From: Johannes Weiner <hannes@cmpxchg.org>
To: Daniel Walker <danielwa@cisco.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, "Khalid Mughal (khalidm)" <khalidm@cisco.com>,
"xe-kernel@external.cisco.com" <xe-kernel@external.cisco.com>
Subject: Re: computing drop-able caches
Date: Thu, 28 Jan 2016 18:58:15 -0500 [thread overview]
Message-ID: <20160128235815.GA5953@cmpxchg.org> (raw)
In-Reply-To: <56AAA77D.7090000@cisco.com>
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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WARNING: multiple messages have this Message-ID (diff)
From: Johannes Weiner <hannes@cmpxchg.org>
To: Daniel Walker <danielwa@cisco.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, "Khalid Mughal (khalidm)" <khalidm@cisco.com>,
"xe-kernel@external.cisco.com" <xe-kernel@external.cisco.com>
Subject: Re: computing drop-able caches
Date: Thu, 28 Jan 2016 18:58:15 -0500 [thread overview]
Message-ID: <20160128235815.GA5953@cmpxchg.org> (raw)
In-Reply-To: <56AAA77D.7090000@cisco.com>
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.
next prev parent reply other threads:[~2016-01-28 23:58 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-28 23:42 computing drop-able caches Daniel Walker
2016-01-28 23:42 ` Daniel Walker
2016-01-28 23:58 ` Johannes Weiner [this message]
2016-01-28 23:58 ` Johannes Weiner
2016-01-29 1:03 ` Daniel Walker
2016-01-29 1:03 ` Daniel Walker
2016-01-29 1:29 ` Daniel Walker
2016-01-29 1:55 ` Johannes Weiner
2016-01-29 1:55 ` Johannes Weiner
2016-01-29 21:21 ` Daniel Walker
2016-01-29 21:21 ` Daniel Walker
2016-01-29 22:33 ` Johannes Weiner
2016-01-29 22:33 ` Johannes Weiner
2016-01-29 22:41 ` Rik van Riel
2016-01-29 22:41 ` Rik van Riel
2016-02-08 20:57 ` Khalid Mughal (khalidm)
2016-02-08 20:57 ` Khalid Mughal (khalidm)
2016-02-10 18:04 ` Daniel Walker
2016-02-10 18:04 ` Daniel Walker
2016-02-10 18:13 ` Dave Hansen
2016-02-10 18:13 ` Dave Hansen
2016-02-10 19:11 ` Daniel Walker
2016-02-10 19:11 ` Daniel Walker
2016-02-11 22:11 ` Rik van Riel
2016-02-12 18:01 ` Khalid Mughal (khalidm)
2016-02-12 21:46 ` Dave Hansen
2016-02-12 21:46 ` Dave Hansen
2016-02-12 21:46 ` Dave Hansen
2016-02-12 22:15 ` Johannes Weiner
2016-02-12 22:15 ` Johannes Weiner
2016-02-12 22:15 ` Johannes Weiner
2016-02-12 18:06 ` Dave Hansen
2016-02-12 18:06 ` Dave Hansen
2016-02-12 18:15 ` Daniel Walker
2016-02-12 18:15 ` Daniel Walker
2016-02-12 18:18 ` Dave Hansen
2016-02-12 18:18 ` Dave Hansen
2016-02-12 18:25 ` Daniel Walker
2016-02-12 18:25 ` Daniel Walker
2016-02-12 20:15 ` Daniel Walker
2016-02-12 20:15 ` Daniel Walker
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