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SubjectRe: [PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node basis
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On 06/21/2016 04:15 PM, Mel Gorman wrote:
> This patch makes reclaim decisions on a per-node basis. A reclaimer knows
> what zone is required by the allocation request and skips pages from
> higher zones. In many cases this will be ok because it's a GFP_HIGHMEM
> request of some description. On 64-bit, ZONE_DMA32 requests will cause
> some problems but 32-bit devices on 64-bit platforms are increasingly
> rare. Historically it would have been a major problem on 32-bit with big
> Highmem:Lowmem ratios but such configurations are also now rare and even
> where they exist, they are not encouraged. If it really becomes a problem,
> it'll manifest as very low reclaim efficiencies.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>

[...]

> @@ -2540,14 +2559,14 @@ static inline bool compaction_ready(struct zone *zone, int order, int classzone_
> * If a zone is deemed to be full of pinned pages then just give it a light
> * scan then give up on it.
> */
> -static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> +static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
> + enum zone_type classzone_idx)
> {
> struct zoneref *z;
> struct zone *zone;
> unsigned long nr_soft_reclaimed;
> unsigned long nr_soft_scanned;
> gfp_t orig_mask;
> - enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
>
> /*
> * If the number of buffer_heads in the machine exceeds the maximum
> @@ -2560,15 +2579,20 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
>
> for_each_zone_zonelist_nodemask(zone, z, zonelist,
> gfp_zone(sc->gfp_mask), sc->nodemask) {

Using sc->reclaim_idx could be faster/nicer here than gfp_zone()?
Although after "mm, vmscan: Update classzone_idx if buffer_heads_over_limit"
there would need to be a variable for the highmem adjusted value - maybe reuse
"requested_highidx"? Not important though.

> - enum zone_type classzone_idx;
> -
> if (!populated_zone(zone))
> continue;
>
> - classzone_idx = requested_highidx;
> + /*
> + * Note that reclaim_idx does not change as it is the highest
> + * zone reclaimed from which for empty zones is a no-op but
> + * classzone_idx is used by shrink_node to test if the slabs
> + * should be shrunk on a given node.
> + */
> while (!populated_zone(zone->zone_pgdat->node_zones +
> - classzone_idx))
> + classzone_idx)) {
> classzone_idx--;
> + continue;
> + }
>
> /*
> * Take care memory controller reclaiming has small influence
> @@ -2594,8 +2618,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> */
> if (IS_ENABLED(CONFIG_COMPACTION) &&
> sc->order > PAGE_ALLOC_COSTLY_ORDER &&
> - zonelist_zone_idx(z) <= requested_highidx &&
> - compaction_ready(zone, sc->order, requested_highidx)) {
> + zonelist_zone_idx(z) <= classzone_idx &&
> + compaction_ready(zone, sc->order, classzone_idx)) {
> sc->compaction_ready = true;
> continue;
> }
> @@ -2615,7 +2639,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
> /* need some check for avoid more shrink_zone() */
> }
>
> - shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
> + shrink_node(zone->zone_pgdat, sc, classzone_idx);
> }
>
> /*
> @@ -2647,6 +2671,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> int initial_priority = sc->priority;
> unsigned long total_scanned = 0;
> unsigned long writeback_threshold;
> + enum zone_type classzone_idx = sc->reclaim_idx;

Hmm, try_to_free_mem_cgroup_pages() seems to call this with sc->reclaim_idx not
explicitly inirialized (e.g. 0). And shrink_all_memory() as well. I probably
didn't check them in v6 and pointed out only try_to_free_pages() (which is now
OK), sorry.

> retry:
> delayacct_freepages_start();
>
> @@ -2657,7 +2682,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
> vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
> sc->priority);
> sc->nr_scanned = 0;
> - shrink_zones(zonelist, sc);
> + shrink_zones(zonelist, sc, classzone_idx);

Looks like classzone_idx here is only used here to pass to shrink_zones()
unchanged, which means it can just use it directly without a new param?


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