svn commit: r326619 - stable/11/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Peter Jeremy]

On 2017-Dec-06 10:01:02 +0000, Baptiste Daroussin <bapt at FreeBSD.org> wrote:
>Author: bapt
>Date: Wed Dec  6 10:01:02 2017
>New Revision: 326619
>URL: https://svnweb.freebsd.org/changeset/base/326619
>
>Log:
>  MFC r325851:
>  
>  remove the poor emulation of the IllumOS needfree global variable to prevent
>  the ARC reclaim thread running longer than needed.
>  

This change appears to break the backpressure mechanism that forces
ARC to release wired memory.  Running FreeBSD/amd64 r326743, I found
that my system was thrashing badly with almost all memory (~31GB out
of 32GB) wired (including 19GB ARC, 7GB VBox guests).  Running a tool
that just allocates and dirties a large amount of memory had no effect
on the ARC size.  Reverting this change only restores normal behaviour
where ARC will shrink under pressure.

My ZFS boot tunables are:
vfs.zfs.arc_max="24G"
vfs.zfs.arc_meta_limit="12G"

-- 
Peter Jeremy
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