From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753921Ab1HVVaT (ORCPT ); Mon, 22 Aug 2011 17:30:19 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:38791 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753744Ab1HVVaQ (ORCPT ); Mon, 22 Aug 2011 17:30:16 -0400 Date: Mon, 22 Aug 2011 14:30:06 -0700 From: Andrew Morton To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dave Chinner Subject: Re: [PATCH 1/2] vmscan: fix initial shrinker size handling Message-Id: <20110822143006.60f4b560.akpm@linux-foundation.org> In-Reply-To: <20110822101721.19462.63082.stgit@zurg> References: <20110822101721.19462.63082.stgit@zurg> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Aug 2011 14:17:21 +0300 Konstantin Khlebnikov wrote: > Shrinker function can returns -1, it means it cannot do anything without a risk of deadlock. > For example prune_super() do this if it cannot grab superblock refrence, even if nr_to_scan=0. > Currenly we interpret this like ULONG_MAX size shrinker, evaluate total_scan according this, > and next time this shrinker can get really big pressure. Let's skip such shrinkers instead. Yes, that looks like a significant oversight. > Also make total_scan signed, otherwise check (total_scan < 0) below never works. Hopefully a smaller oversight. > --- > mm/vmscan.c | 9 ++++++--- > 1 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 29b3612..f174561 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -248,14 +248,18 @@ unsigned long shrink_slab(struct shrink_control *shrink, > > list_for_each_entry(shrinker, &shrinker_list, list) { > unsigned long long delta; > - unsigned long total_scan; > - unsigned long max_pass; > + long total_scan; > + long max_pass; > int shrink_ret = 0; > long nr; > long new_nr; > long batch_size = shrinker->batch ? shrinker->batch > : SHRINK_BATCH; > > + max_pass = do_shrinker_shrink(shrinker, shrink, 0); > + if (max_pass <= 0) > + continue; > + > /* > * copy the current shrinker scan count into a local variable > * and zero it so that other concurrent shrinker invocations > @@ -266,7 +270,6 @@ unsigned long shrink_slab(struct shrink_control *shrink, > } while (cmpxchg(&shrinker->nr, nr, 0) != nr); > > total_scan = nr; > - max_pass = do_shrinker_shrink(shrinker, shrink, 0); > delta = (4 * nr_pages_scanned) / shrinker->seeks; > delta *= max_pass; > do_div(delta, lru_pages + 1); Why was the shrinker call moved to before the alteration of shrinker->nr?