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Re: computing drop-able caches

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On Thu, Jan 28, 2016 at 03:42:53PM -0800, Daniel Walker wrote:
> "Currently there is no way to figure out the droppable pagecache size
> from the meminfo output. The MemFree size can shrink during normal
> system operation, when some of the memory pages get cached and is
> reflected in "Cached" field. Similarly for file operations some of
> the buffer memory gets cached and it is reflected in "Buffers" field.
> The kernel automatically reclaims all this cached & buffered memory,
> when it is needed elsewhere on the system. The only way to manually
> reclaim this memory is by writing 1 to /proc/sys/vm/drop_caches. "

[...]

> The point of the whole exercise is to get a better idea of free memory for
> our employer. Does it make sense to do this for computing free memory?

/proc/meminfo::MemAvailable was added for this purpose. See the doc
text in Documentation/filesystem/proc.txt.

It's an approximation, however, because this question is not easy to
answer. Pages might be in various states and uses that can make them
unreclaimable.

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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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