From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx193.postini.com [74.125.245.193]) by kanga.kvack.org (Postfix) with SMTP id 530D96B00F1 for ; Wed, 4 Apr 2012 13:38:20 -0400 (EDT) Received: by pbcup15 with SMTP id up15so625599pbc.14 for ; Wed, 04 Apr 2012 10:38:19 -0700 (PDT) Message-ID: <4F7C870B.6020807@gmail.com> Date: Wed, 04 Apr 2012 10:38:19 -0700 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> <4F5798B1.5070005@jp.fujitsu.com> <65795E11DBF1E645A09CEC7EAEE94B9CB951A45F@USINDEVS02.corp.hds.com> <65795E11DBF1E645A09CEC7EAEE94B9C01454D13A6@USINDEVS02.corp.hds.com> <4F7ADE1A.2050004@redhat.com> In-Reply-To: <4F7ADE1A.2050004@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Marchand Cc: KOSAKI Motohiro , Satoru Moriya , "jweiner@redhat.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "riel@redhat.com" , "lwoodman@redhat.com" , "shaohua.li@intel.com" , "dle-develop@lists.sourceforge.net" , Seiji Aguchi , kosaki.motohiro@gmail.com (4/3/12 4:25 AM), Jerome Marchand wrote: > On 04/02/2012 07:10 PM, KOSAKI Motohiro wrote: >> 2012/3/30 Satoru Moriya: >>> Hello Kosaki-san, >>> >>> On 03/07/2012 01:18 PM, Satoru Moriya wrote: >>>> On 03/07/2012 12:19 PM, KOSAKI Motohiro wrote: >>>>> 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. >>> >>> As I wrote in the previous mail(see below), with this patch >>> the kernel begins to swap out when the sum of free pages and >>> filebacked pages reduces less than watermark_high. > > Actually, this is true only for global reclaims. Reclaims in cgroup can fail > in this case. > >>> >>> So the kernel reclaims pages like following. >>> >>> nr_free + nr_filebacked>= watermark_high: reclaim only filebacked pages >>> nr_free + nr_filebacked< watermark_high: reclaim only anonymous pages >> >> How? > > get_scan_count() checks that case explicitly: > > if (global_reclaim(sc)) { > free = zone_page_state(mz->zone, NR_FREE_PAGES); > /* If we have very few page cache pages, > force-scan anon pages. */ > if (unlikely(file + free<= high_wmark_pages(mz->zone))) { > fraction[0] = 1; > fraction[1] = 0; > denominator = 1; > goto out; > } > } Eek. This is silly. Nowaday many people enabled THP and it increase zone watermark. so, high watermask is not good threshold anymore. -- 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