From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: Why kmem_cache_free occupy CPU for more than 10 seconds? From: Peter Zijlstra In-Reply-To: References: <84144f020704102353r7dcc3538u2e34237d3496630e@mail.gmail.com> Content-Type: text/plain Date: Wed, 11 Apr 2007 12:38:31 +0200 Message-Id: <1176287911.6893.47.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Zhao Forrest Cc: Pekka Enberg , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wed, 2007-04-11 at 17:53 +0800, Zhao Forrest wrote: > I got some new information: > Before soft lockup message is out, we have: > [root@nsgsh-dhcp-149 home]# cat /proc/slabinfo |grep buffer_head > buffer_head 10927942 10942560 120 32 1 : tunables 32 > 16 8 : slabdata 341955 341955 6 : globalstat 37602996 11589379 > 1174373 6 0 1 6918 12166031 1013708 > : cpustat 35254590 2350698 13610965 907286 > > Then after buffer_head is freed, we have: > [root@nsgsh-dhcp-149 home]# cat /proc/slabinfo |grep buffer_head > buffer_head 9542 36384 120 32 1 : tunables 32 16 > 8 : slabdata 1137 1137 245 : globalstat 37602996 11589379 > 1174373 6 0 1 6983 20507478 > 1708818 : cpustat 35254625 2350704 16027174 1068367 > > Does this huge number of buffer_head cause the soft lockup? __blkdev_put() takes the BKL and bd_mutex invalidate_mapping_pages() tries to take the PageLock But no other looks seem held while free_buffer_head() is called All these locks are preemptible (CONFIG_PREEMPT_BKL?=y) and should not hog the cpu like that, what preemption mode have you got selected? (CONFIG_PREEMPT_VOLUNTARY?=y) Does this fix it? --- fs/buffer.c~ 2007-02-01 12:00:34.000000000 +0100 +++ fs/buffer.c 2007-04-11 12:35:48.000000000 +0200 @@ -3029,6 +3029,8 @@ out: struct buffer_head *next = bh->b_this_page; free_buffer_head(bh); bh = next; + + cond_resched(); } while (bh != buffers_to_free); } return ret; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org