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27 March 2024, 02:37:15 UTC
Revision 99b7db7b8ffd6bb755eb0a175596421a0b581cb2 authored by Nick Piggin on 17 August 2010, 18:37:39 UTC, committed by Al Viro on 18 August 2010, 12:35:48 UTC 
fs: brlock vfsmount_lock
 
fs: brlock vfsmount_lock

Use a brlock for the vfsmount lock. It must be taken for write whenever
modifying the mount hash or associated fields, and may be taken for read when
performing mount hash lookups.

A new lock is added for the mnt-id allocator, so it doesn't need to take
the heavy vfsmount write-lock.

The number of atomics should remain the same for fastpath rlock cases, though
code would be slightly slower due to per-cpu access. Scalability is not not be
much improved in common cases yet, due to other locks (ie. dcache_lock) getting
in the way. However path lookups crossing mountpoints should be one case where
scalability is improved (currently requiring the global lock).

The slowpath is slower due to use of brlock. On a 64 core, 64 socket, 32 node
Altix system (high latency to remote nodes), a simple umount microbenchmark
(mount --bind mnt mnt2 ; umount mnt2 loop 1000 times), before this patch it
took 6.8s, afterwards took 7.1s, about 5% slower.

Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
1 parent 6416ccb
History
Tip revision: 99b7db7b8ffd6bb755eb0a175596421a0b581cb2 authored by Nick Piggin on 17 August 2010, 18:37:39 UTC
fs: brlock vfsmount_lock
Tip revision: 99b7db7
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