Messages in this thread Patch in this message | | | Subject | Re: [PATCH] fs: inode per-cpu last_ino allocator | From | Eric Dumazet <> | Date | Thu, 30 Sep 2010 19:28:05 +0200 |
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Le jeudi 30 septembre 2010 à 09:45 -0700, Andrew Morton a écrit :
> Could eliminate `p' I guess, but that would involve using > __get_cpu_var() as an lval, which looks vile and might generate worse > code. >
Hmm, I see, please check this new patch, using the most modern stuff ;)
> Readers of this code won't know why last_ino_get() was marked noinline. > It looks wrong, really.
Oops sorry, this was a temporary hack of mine to ease disassembly analysis. Good catch !
Here is the new generated code on i686 (with the noinline) : pretty good ;)
c02e5930 <last_ino_get>: c02e5930: 55 push %ebp c02e5931: 89 e5 mov %esp,%ebp c02e5933: 64 a1 44 29 7d c0 mov %fs:0xc07d2944,%eax c02e5939: a9 ff 03 00 00 test $0x3ff,%eax c02e593e: 74 09 je c02e5949 <last_ino_get+0x19> c02e5940: 40 inc %eax c02e5941: 64 a3 44 29 7d c0 mov %eax,%fs:0xc07d2944 c02e5947: c9 leave c02e5948: c3 ret c02e5949: b8 00 04 00 00 mov $0x400,%eax c02e594e: f0 0f c1 05 80 c8 92 c0 lock xadd %eax,0xc092c880 c02e5956: eb e8 jmp c02e5940 <last_ino_get+0x10>
Thanks
[PATCH] fs: inode per-cpu last_ino allocator
new_inode() dirties a contended cache line to get increasing inode numbers.
Solve this problem by providing to each cpu a per_cpu variable, feeded by the shared last_ino, but once every 1024 allocations. This reduces contention on the shared last_ino, and give same spreading ino numbers than before (i.e. same wraparound after 2^32 allocations).
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Dave Chinner <dchinner@redhat.com> --- fs/inode.c | 47 ++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 40 insertions(+), 7 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c index 8646433..5c233f0 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -624,6 +624,45 @@ void inode_add_to_lists(struct super_block *sb, struct inode *inode) } EXPORT_SYMBOL_GPL(inode_add_to_lists); +#define LAST_INO_BATCH 1024 + +/* + * Each cpu owns a range of LAST_INO_BATCH numbers. + * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations, + * to renew the exhausted range. + * + * This does not significantly increase overflow rate because every CPU can + * consume at most LAST_INO_BATCH-1 unused inode numbers. So there is + * NR_CPUS*(LAST_INO_BATCH-1) wastage. At 4096 and 1024, this is ~0.1% of the + * 2^32 range, and is a worst-case. Even a 50% wastage would only increase + * overflow rate by 2x, which does not seem too significant. + * + * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW + * error if st_ino won't fit in target struct field. Use 32bit counter + * here to attempt to avoid that. + */ +static DEFINE_PER_CPU(unsigned int, last_ino); + +static unsigned int last_ino_get(void) +{ + unsigned int res; + + get_cpu(); + res = __this_cpu_read(last_ino); +#ifdef CONFIG_SMP + if (unlikely((res & (LAST_INO_BATCH - 1)) == 0)) { + static atomic_t shared_last_ino; + int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino); + + res = next - LAST_INO_BATCH; + } +#endif + res++; + __this_cpu_write(last_ino, res); + put_cpu(); + return res; +} + /** * new_inode - obtain an inode * @sb: superblock @@ -638,12 +677,6 @@ EXPORT_SYMBOL_GPL(inode_add_to_lists); */ struct inode *new_inode(struct super_block *sb) { - /* - * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW - * error if st_ino won't fit in target struct field. Use 32bit counter - * here to attempt to avoid that. - */ - static unsigned int last_ino; struct inode *inode; spin_lock_prefetch(&inode_lock); @@ -652,7 +685,7 @@ struct inode *new_inode(struct super_block *sb) if (inode) { spin_lock(&inode_lock); __inode_add_to_lists(sb, NULL, inode); - inode->i_ino = ++last_ino; + inode->i_ino = last_ino_get(); inode->i_state = 0; spin_unlock(&inode_lock); }
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