Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751465Ab0HSBmy (ORCPT ); Wed, 18 Aug 2010 21:42:54 -0400 Received: from mga03.intel.com ([143.182.124.21]:64740 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751086Ab0HSBmw (ORCPT ); Wed, 18 Aug 2010 21:42:52 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.56,230,1280732400"; d="scan'208";a="314300183" Date: Thu, 19 Aug 2010 09:42:49 +0800 From: Shaohua Li To: "Wu, Fengguang" Cc: Johannes Weiner , Matthew Wilcox , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [TESTCASE] Clean pages clogging the VM Message-ID: <20100819014249.GA22092@sli10-desk.sh.intel.com> References: <20100809133000.GB6981@wil.cx> <20100817195001.GA18817@linux.intel.com> <20100818141308.GD1779@cmpxchg.org> <20100818160613.GE9431@localhost> <20100818160731.GA15002@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100818160731.GA15002@localhost> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5020 Lines: 125 On Thu, Aug 19, 2010 at 12:07:31AM +0800, Wu, Fengguang wrote: > On Thu, Aug 19, 2010 at 12:06:13AM +0800, Wu Fengguang wrote: > > On Wed, Aug 18, 2010 at 04:13:08PM +0200, Johannes Weiner wrote: > > > Hi Matthew, > > > > > > On Tue, Aug 17, 2010 at 03:50:01PM -0400, Matthew Wilcox wrote: > > > > > > > > No comment on this? Was it just that I posted it during the VM summit? > > > > > > I have not forgotten about it. I just have a hard time reproducing > > > those extreme stalls you observed. > > > > > > Running that test on a 2.5GHz machine with 2G of memory gives me > > > stalls of up to half a second. The patchset I am experimenting with > > > gets me down to peaks of 70ms, but it needs further work. > > > > > > Mapped file pages get two rounds on the LRU list, so once the VM > > > starts scanning, it has to go through all of them twice and can only > > > reclaim them on the second encounter. > > > > > > At that point, since we scan without making progress, we start waiting > > > for IO, which is not happening in this case, so we sit there until a > > > timeout expires. > > > > Right, this could lead to some 1s stall. Shaohua and me also noticed > > this when investigating the responsiveness issues. And we are wondering > > if it makes sense to do congestion_wait() only when the bdi is really > > congested? There are no IO underway anyway in this case. > > > > > This stupid-waiting can be improved, and I am working on that. But > > > > Yeah, stupid waiting :) How about this one? Subject: mm: check device is really congested before sleep in direct page reclaim congestion_wait() blindly sleep without checking if device is really congested. In a workload without any write, it can cause direct page reclaim sleep 100ms and hasn't any help for page reclaim. There might be other places calling congestion_wait() and need check if device is really congested, but I can't audit all, so this just changes the direct page reclaim code path. The new congestion_wait_check() will make sure at least one device is congested before going into sleep. Signed-off-by: Shaohua Li --- include/linux/backing-dev.h | 1 + mm/backing-dev.c | 14 ++++++++++++-- mm/vmscan.c | 2 +- 3 files changed, 14 insertions(+), 3 deletions(-) Index: linux/mm/backing-dev.c =================================================================== --- linux.orig/mm/backing-dev.c 2010-08-18 16:41:04.000000000 +0800 +++ linux/mm/backing-dev.c 2010-08-19 08:59:14.000000000 +0800 @@ -725,13 +725,16 @@ static wait_queue_head_t congestion_wqh[ __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1]) }; +static atomic_t nr_congested_bdi[2]; + void clear_bdi_congested(struct backing_dev_info *bdi, int sync) { enum bdi_state bit; wait_queue_head_t *wqh = &congestion_wqh[sync]; bit = sync ? BDI_sync_congested : BDI_async_congested; - clear_bit(bit, &bdi->state); + if (test_and_clear_bit(bit, &bdi->state)) + atomic_dec(&nr_congested_bdi[sync]); smp_mb__after_clear_bit(); if (waitqueue_active(wqh)) wake_up(wqh); @@ -743,7 +746,8 @@ void set_bdi_congested(struct backing_de enum bdi_state bit; bit = sync ? BDI_sync_congested : BDI_async_congested; - set_bit(bit, &bdi->state); + if (!test_and_set_bit(bit, &bdi->state)) + atomic_inc(&nr_congested_bdi[sync]); } EXPORT_SYMBOL(set_bdi_congested); @@ -769,3 +773,9 @@ long congestion_wait(int sync, long time } EXPORT_SYMBOL(congestion_wait); +long congestion_wait_check(int sync, long timeout) +{ + if (atomic_read(&nr_congested_bdi[sync]) == 0) + return 0; + return congestion_wait(sync, timeout); +} Index: linux/include/linux/backing-dev.h =================================================================== --- linux.orig/include/linux/backing-dev.h 2010-08-18 16:41:04.000000000 +0800 +++ linux/include/linux/backing-dev.h 2010-08-18 16:41:23.000000000 +0800 @@ -285,6 +285,7 @@ enum { void clear_bdi_congested(struct backing_dev_info *bdi, int sync); void set_bdi_congested(struct backing_dev_info *bdi, int sync); long congestion_wait(int sync, long timeout); +long congestion_wait_check(int sync, long timeout); static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi) Index: linux/mm/vmscan.c =================================================================== --- linux.orig/mm/vmscan.c 2010-08-18 16:41:04.000000000 +0800 +++ linux/mm/vmscan.c 2010-08-18 16:41:23.000000000 +0800 @@ -1910,7 +1910,7 @@ static unsigned long do_try_to_free_page /* Take a nap, wait for some writeback to complete */ if (!sc->hibernation_mode && sc->nr_scanned && priority < DEF_PRIORITY - 2) - congestion_wait(BLK_RW_ASYNC, HZ/10); + congestion_wait_check(BLK_RW_ASYNC, HZ/10); } out: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/