Re: [PATCH 07/25] Check in advance if the zonelist needs additional filtering

Mel Gorman
2009-04-21T09:49:15Z

On Tue, Apr 21, 2009 at 10:21:12AM +0300, Pekka Enberg wrote:
> Hi Mel,
>
> On Mon, 2009-04-20 at 23:19 +0100, Mel Gorman wrote:
> > Zonelist are filtered based on nodemasks for memory policies normally.
> > It can be additionally filters on cpusets if they exist as well as
> > noting when zones are full. These simple checks are expensive enough to
> > be noticed in profiles. This patch checks in advance if zonelist
> > filtering will ever be needed. If not, then the bulk of the checks are
> > skipped.
> >
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > @@ -1401,6 +1405,7 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
> > nodemask_t *allowednodes = NULL;/* zonelist_cache approximation */
> > int zlc_active = 0; /* set if using zonelist_cache */
> > int did_zlc_setup = 0; /* just call zlc_setup() one time */
> > + int zonelist_filter = 0;
> >
> > (void)first_zones_zonelist(zonelist, high_zoneidx, nodemask,
> > &preferred_zone);
> > @@ -1411,6 +1416,10 @@ get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
> >
> > VM_BUG_ON(order >= MAX_ORDER);
> >
> > + /* Determine in advance if the zonelist needs filtering */
> > + if ((alloc_flags & ALLOC_CPUSET) && unlikely(number_of_cpusets > 1))
> > + zonelist_filter = 1;
> > +
> > zonelist_scan:
> > /*
> > * Scan zonelist, looking for a zone with enough free.
> > @@ -1418,12 +1427,16 @@ zonelist_scan:
> > */
> > for_each_zone_zonelist_nodemask(zone, z, zonelist,
> > high_zoneidx, nodemask) {
> > - if (NUMA_BUILD && zlc_active &&
> > - !zlc_zone_worth_trying(zonelist, z, allowednodes))
> > - continue;
> > - if ((alloc_flags & ALLOC_CPUSET) &&
> > - !cpuset_zone_allowed_softwall(zone, gfp_mask))
> > - goto try_next_zone;
> > +
> > + /* Ignore the additional zonelist filter checks if possible */
> > + if (zonelist_filter) {
> > + if (NUMA_BUILD && zlc_active &&
> > + !zlc_zone_worth_trying(zonelist, z, allowednodes))
> > + continue;
> > + if ((alloc_flags & ALLOC_CPUSET) &&
>
> The above expression is always true here because of the earlier
> zonelists_filter check, no?
>

Yeah, silly. I've dropped the patch altogether though because it was
avoiding zonelist filtering for the wrong reasons.

> > + !cpuset_zone_allowed_softwall(zone, gfp_mask))
> > + goto try_next_zone;
> > + }
> >
> > if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
> > unsigned long mark;
>
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab