[PATCH 04/27] mm, vmscan: Begin reclaiming pages on a per-node basis

Mel Gorman
2016-06-09T18:07:46Z

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>
---
mm/vmscan.c | 72 ++++++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 47 insertions(+), 25 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f87a5a0f8793..ab1b28e7e20a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -84,6 +84,9 @@ struct scan_control {
/* Scan (total_size >> priority) pages at once */
int priority;

+ /* The highest zone to isolate pages for reclaim from */
+ enum zone_type reclaim_idx;
+
unsigned int may_writepage:1;

/* Can mapped pages be reclaimed? */
@@ -1369,6 +1372,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct list_head *src = &lruvec->lists[lru];
unsigned long nr_taken = 0;
unsigned long scan;
+ LIST_HEAD(pages_skipped);

for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
!list_empty(src); scan++) {
@@ -1379,6 +1383,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,

VM_BUG_ON_PAGE(!PageLRU(page), page);

+ if (page_zonenum(page) > sc->reclaim_idx) {
+ list_move(&page->lru, &pages_skipped);
+ continue;
+ }
+
switch (__isolate_lru_page(page, mode)) {
case 0:
nr_taken += hpage_nr_pages(page);
@@ -1395,6 +1404,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
}
}

+ /*
+ * Splice any skipped pages to the start of the LRU list. Note that
+ * this disrupts the LRU order when reclaiming for lower zones but
+ * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
+ * scanning would soon rescan the same pages to skip and put the
+ * system at risk of premature OOM.
+ */
+ if (!list_empty(&pages_skipped))
+ list_splice(&pages_skipped, src);
*nr_scanned = scan;
trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
nr_taken, mode, is_file_lru(lru));
@@ -1557,7 +1575,7 @@ static int current_may_throttle(void)
}

/*
- * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
+ * shrink_inactive_list() is a helper for shrink_node(). It returns the number
* of reclaimed pages
*/
static noinline_for_stack unsigned long
@@ -2371,12 +2389,13 @@ static inline bool should_continue_reclaim(struct zone *zone,
}
}

-static bool shrink_zone(struct zone *zone, struct scan_control *sc,
- bool is_classzone)
+static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc,
+ enum zone_type classzone_idx)
{
struct reclaim_state *reclaim_state = current->reclaim_state;
unsigned long nr_reclaimed, nr_scanned;
bool reclaimable = false;
+ struct zone *zone = &pgdat->node_zones[classzone_idx];

do {
struct mem_cgroup *root = sc->target_mem_cgroup;
@@ -2408,7 +2427,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
shrink_zone_memcg(zone, memcg, sc, &lru_pages);
zone_lru_pages += lru_pages;

- if (memcg && is_classzone)
+ if (!global_reclaim(sc) && sc->reclaim_idx == classzone_idx)
shrink_slab(sc->gfp_mask, zone_to_nid(zone),
memcg, sc->nr_scanned - scanned,
lru_pages);
@@ -2439,7 +2458,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
* Shrink the slab caches in the same proportion that
* the eligible LRU pages were scanned.
*/
- if (global_reclaim(sc) && is_classzone)
+ if (global_reclaim(sc) && sc->reclaim_idx == classzone_idx)
shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
sc->nr_scanned - nr_scanned,
zone_lru_pages);
@@ -2516,14 +2535,14 @@ 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
@@ -2536,15 +2555,15 @@ 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) {
- enum zone_type classzone_idx;
-
if (!populated_zone(zone))
continue;

- classzone_idx = requested_highidx;
while (!populated_zone(zone->zone_pgdat->node_zones +
- classzone_idx))
+ classzone_idx)) {
+ sc->reclaim_idx--;
classzone_idx--;
+ continue;
+ }

/*
* Take care memory controller reclaiming has small influence
@@ -2570,8 +2589,8 @@ 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;
}
@@ -2591,7 +2610,7 @@ 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);
}

/*
@@ -2623,6 +2642,7 @@ 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 = gfp_zone(sc->gfp_mask);
retry:
delayacct_freepages_start();

@@ -2633,7 +2653,7 @@ 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);

total_scanned += sc->nr_scanned;
if (sc->nr_reclaimed >= sc->nr_to_reclaim)
@@ -3088,7 +3108,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
balance_gap, classzone_idx))
return true;

- shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
+ shrink_node(zone->zone_pgdat, sc, classzone_idx);

/* TODO: ANOMALY */
clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
@@ -3137,6 +3157,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
unsigned long nr_soft_scanned;
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
+ .reclaim_idx = MAX_NR_ZONES - 1,
.order = order,
.priority = DEF_PRIORITY,
.may_writepage = !laptop_mode,
@@ -3207,15 +3228,14 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
sc.may_writepage = 1;

/*
- * Now scan the zone in the dma->highmem direction, stopping
- * at the last zone which needs scanning.
- *
- * We do this because the page allocator works in the opposite
- * direction. This prevents the page allocator from allocating
- * pages behind kswapd's direction of progress, which would
- * cause too much scanning of the lower zones.
+ * Continue scanning in the highmem->dma direction stopping at
+ * the last zone which needs scanning. This may reclaim lowmem
+ * pages that are not necessary for zone balancing but it
+ * preserves LRU ordering. It is assumed that the bulk of
+ * allocation requests can use arbitrary zones with the
+ * possible exception of big highmem:lowmem configurations.
*/
- for (i = 0; i <= end_zone; i++) {
+ for (i = end_zone; i >= end_zone; i--) {
struct zone *zone = pgdat->node_zones + i;

if (!populated_zone(zone))
@@ -3226,6 +3246,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
continue;

sc.nr_scanned = 0;
+ sc.reclaim_idx = i;

nr_soft_scanned = 0;
/*
@@ -3674,6 +3695,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
.may_unmap = !!(zone_reclaim_mode & RECLAIM_UNMAP),
.may_swap = 1,
+ .reclaim_idx = zone_idx(zone),
};

cond_resched();
@@ -3693,7 +3715,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
* priorities until we have enough memory freed.
*/
do {
- shrink_zone(zone, &sc, true);
+ shrink_node(zone->zone_pgdat, &sc, zone_idx(zone));
} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
}

--
2.6.4