From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753244Ab0I3KWX (ORCPT ); Thu, 30 Sep 2010 06:22:23 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:57150 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751117Ab0I3KWV (ORCPT ); Thu, 30 Sep 2010 06:22:21 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=fBoxr7Pr7Yli9KKnJ68U8cCnfNczDj8EcdDUiylrKT4Lq9wQCZFUShdWhOxGyhtbDV Q9uI6hcMLPPEe9Nz5tynizekvWrL+/WxlOdJLnLIOTnUx9PFymAHXhekK6UmiZ5eej/M 9SkC/DQyCEIAUYKi0GzjkpeMzczOfQdc7IeiI= Subject: [PATCH] fs: inode per-cpu last_ino allocator From: Eric Dumazet To: Andrew Morton Cc: Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20100930011417.6ca16ed7.akpm@linux-foundation.org> 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> Content-Type: text/plain; charset="UTF-8" Date: Thu, 30 Sep 2010 12:22:16 +0200 Message-ID: <1285842136.2615.251.camel@edumazet-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le jeudi 30 septembre 2010 à 01:14 -0700, Andrew Morton a écrit : > Perhaps > > WARN_ON_ONCE(preemptible()); > > if we had a developer-only version of WARN_ON_ONCE, which we don't. Or just use a regular PER_CPU variable, even on !SMP, and get preempt safe implementation. What do you think of following patch, on top of current linux-2.6 tree ? 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 | 45 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 38 insertions(+), 7 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 8646433..122914e 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -624,6 +624,43 @@ 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 noinline unsigned int last_ino_get(void) +{ + unsigned int *p = &get_cpu_var(last_ino); + unsigned int res = *p; + +#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 + *p = ++res; + put_cpu_var(last_ino); + return res; +} + /** * new_inode - obtain an inode * @sb: superblock @@ -638,12 +675,6 @@ 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 +683,7 @@ 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); }