From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754092Ab1JLUl0 (ORCPT ); Wed, 12 Oct 2011 16:41:26 -0400 Received: from rcsinet15.oracle.com ([148.87.113.117]:57182 "EHLO rcsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171Ab1JLUlZ convert rfc822-to-8bit (ORCPT ); Wed, 12 Oct 2011 16:41:25 -0400 MIME-Version: 1.0 Message-ID: <3e84809b-a45d-4980-b342-c2d671f87f79@default> Date: Wed, 12 Oct 2011 13:39:10 -0700 (PDT) From: Dan Magenheimer To: Seth Jennings , gregkh@suse.de Cc: cascardo@holoscopio.com, rdunlap@xenotime.net, devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcj@linux.vnet.ibm.com, brking@linux.vnet.ibm.com Subject: RE: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock References: <1318448460-5930-1-git-send-email-sjenning@linux.vnet.ibm.com> In-Reply-To: <1318448460-5930-1-git-send-email-sjenning@linux.vnet.ibm.com> X-Priority: 3 X-Mailer: Oracle Beehive Extensions for Outlook 2.0.1.4.1.0 (410211) [OL 12.0.6562.5003] Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT X-Source-IP: acsinet21.oracle.com [141.146.126.237] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090208.4E95FAFB.00CF:SCFMA922111,ss=1,re=-4.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Seth Jennings [mailto:sjenning@linux.vnet.ibm.com] > Subject: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock > > zcache_do_preload() currently does a spin_trylock() on the > zcache_direct_reclaim_lock. Holding this lock intends to prevent > shrink_zcache_memory() from evicting zbud pages as a result > of a preload. > > However, it also prevents two threads from > executing zcache_do_preload() at the same time. The first > thread will obtain the lock and the second thread's spin_trylock() > will fail (an aborted preload) causing the page to be either lost > (cleancache) or pushed out to the swap device (frontswap). It > also doesn't ensure that the call to shrink_zcache_memory() is > on the same thread as the call to zcache_do_preload(). Yes, this looks to be leftover code from early in kztmem/zcache development. Good analysis. > Additional, there is no need for this mechanism because all > zcache_do_preload() calls that come down from cleancache already > have PF_MEMALLOC set in the process flags which prevents > direct reclaim in the memory manager. If the zcache_do_preload() Might it be worthwhile to add a BUG/ASSERT for the presence of PF_MEMALLOC, or at least a comment in the code? > call is done from the frontswap path, we _want_ reclaim to be > done (which it isn't right now). > > This patch removes the zcache_direct_reclaim_lock and related > statistics in zcache. > > Based on v3.1-rc8 > > Signed-off-by: Seth Jennings > Reviewed-by: Dave Hansen With added code/comment per above... Acked-by: Dan Magenheimer