From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id C61886B003D for ; Sun, 13 Dec 2009 23:29:52 -0500 (EST) Message-ID: <4B25BF39.5020401@redhat.com> Date: Sun, 13 Dec 2009 23:29:45 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH v2] vmscan: limit concurrent reclaimers in shrink_zone References: <20091211164651.036f5340@annuminas.surriel.com> <28c262360912131614h62d8e0f7qf6ea9ab882f446d4@mail.gmail.com> <4B25BA6E.5010002@redhat.com> <28c262360912132019u7c0b8efpf89b11a6cbe512b3@mail.gmail.com> In-Reply-To: <28c262360912132019u7c0b8efpf89b11a6cbe512b3@mail.gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: lwoodman@redhat.com, akpm@linux-foundation.org, KOSAKI Motohiro , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On 12/13/2009 11:19 PM, Minchan Kim wrote: > On Mon, Dec 14, 2009 at 1:09 PM, Rik van Riel wrote: >> A simpler solution may be to use sleep_on_interruptible, and >> simply have the process continue into shrink_zone() if it >> gets a signal. > > I thought it but I was not sure. > Okay. If it is possible, It' more simple. > Could you repost patch with that? Sure, not a problem. > +The default value is 8. > + > +============================================================= > > > I like this. but why do you select default value as constant 8? > Do you have any reason? > > I think it would be better to select the number proportional to NR_CPU. > ex) NR_CPU * 2 or something. > > Otherwise looks good to me. > > > Pessimistically, I assume that the pageout code spends maybe > 10% of its time on locking (we have seen far, far worse than > this with thousands of processes in the pageout code). That > means if we have more than 10 threads in the pageout code, > we could end up spending more time on locking and less doing > real work - slowing everybody down. > > I rounded it down to the closest power of 2 to come up with > an arbitrary number that looked safe :) > === > > We discussed above. > I want to add your desciption into changelog. The thing is, I don't know if 8 is the best value for the default, which is a reason I made it tunable in the first place. There are a lot of assumptions in my reasoning, and they may be wrong. I suspect that documenting something wrong is probably worse than letting people wonder out the default (and maybe finding a better one). -- All rights reversed. -- 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