From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx134.postini.com [74.125.245.134]) by kanga.kvack.org (Postfix) with SMTP id 0324F6B004A for ; Wed, 7 Mar 2012 12:19:10 -0500 (EST) Message-ID: <4F5798B1.5070005@jp.fujitsu.com> Date: Wed, 07 Mar 2012 12:19:45 -0500 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [RFC][PATCH] avoid swapping out with swappiness==0 References: <65795E11DBF1E645A09CEC7EAEE94B9CB9455FE2@USINDEVS02.corp.hds.com> <20120305215602.GA1693@redhat.com> In-Reply-To: <20120305215602.GA1693@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: jweiner@redhat.com Cc: satoru.moriya@hds.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, riel@redhat.com, lwoodman@redhat.com, shaohua.li@intel.com, kosaki.motohiro@jp.fujitsu.com, dle-develop@lists.sourceforge.net, seiji.aguchi@hds.com On 3/5/2012 4:56 PM, Johannes Weiner wrote: > On Fri, Mar 02, 2012 at 12:36:40PM -0500, Satoru Moriya wrote: >> Sometimes we'd like to avoid swapping out anonymous memory >> in particular, avoid swapping out pages of important process or >> process groups while there is a reasonable amount of pagecache >> on RAM so that we can satisfy our customers' requirements. >> >> OTOH, we can control how aggressive the kernel will swap memory pages >> with /proc/sys/vm/swappiness for global and >> /sys/fs/cgroup/memory/memory.swappiness for each memcg. >> >> But with current reclaim implementation, the kernel may swap out >> even if we set swappiness==0 and there is pagecache on RAM. >> >> This patch changes the behavior with swappiness==0. If we set >> swappiness==0, the kernel does not swap out completely >> (for global reclaim until the amount of free pages and filebacked >> pages in a zone has been reduced to something very very small >> (nr_free + nr_filebacked < high watermark)). >> >> Any comments are welcome. > > Last time I tried that (getting rid of sc->may_swap, using > !swappiness), it was rejected it as there were users who relied on > swapping very slowly with this setting. > > KOSAKI-san, do I remember correctly? Do you still think it's an > issue? > > Personally, I still think it's illogical that !swappiness allows > swapping and would love to see this patch go in. Thank you. I brought back to memory it. Unfortunately DB folks are still mainly using RHEL5 generation distros. At that time, swapiness=0 doesn't mean disabling swap. They want, "don't swap as far as kernel has any file cache page". but linux don't have such feature. then they used swappiness for emulate it. So, I think this patch clearly make userland harm. Because of, we don't have an alternative way. -- 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