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

Pekka Enberg
2009-04-21T07:20:56Z

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?

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