From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 29 Jan 2016 17:33:46 -0500 From: Johannes Weiner To: Daniel Walker 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 Subject: Re: computing drop-able caches Message-ID: <20160129223346.GA30068@cmpxchg.org> References: <56AAA77D.7090000@cisco.com> <20160128235815.GA5953@cmpxchg.org> <56AABA79.3030103@cisco.com> <56AAC085.9060509@cisco.com> <20160129015534.GA6401@cmpxchg.org> <56ABD7EB.7000404@cisco.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56ABD7EB.7000404@cisco.com> Sender: owner-linux-mm@kvack.org List-ID: On Fri, Jan 29, 2016 at 01:21:47PM -0800, Daniel Walker wrote: > 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. No, a portion of memory is reserved for the kernel and not available to userland. If the kernel doesn't use it it will remain free. Hence the lower MemAvailable. -- 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