Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936065Ab3DPUA0 (ORCPT ); Tue, 16 Apr 2013 16:00:26 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:46126 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935189Ab3DPUAY (ORCPT ); Tue, 16 Apr 2013 16:00:24 -0400 Date: Tue, 16 Apr 2013 13:00:21 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Oskar Andero cc: Dan Carpenter , Greg Kroah-Hartman , "devel@driverdev.osuosl.org" , Brian Swetland , "linux-kernel@vger.kernel.org" , "Dolkow, Snild" , "Lekanovic, Radovan" Subject: Re: [PATCH] lowmemorykiller: prevent multiple instances of low memory killer In-Reply-To: <20130416105950.GB22161@caracas.corpusers.net> Message-ID: References: <1366031009-21958-1-git-send-email-oskar.andero@sonymobile.com> <20130415131815.GG6638@mwanda> <20130415141358.GO6692@mwanda> <20130415150356.GA22161@caracas.corpusers.net> <20130415194947.GA26557@kroah.com> <20130416061904.GH6638@mwanda> <20130416105950.GB22161@caracas.corpusers.net> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2163 Lines: 50 On Tue, 16 Apr 2013, Oskar Andero wrote: > > > The comment in shrinker.h is misleading, not the source code. > > > do_shrinker_shrink() will fail for anything negative and 0. > > > > The comment is correct. The only acceptable negative return is -1. > > Look at the second time do_shrinker_shrink() is called from > > shrink_slab(). > > > > 283 while (total_scan >= batch_size) { > > 284 int nr_before; > > 285 > > 286 nr_before = do_shrinker_shrink(shrinker, shrink, 0); > > 287 shrink_ret = do_shrinker_shrink(shrinker, shrink, > > 288 batch_size); > > 289 if (shrink_ret == -1) > > 290 break; > > 291 if (shrink_ret < nr_before) > > 292 ret += nr_before - shrink_ret; > > 293 count_vm_events(SLABS_SCANNED, batch_size); > > Yes, the comment is correct with what is implemented in the code, but > that doesn't mean the code is right. IMHO, relaying on magical numbers is highly > questionable coding style. > No, it's not. This is controlled higher in shrink_slab() by this: max_pass = do_shrinker_shrink(shrinker, shrink, 0); if (max_pass <= 0) continue; and your patch is implemented incorrectly, i.e. it does not return LMK_BUSY if the spinlock is contended which needlessly recalls the shrinker later. You have a couple of options: - return -1 when the spinlock is contended immediately when !sc->nr_to_scan (although it should really be a cmpxchg since a spinlock isn't needed), or - protect the for_each_process() loop in lowmem_shrink() with an actual spinlock that will detect any previously killed process since it will have the TIF_MEMDIE bit set. -- 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/