On Thu, Sep 30, 2010 at 07:28:05PM +0200, Eric Dumazet wrote: > 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 Thanks Eric, this looks good. You didn't seem to add a comment about preempt safety that Andrew wanted, but I'll add it. > > 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@xxxxxxxxx> > Signed-off-by: Nick Piggin <npiggin@xxxxxxx> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > --- > 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); > } > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html