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

Mel Gorman
2009-04-21T09:47:04Z

On Tue, Apr 21, 2009 at 03:52:48PM +0900, KOSAKI Motohiro 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>
> > ---
> > include/linux/cpuset.h | 2 ++
> > mm/page_alloc.c | 37 ++++++++++++++++++++++++++-----------
> > 2 files changed, 28 insertions(+), 11 deletions(-)
> >
> > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> > index a5740fc..978e2f1 100644
> > --- a/include/linux/cpuset.h
> > +++ b/include/linux/cpuset.h
> > @@ -97,6 +97,8 @@ static inline void set_mems_allowed(nodemask_t nodemask)
> >
> > #else /* !CONFIG_CPUSETS */
> >
> > +#define number_of_cpusets (0)
> > +
> > static inline int cpuset_init(void) { return 0; }
> > static inline void cpuset_init_smp(void) {}
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c8465d0..3613ba4 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1137,7 +1137,11 @@ failed:
> > #define ALLOC_WMARK_HIGH 0x08 /* use pages_high watermark */
> > #define ALLOC_HARDER 0x10 /* try to alloc harder */
> > #define ALLOC_HIGH 0x20 /* __GFP_HIGH set */
> > +#ifdef CONFIG_CPUSETS
> > #define ALLOC_CPUSET 0x40 /* check for correct cpuset */
> > +#else
> > +#define ALLOC_CPUSET 0x00
> > +#endif /* CONFIG_CPUSETS */
> >
> > #ifdef CONFIG_FAIL_PAGE_ALLOC
> >
> > @@ -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) &&
> > + !cpuset_zone_allowed_softwall(zone, gfp_mask))
> > + goto try_next_zone;
> > + }
>
> if number_of_cpusets==1, old code call zlc_zone_worth_trying(). but your one never call.
> it seems regression.
>

True, but once fixed, the patch becomes a lot less useful. The intention was
to avoid the zlc_setup() function which is pretty heavy and hits on HIGHMEM
machines quite easily but I did it wrong. I should have made the
decision to only call zlc_setup() when there were online NUMA nodes to
care about.

I'll drop this patch and try again.

>
> >
> > if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
> > unsigned long mark;
> > @@ -1445,13 +1458,15 @@ zonelist_scan:
> > if (page)
> > break;
> > this_zone_full:
> > - if (NUMA_BUILD)
> > + if (NUMA_BUILD && zonelist_filter)
> > zlc_mark_zone_full(zonelist, z);
> > try_next_zone:
> > - if (NUMA_BUILD && !did_zlc_setup) {
> > - /* we do zlc_setup after the first zone is tried */
> > - allowednodes = zlc_setup(zonelist, alloc_flags);
> > - zlc_active = 1;
> > + if (NUMA_BUILD && zonelist_filter) {
> > + if (!did_zlc_setup) {
> > + /* do zlc_setup after the first zone is tried */
> > + allowednodes = zlc_setup(zonelist, alloc_flags);
> > + zlc_active = 1;
> > + }
> > did_zlc_setup = 1;
> > }
> > }
> > --
> > 1.5.6.5
> >
> > --
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> > see: http://www.linux-mm.org/ .
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>
>
>

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