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Re: computing drop-able caches

From Daniel Walker <danielwa@cisco.com>
Newsgroups linux.kernel
Subject Re: computing drop-able caches
Date 2016-01-29 22:30 +0100
Message-ID <qWoMb-IK-19@gated-at.bofh.it> (permalink)
References <qW4u6-2pQ-9@gated-at.bofh.it> <qW4DN-2tl-19@gated-at.bofh.it> <qW5Jv-3s7-11@gated-at.bofh.it> <qW6vW-3Ny-47@gated-at.bofh.it> <qW6vW-3Ny-45@gated-at.bofh.it>
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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

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Thread

computing drop-able caches Daniel Walker <danielwa@cisco.com> - 2016-01-29 00:50 +0100
  Re: computing drop-able caches Johannes Weiner <hannes@cmpxchg.org> - 2016-01-29 01:00 +0100
    Re: computing drop-able caches Daniel Walker <danielwa@cisco.com> - 2016-01-29 02:10 +0100
      Re: computing drop-able caches Johannes Weiner <hannes@cmpxchg.org> - 2016-01-29 03:00 +0100
        Re: computing drop-able caches Daniel Walker <danielwa@cisco.com> - 2016-01-29 22:30 +0100
          Re: computing drop-able caches Johannes Weiner <hannes@cmpxchg.org> - 2016-01-29 23:40 +0100
        Re: computing drop-able caches Rik van Riel <riel@redhat.com> - 2016-01-29 23:50 +0100
          Re: computing drop-able caches "Khalid Mughal (khalidm)" <khalidm@cisco.com> - 2016-02-08 22:10 +0100

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