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mm, vmscan: make kswapd reclaim in terms of nodes

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Patch "mm: vmscan: Begin reclaiming pages on a per-node basis" started
thinking of reclaim in terms of nodes but kswapd is still zone-centric.
This patch gets rid of many of the node-based versus zone-based
decisions.

o A node is considered balanced when any eligible lower zone is balanced.
  This eliminates one class of age-inversion problem because we avoid
  reclaiming a newer page just because it's in the wrong zone
o pgdat_balanced disappears because we now only care about one zone being
  balanced.
o Some anomalies related to writeback and congestion tracking being based on
  zones disappear.
o kswapd no longer has to take care to reclaim zones in the reverse order
  that the page allocator uses.
o Most importantly of all, reclaim from node 0 with multiple zones will
  have similar aging and reclaiming characteristics as every
  other node.

Link: http://lkml.kernel.org/r/1467970510-21195-8-git-send-email-mgorman@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2016-07-28 15:45:43 -07:00 committed by Linus Torvalds
parent f7b60926eb
commit 1d82de618d
1 changed files with 106 additions and 196 deletions
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302
mm/vmscan.c
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@ -2980,7 +2980,8 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
}
#endif
static void age_active_anon(struct zone *zone, struct scan_control *sc)
static void age_active_anon(struct pglist_data *pgdat,
struct zone *zone, struct scan_control *sc)
{
struct mem_cgroup *memcg;
@ -2999,84 +3000,14 @@ static void age_active_anon(struct zone *zone, struct scan_control *sc)
} while (memcg);
}
static bool zone_balanced(struct zone *zone, int order, bool highorder,
static bool zone_balanced(struct zone *zone, int order,
unsigned long balance_gap, int classzone_idx)
{
unsigned long mark = high_wmark_pages(zone) + balance_gap;
/*
* When checking from pgdat_balanced(), kswapd should stop and sleep
* when it reaches the high order-0 watermark and let kcompactd take
* over. Other callers such as wakeup_kswapd() want to determine the
* true high-order watermark.
*/
if (IS_ENABLED(CONFIG_COMPACTION) && !highorder) {
mark += (1UL << order);
order = 0;
}
return zone_watermark_ok_safe(zone, order, mark, classzone_idx);
}
/*
* pgdat_balanced() is used when checking if a node is balanced.
*
* For order-0, all zones must be balanced!
*
* For high-order allocations only zones that meet watermarks and are in a
* zone allowed by the callers classzone_idx are added to balanced_pages. The
* total of balanced pages must be at least 25% of the zones allowed by
* classzone_idx for the node to be considered balanced. Forcing all zones to
* be balanced for high orders can cause excessive reclaim when there are
* imbalanced zones.
* The choice of 25% is due to
* o a 16M DMA zone that is balanced will not balance a zone on any
* reasonable sized machine
* o On all other machines, the top zone must be at least a reasonable
* percentage of the middle zones. For example, on 32-bit x86, highmem
* would need to be at least 256M for it to be balance a whole node.
* Similarly, on x86-64 the Normal zone would need to be at least 1G
* to balance a node on its own. These seemed like reasonable ratios.
*/
static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
{
unsigned long managed_pages = 0;
unsigned long balanced_pages = 0;
int i;
/* Check the watermark levels */
for (i = 0; i <= classzone_idx; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
managed_pages += zone->managed_pages;
/*
* A special case here:
*
* balance_pgdat() skips over all_unreclaimable after
* DEF_PRIORITY. Effectively, it considers them balanced so
* they must be considered balanced here as well!
*/
if (!pgdat_reclaimable(zone->zone_pgdat)) {
balanced_pages += zone->managed_pages;
continue;
}
if (zone_balanced(zone, order, false, 0, i))
balanced_pages += zone->managed_pages;
else if (!order)
return false;
}
if (order)
return balanced_pages >= (managed_pages >> 2);
else
return true;
}
/*
* Prepare kswapd for sleeping. This verifies that there are no processes
* waiting in throttle_direct_reclaim() and that watermarks have been met.
@ -3086,6 +3017,8 @@ static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
int classzone_idx)
{
int i;
/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
if (remaining)
return false;
@ -3106,101 +3039,90 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
if (waitqueue_active(&pgdat->pfmemalloc_wait))
wake_up_all(&pgdat->pfmemalloc_wait);
return pgdat_balanced(pgdat, order, classzone_idx);
for (i = 0; i <= classzone_idx; i++) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone_balanced(zone, order, 0, classzone_idx))
return true;
}
return false;
}
/*
* kswapd shrinks the zone by the number of pages required to reach
* the high watermark.
* kswapd shrinks a node of pages that are at or below the highest usable
* zone that is currently unbalanced.
*
* Returns true if kswapd scanned at least the requested number of pages to
* reclaim or if the lack of progress was due to pages under writeback.
* This is used to determine if the scanning priority needs to be raised.
*/
static bool kswapd_shrink_zone(struct zone *zone,
static bool kswapd_shrink_node(pg_data_t *pgdat,
int classzone_idx,
struct scan_control *sc)
{
unsigned long balance_gap;
bool lowmem_pressure;
struct pglist_data *pgdat = zone->zone_pgdat;
struct zone *zone;
int z;
/* Reclaim above the high watermark. */
sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
/* Reclaim a number of pages proportional to the number of zones */
sc->nr_to_reclaim = 0;
for (z = 0; z <= classzone_idx; z++) {
zone = pgdat->node_zones + z;
if (!populated_zone(zone))
continue;
/*
* We put equal pressure on every zone, unless one zone has way too
* many pages free already. The "too many pages" is defined as the
* high wmark plus a "gap" where the gap is either the low
* watermark or 1% of the zone, whichever is smaller.
*/
balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
/*
* If there is no low memory pressure or the zone is balanced then no
* reclaim is necessary
*/
lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
if (!lowmem_pressure && zone_balanced(zone, sc->order, false,
balance_gap, classzone_idx))
return true;
shrink_node(zone->zone_pgdat, sc, classzone_idx);
/* TODO: ANOMALY */
clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
/*
* If a zone reaches its high watermark, consider it to be no longer
* congested. It's possible there are dirty pages backed by congested
* BDIs but as pressure is relieved, speculatively avoid congestion
* waits.
*/
if (pgdat_reclaimable(zone->zone_pgdat) &&
zone_balanced(zone, sc->order, false, 0, classzone_idx)) {
clear_bit(PGDAT_CONGESTED, &pgdat->flags);
clear_bit(PGDAT_DIRTY, &pgdat->flags);
sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
}
/*
* Historically care was taken to put equal pressure on all zones but
* now pressure is applied based on node LRU order.
*/
shrink_node(pgdat, sc, classzone_idx);
/*
* Fragmentation may mean that the system cannot be rebalanced for
* high-order allocations. If twice the allocation size has been
* reclaimed then recheck watermarks only at order-0 to prevent
* excessive reclaim. Assume that a process requested a high-order
* can direct reclaim/compact.
*/
if (sc->order && sc->nr_reclaimed >= 2UL << sc->order)
sc->order = 0;
return sc->nr_scanned >= sc->nr_to_reclaim;
}
/*
* For kswapd, balance_pgdat() will work across all this node's zones until
* they are all at high_wmark_pages(zone).
* For kswapd, balance_pgdat() will reclaim pages across a node from zones
* that are eligible for use by the caller until at least one zone is
* balanced.
*
* Returns the highest zone idx kswapd was reclaiming at
*
* There is special handling here for zones which are full of pinned pages.
* This can happen if the pages are all mlocked, or if they are all used by
* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
* What we do is to detect the case where all pages in the zone have been
* scanned twice and there has been zero successful reclaim. Mark the zone as
* dead and from now on, only perform a short scan. Basically we're polling
* the zone for when the problem goes away.
* Returns the order kswapd finished reclaiming at.
*
* kswapd scans the zones in the highmem->normal->dma direction. It skips
* zones which have free_pages > high_wmark_pages(zone), but once a zone is
* found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
* lower zones regardless of the number of free pages in the lower zones. This
* interoperates with the page allocator fallback scheme to ensure that aging
* of pages is balanced across the zones.
* found to have free_pages <= high_wmark_pages(zone), any page is that zone
* or lower is eligible for reclaim until at least one usable zone is
* balanced.
*/
static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
{
int i;
int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
unsigned long nr_soft_reclaimed;
unsigned long nr_soft_scanned;
struct zone *zone;
struct scan_control sc = {
.gfp_mask = GFP_KERNEL,
.reclaim_idx = MAX_NR_ZONES - 1,
.order = order,
.priority = DEF_PRIORITY,
.may_writepage = !laptop_mode,
.may_unmap = 1,
.may_swap = 1,
.reclaim_idx = classzone_idx,
};
count_vm_event(PAGEOUTRUN);
@ -3211,21 +3133,10 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
/* Scan from the highest requested zone to dma */
for (i = classzone_idx; i >= 0; i--) {
struct zone *zone = pgdat->node_zones + i;
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (sc.priority != DEF_PRIORITY &&
!pgdat_reclaimable(zone->zone_pgdat))
continue;
/*
* Do some background aging of the anon list, to give
* pages a chance to be referenced before reclaiming.
*/
age_active_anon(zone, &sc);
/*
* If the number of buffer_heads in the machine
* exceeds the maximum allowed level and this node
@ -3233,19 +3144,17 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
* it to relieve lowmem pressure.
*/
if (buffer_heads_over_limit && is_highmem_idx(i)) {
end_zone = i;
classzone_idx = i;
break;
}
if (!zone_balanced(zone, order, false, 0, 0)) {
end_zone = i;
if (!zone_balanced(zone, order, 0, 0)) {
classzone_idx = i;
break;
} else {
/*
* If balanced, clear the dirty and congested
* flags
*
* TODO: ANOMALY
* If any eligible zone is balanced then the
* node is not considered congested or dirty.
*/
clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
@ -3255,52 +3164,35 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
if (i < 0)
goto out;
/*
* Do some background aging of the anon list, to give
* pages a chance to be referenced before reclaiming. All
* pages are rotated regardless of classzone as this is
* about consistent aging.
*/
age_active_anon(pgdat, &pgdat->node_zones[MAX_NR_ZONES - 1], &sc);
/*
* If we're getting trouble reclaiming, start doing writepage
* even in laptop mode.
*/
if (sc.priority < DEF_PRIORITY - 2)
if (sc.priority < DEF_PRIORITY - 2 || !pgdat_reclaimable(pgdat))
sc.may_writepage = 1;
/* Call soft limit reclaim before calling shrink_node. */
sc.nr_scanned = 0;
nr_soft_scanned = 0;
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, sc.order,
sc.gfp_mask, &nr_soft_scanned);
sc.nr_reclaimed += nr_soft_reclaimed;
/*
* 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.
* There should be no need to raise the scanning priority if
* enough pages are already being scanned that that high
* watermark would be met at 100% efficiency.
*/
for (i = end_zone; i >= 0; i--) {
struct zone *zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (sc.priority != DEF_PRIORITY &&
!pgdat_reclaimable(zone->zone_pgdat))
continue;
sc.nr_scanned = 0;
sc.reclaim_idx = i;
nr_soft_scanned = 0;
/*
* Call soft limit reclaim before calling shrink_zone.
*/
nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
order, sc.gfp_mask,
&nr_soft_scanned);
sc.nr_reclaimed += nr_soft_reclaimed;
/*
* There should be no need to raise the scanning
* priority if enough pages are already being scanned
* that that high watermark would be met at 100%
* efficiency.
*/
if (kswapd_shrink_zone(zone, end_zone, &sc))
raise_priority = false;
}
if (kswapd_shrink_node(pgdat, classzone_idx, &sc))
raise_priority = false;
/*
* If the low watermark is met there is no need for processes
@ -3315,21 +3207,38 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
if (try_to_freeze() || kthread_should_stop())
break;
/*
* Stop reclaiming if any eligible zone is balanced and clear
* node writeback or congested.
*/
for (i = 0; i <= classzone_idx; i++) {
zone = pgdat->node_zones + i;
if (!populated_zone(zone))
continue;
if (zone_balanced(zone, sc.order, 0, classzone_idx)) {
clear_bit(PGDAT_CONGESTED, &pgdat->flags);
clear_bit(PGDAT_DIRTY, &pgdat->flags);
goto out;
}
}
/*
* Raise priority if scanning rate is too low or there was no
* progress in reclaiming pages
*/
if (raise_priority || !sc.nr_reclaimed)
sc.priority--;
} while (sc.priority >= 1 &&
!pgdat_balanced(pgdat, order, classzone_idx));
} while (sc.priority >= 1);
out:
/*
* Return the highest zone idx we were reclaiming at so
* prepare_kswapd_sleep() makes the same decisions as here.
* Return the order kswapd stopped reclaiming at as
* prepare_kswapd_sleep() takes it into account. If another caller
* entered the allocator slow path while kswapd was awake, order will
* remain at the higher level.
*/
return end_zone;
return sc.order;
}
static void kswapd_try_to_sleep(pg_data_t *pgdat, int order,
@ -3486,8 +3395,9 @@ static int kswapd(void *p)
*/
if (!ret) {
trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
balanced_classzone_idx = balance_pgdat(pgdat, order,
classzone_idx);
/* return value ignored until next patch */
balance_pgdat(pgdat, order, classzone_idx);
}
}
@ -3517,7 +3427,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
}
if (!waitqueue_active(&pgdat->kswapd_wait))
return;
if (zone_balanced(zone, order, true, 0, 0))
if (zone_balanced(zone, order, 0, 0))
return;
trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);