Messages in this thread | | | Date | Tue, 21 Feb 2012 15:01:25 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH] memcg: rework inactive_ratio logic |
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Johannes Weiner wrote: > On Wed, Feb 15, 2012 at 08:24:42PM +0400, Konstantin Khlebnikov wrote: >> This patch adds mem_cgroup->inactive_ratio calculated from hierarchical memory limit. >> It updated at each limit change before shrinking cgroup to this new limit. >> Ratios for all child cgroups are updated too, because parent limit can affect them. >> Update precedure can be greatly optimized if its performance becomes the problem. >> Inactive ratio for unlimited or huge limit does not matter, because we'll never hit it. >> >> At global reclaim always use global ratio from zone->inactive_ratio. >> At mem-cgroup reclaim use inactive_ratio from target memory cgroup, >> this is cgroup which hit its limit and cause this reclaimer invocation. >> >> Thus, global memory reclaimer will try to keep ratio for all lru lists in zone >> above one mark, this guarantee that total ratio in this zone will be above too. >> Meanwhile mem-cgroup will do the same thing for its lru lists in all zones, and >> for all lru lists in all sub-cgroups in hierarchy. >> >> Also this patch removes some redundant code. >> >> Signed-off-by: Konstantin Khlebnikov<khlebnikov@openvz.org> > > I don't think we should take the zone ratio when we then proceed to > scan a bunch of LRU lists that could individually be much smaller than > the zone. Especially since the ratio function is not a linear one. > > Otherwise the target ratios can be way too big for small lists, see > the comment above mm/page_alloc.c::calculate_zone_inactive_ratio(). > > Consequently, I also disagree on using sc->target_mem_cgroup. > > This whole mechanism is about balancing one specific pair of inactive > vs. an active list according their size. We shouldn't derive policy > from numbers that are not correlated to this size.
Ok, maybe then we can move this inactive_ratio calculation right into inactive_anon_is_low(). Then we can kill precalculated zone->inactive_ratio and calculate it every time, even in non-memcg case, because zone-size also not always correlate with anon lru size. Looks like int_sqrt() is fast enough for this.
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