From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH] fs: inode per-cpu last_ino allocator Date: Thu, 30 Sep 2010 19:28:05 +0200 Message-ID: <1285867685.2615.865.camel@edumazet-laptop> References: <1285762729-17928-1-git-send-email-david@fromorbit.com> <1285762729-17928-16-git-send-email-david@fromorbit.com> <20100929215312.5fcb6976.akpm@linux-foundation.org> <1285824982.5211.675.camel@edumazet-laptop> <1285833189.2615.31.camel@edumazet-laptop> <20100930011417.6ca16ed7.akpm@linux-foundation.org> <1285842136.2615.251.camel@edumazet-laptop> <20100930094558.97c9afa2.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Andrew Morton Return-path: Received: from mail-fx0-f46.google.com ([209.85.161.46]:37381 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753778Ab0I3R24 (ORCPT ); Thu, 30 Sep 2010 13:28:56 -0400 In-Reply-To: <20100930094558.97c9afa2.akpm@linux-foundation.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Le jeudi 30 septembre 2010 =C3=A0 09:45 -0700, Andrew Morton a =C3=A9cr= it : > Could eliminate `p' I guess, but that would involve using > __get_cpu_var() as an lval, which looks vile and might generate worse > code. >=20 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 noinlin= e. > 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) :=20 pretty good ;) c02e5930 : 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 c02e5940: 40 inc %eax c02e5941: 64 a3 44 29 7d c0 mov %eax,%fs:0xc07d2944 c02e5947: c9 leave =20 c02e5948: c3 ret =20 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 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 Signed-off-by: Nick Piggin Signed-off-by: Dave Chinner --- 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, st= ruct inode *inode) } EXPORT_SYMBOL_GPL(inode_add_to_lists); =20 +#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 alloca= tions, + * to renew the exhausted range. + * + * This does not significantly increase overflow rate because every CP= U 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 incr= ease + * 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 =3D __this_cpu_read(last_ino); +#ifdef CONFIG_SMP + if (unlikely((res & (LAST_INO_BATCH - 1)) =3D=3D 0)) { + static atomic_t shared_last_ino; + int next =3D atomic_add_return(LAST_INO_BATCH, &shared_last_ino); + + res =3D 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 counte= r - * here to attempt to avoid that. - */ - static unsigned int last_ino; struct inode *inode; =20 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 =3D ++last_ino; + inode->i_ino =3D last_ino_get(); inode->i_state =3D 0; spin_unlock(&inode_lock); } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html