Matthew Ahrens 8fbf432ae2 anon_pages are not free/evictable
`arc_free_memory()` returns the amount of memory that the ARC considers
to be free.  This includes pages that are not actually free, but can be
evicted with essentially zero cost (without doing any i/o), for example
the page cache.  The ARC can "squeeze out" any pages included in this
calculation, leaving only `arc_sys_free` (1/64th of RAM) for these
free/evictable pages.

Included in the count of free/evictable pages is
`nr_inactive_anon_pages()`, which is described as "Anonymous memory that
has not been used recently and can be swapped out".  These pages would
have to be written out to disk (swap) in order to evict them, and they
are not included in `/proc/meminfo`'s `MemAvailable`.

Therefore it is not appropriate for `nr_inactive_anon_pages()` to be
included in the free/evictable memory returned by `arc_free_memory()`,
because the ARC shouldn't (intentionally) make the system swap.

This commit removes `nr_inactive_anon_pages()` from the memory returned
by `arc_free_memory()`.  This is a step towards enabling the ARC to
manage free memory by monitoring it and reducing the ARC size as we
notice that there is insufficient free memory (in the `arc_reap_zthr`),
rather than the current method of relying on the `arc_shrinker`
callback.

Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: George Wilson <gwilson@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #10575
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.

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Official Resources

Installation

Full documentation for installing OpenZFS on your favorite Linux distribution can be found at the ZoL Site.

Contribute & Develop

We have a separate document with contribution guidelines.

We have a Code of Conduct.

Release

OpenZFS is released under a CDDL license. For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197

Supported Kernels

  • The META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are 12-STABLE and 13-CURRENT.
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