From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933678AbcA2VVw (ORCPT ); Fri, 29 Jan 2016 16:21:52 -0500 Received: from alln-iport-6.cisco.com ([173.37.142.93]:51238 "EHLO alln-iport-6.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932966AbcA2VVu (ORCPT ); Fri, 29 Jan 2016 16:21:50 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: =?us-ascii?q?A0D7AQAF16tW/4ENJK1egzqKF7E3AQ2BY?= =?us-ascii?q?4YPAoE1OBQBAQEBAQEBgQqEQgEBBDhAARALDgoJFg8JAwIBAgFFBg0IAQGIF8B?= =?us-ascii?q?TAQEBAQEBAQEBAQEBAQEBAQEBGAuGAoQ3iGwBBI4YiFaNS4kfhVKOPR4BAUKED?= =?us-ascii?q?RuJKwEBAQ?= X-IronPort-AV: E=Sophos;i="5.22,366,1449532800"; d="scan'208";a="232865307" Subject: Re: computing drop-able caches To: Johannes Weiner References: <56AAA77D.7090000@cisco.com> <20160128235815.GA5953@cmpxchg.org> <56AABA79.3030103@cisco.com> <56AAC085.9060509@cisco.com> <20160129015534.GA6401@cmpxchg.org> Cc: Alexander Viro , Michal Hocko , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Khalid Mughal (khalidm)" , "xe-kernel@external.cisco.com" , Rik van Riel From: Daniel Walker Message-ID: <56ABD7EB.7000404@cisco.com> Date: Fri, 29 Jan 2016 13:21:47 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <20160129015534.GA6401@cmpxchg.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Auto-Response-Suppress: DR, OOF, AutoReply Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/28/2016 05:55 PM, Johannes Weiner wrote: > On Thu, Jan 28, 2016 at 05:29:41PM -0800, Daniel Walker wrote: >> On 01/28/2016 05:03 PM, Daniel Walker wrote: >> [regarding MemAvaiable] >> >> This new metric purportedly helps usrespace assess available memory. But, >> its again based on heuristic, it takes 1/2 of page cache as reclaimable.. > No, it takes the smaller value of cache/2 and the low watermark, which > is a fraction of memory. Actually, that does look a little weird. Rik? > > We don't age cache without memory pressure, you don't know how much is > used until you start taking some away. Heuristics is all we can offer. With a simple busybox root system I get this, MemTotal: 16273996 kB MemFree: 16137920 kB MemAvailable: 16046132 kB shouldn't MemAvailable be at least the same as MemFree ? I changed the code somewhat so it subtracted the wmark_low only, or the pagecache/2 only, both are still under MemFree. This system has very little drop-able caches. Daniel