From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id AB8986B002E for ; Mon, 17 Oct 2011 16:14:43 -0400 (EDT) MIME-Version: 1.0 Message-ID: <7f94da39-4855-46b6-96d3-ab5ddbaed039@default> Date: Mon, 17 Oct 2011 13:14:23 -0700 (PDT) From: Dan Magenheimer Subject: RE: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock References: <1318448460-5930-1-git-send-email-sjenning@linux.vnet.ibm.com 3e84809b-a45d-4980-b342-c2d671f87f79@default> In-Reply-To: <3e84809b-a45d-4980-b342-c2d671f87f79@default> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Dan Magenheimer , 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 > From: Dan Magenheimer > Sent: Wednesday, October 12, 2011 2:39 PM > 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; brkin= g@linux.vnet.ibm.com > Subject: RE: [PATCH] staging: zcache: remove zcache_direct_reclaim_lock >=20 > > 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(). >=20 > Yes, this looks to be leftover code from early in kztmem/zcache > development. Good analysis. >=20 > > 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() >=20 > Might it be worthwhile to add a BUG/ASSERT for the presence > of PF_MEMALLOC, or at least a comment in the code? >=20 > > 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 >=20 > With added code/comment per above... > Acked-by: Dan Magenheimer After Seth's further analysis, ignore my conditional and consider v1 of this patch: Acked-by: Dan Magenheimer -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org