattr_acl.c | ||