svn commit: r351673 - in head: lib/libmemstat share/man/man9 sys/cddl/compat/opensolaris/kern sys/kern sys/vm

[Slawa Olhovchenkov]

On Tue, Sep 03, 2019 at 10:02:59AM +0300, Andriy Gapon wrote:

> On 02/09/2019 01:22, Mark Johnston wrote:
> > Author: markj
> > Date: Sun Sep  1 22:22:43 2019
> > New Revision: 351673
> > URL: https://svnweb.freebsd.org/changeset/base/351673
> > 
> > Log:
> >   Extend uma_reclaim() to permit different reclamation targets.
> >   
> >   The page daemon periodically invokes uma_reclaim() to reclaim cached
> >   items from each zone when the system is under memory pressure.  This
> >   is important since the size of these caches is unbounded by default.
> >   However it also results in bursts of high latency when allocating from
> >   heavily used zones as threads miss in the per-CPU caches and must
> >   access the keg in order to allocate new items.
> >   
> >   With r340405 we maintain an estimate of each zone's usage of its
> >   (per-NUMA domain) cache of full buckets.  Start making use of this
> >   estimate to avoid reclaiming the entire cache when under memory
> >   pressure.  In particular, introduce TRIM, DRAIN and DRAIN_CPU
> >   verbs for uma_reclaim() and uma_zone_reclaim().  When trimming, only
> >   items in excess of the estimate are reclaimed.  Draining a zone
> >   reclaims all of the cached full buckets (the previous behaviour of
> >   uma_reclaim()), and may further drain the per-CPU caches in extreme
> >   cases.
> >   
> >   Now, when under memory pressure, the page daemon will trim zones
> >   rather than draining them.  As a result, heavily used zones do not incur
> >   bursts of bucket cache misses following reclamation, but large, unused
> >   caches will be reclaimed as before.
> 
> Mark,
> 
> have you considered running UMA_RECLAIM_TRIM periodically, even without a memory
> pressure?
> I think that with such a periodic trimming there will be less need to invoke
> vm_lowmem().
> 
> Also, I think that we would be able to retire (or re-purpose) lowmem_period.
> E.g., the trimming would be done every lowmem_period, but vm_lowmem() would not
> be throttled.
> 
> One example of the throttling of vm_lowmem being bad is its interaction with the
> ZFS ARC.  When there is a spike in memory usage we want the ARC to adapt as
> quickly as possible.  But at present the lowmem_period logic interferes with that.

Some time ago, I sent Mark a patch that implements this logic,
specialy for ARC and mbuf cooperate. Mostly problem I am see at this
work -- very slowly vm_page_free(). May be currenly this is more
speedy...