ZFS ARC under memory pressure

[Slawa Olhovchenkov]

On Wed, Aug 17, 2016 at 09:18:20AM +0200, Matthias Gamsjager wrote:

> On 16 August 2016 at 21:34, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> 
> > I see issuses with ZFS ARC inder memory pressure.
> > ZFS ARC size can be dramaticaly reduced, up to arc_min.
> >
> > As I see memory pressure event cause call arc_lowmem and set needfree:
> >
> > arc.c:arc_lowmem
> >
> >         needfree = btoc(arc_c >> arc_shrink_shift);
> >
> > After this, arc_available_memory return negative vaules (PAGESIZE *
> > (-needfree)) until needfree is zero. Independent how too much memory
> > freed. needfree set to 0 in arc_reclaim_thread(), when arc_size <=
> > arc_c. Until arc_size don't drop below arc_c (arc_c deceased at every
> > loop interation).
> >
> > arc_c droped to minimum value if arc_size fast enough droped.
> >
> > No control current to initial memory allocation.
> >
> > As result, I can see needless arc reclaim, from 10x to 100x times.
> >
> > Can some one check me and comment this?
> > _______________________________________________
> >
> 
> 
> What version are you on?

stable/10, same code in stable/11/9 and current/12

-- 
Slawa Olhovchenkov