From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 9F23C6B004F for ; Thu, 25 Jun 2009 11:03:19 -0400 (EDT) Received: by gxk3 with SMTP id 3so1675146gxk.14 for ; Thu, 25 Jun 2009 08:03:22 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1245941665.6459.18.camel@lts-notebook> References: <20090625183616.23b55b24.minchan.kim@barrios-desktop> <2f11576a0906250714o5d77db11wd32c1c7139753cb5@mail.gmail.com> <28c262360906250744h5bf9f0a0w265d8c35e7d69335@mail.gmail.com> <1245941665.6459.18.camel@lts-notebook> Date: Fri, 26 Jun 2009 00:03:22 +0900 Message-ID: <28c262360906250803p31e72a2at73ff1af823615260@mail.gmail.com> Subject: Re: [PATCH] prevent to reclaim anon page of lumpy reclaim for no swap space From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Lee Schermerhorn Cc: KOSAKI Motohiro , Andrew Morton , Rik van Riel , KAMEZAWA Hiroyuki , linux-mm , lkml List-ID: Hi, Lee. On Thu, Jun 25, 2009 at 11:54 PM, Lee Schermerhorn wrote: > On Thu, 2009-06-25 at 23:44 +0900, Minchan Kim wrote: >> On Thu, Jun 25, 2009 at 11:14 PM, KOSAKI >> Motohiro wrote: >> >> This patch prevent to reclaim anon page in case of no swap space. >> >> VM already prevent to reclaim anon page in various place. >> >> But it doesnt't prevent it for lumpy reclaim. >> >> >> >> It shuffles lru list unnecessary so that it is pointless. >> > >> > NAK. >> > >> > 1. if system have no swap, add_to_swap() never get swap entry. >> > =C2=A0 eary check don't improve performance so much. >> >> Hmm. I mean no swap space but not no swap device. >> add_to_swap ? You mean Rik pointed me out ? >> If system have swap device, Rik's pointing is right. >> I will update his suggestion. >> >> > 2. __isolate_lru_page() is not only called lumpy reclaim case, but >> > also be called >> > =C2=A0 =C2=A0normal reclaim. >> >> You mean about performance degradation ? >> I think most case have enough swap space and then one condition >> variable(nr_swap_page) check is trivial. I think. >> We can also use [un]likely but I am not sure it help us. >> >> >> > 3. if system have no swap, anon pages shuffuling doesn't cause any mat= ter. >> >> Again, I mean no swap space but no swap device system. >> And I have a plan to remove anon_vma in no swap device system. >> >> As you point me out, it's pointless in no swap device system. >> I don't like unnecessary structure memory footprint and locking overhead= . >> I think no swap device system is problem in server environment as well >> as embedded. but I am not sure when I will do. :) >> > > How will we walk the reverse map for try_to_unmap() for page migration > or try_to_munlock() w/o anon_vma? =C2=A0Perhaps one can remove anon_vma w= hen > there is no swap device and migration and the unevictable lru are not > configured--e.g., for embedded systems. You're right. In addition, there are HWPoison and maybe KSM. Also, unevictable lru list isn't option any more even embedded system. Actually I considered it in embedded system as you said. I think above enumerated cases are not needed in embedded system. Memory footprint and unnecessary locking is more important in embedded since small memory and realtime. Anyway, I think it's not easy so now it's just plan. Welcome to any comment to prevent my vain effort. :) Thanks for valuable comment. Lee. :) > Lee > > --=20 Kinds regards, Minchan Kim -- 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/ . Don't email: email@kvack.org