[RFC][PATCH 5/5] Memory controller soft limit reclaim on contention (v9)

Balbir Singh
2009-07-10T12:36:05Z

Feature: Implement reclaim from groups over their soft limit

From: Balbir Singh <balbir@linux.vnet.ibm.com>

Changelog v9 ..v8
1. Changed the order of css_tryget()
2. Don't need to check for excess being greater than ULONG_MAX anymore.

Changelog v8 ..v7
1. Soft limit reclaim takes an order parameter and does no reclaim for
order > 0. This ensures that we don't do double reclaim for order > 0
2. Make the data structures more scalable, move the reclaim logic
to a new function mem_cgroup_shrink_node_zone that does per node
per zone reclaim.
3. Reclaim has moved back to kswapd (balance_pgdat)

Changelog v7...v6
1. Refactored out reclaim_options patch into a separate patch
2. Added additional checks for all swap off condition in
mem_cgroup_hierarchical_reclaim()

Changelog v6...v5
1. Reclaim arguments to hierarchical reclaim have been merged into one
parameter called reclaim_options.
2. Check if we failed to reclaim from one cgroup during soft reclaim, if
so move on to the next one. This can be very useful if the zonelist
passed to soft limit reclaim has no allocations from the selected
memory cgroup
3. Coding style cleanups

Changelog v5...v4

1. Throttling is removed, earlier we throttled tasks over their soft limit
2. Reclaim has been moved back to __alloc_pages_internal, several experiments
and tests showed that it was the best place to reclaim memory. kswapd has
a different goal, that does not work with a single soft limit for the memory
cgroup.
3. Soft limit reclaim is more targetted and the pages reclaim depend on the
amount by which the soft limit is exceeded.

Changelog v4...v3
1. soft_reclaim is now called from balance_pgdat
2. soft_reclaim is aware of nodes and zones
3. A mem_cgroup will be throttled if it is undergoing soft limit reclaim
and at the same time trying to allocate pages and exceed its soft limit.
4. A new mem_cgroup_shrink_zone() routine has been added to shrink zones
particular to a mem cgroup.

Changelog v3...v2
1. Convert several arguments to hierarchical reclaim to flags, thereby
consolidating them
2. The reclaim for soft limits is now triggered from kswapd
3. try_to_free_mem_cgroup_pages() now accepts an optional zonelist argument

Changelog v2...v1
1. Added support for hierarchical soft limits

This patch allows reclaim from memory cgroups on contention (via the
direct reclaim path).

memory cgroup soft limit reclaim finds the group that exceeds its soft limit
by the largest number of pages and reclaims pages from it and then reinserts the
cgroup into its correct place in the rbtree.

Added additional checks to mem_cgroup_hierarchical_reclaim() to detect
long loops in case all swap is turned off. The code has been refactored
and the loop check (loop < 2) has been enhanced for soft limits. For soft
limits, we try to do more targetted reclaim. Instead of bailing out after
two loops, the routine now reclaims memory proportional to the size by
which the soft limit is exceeded. The proportion has been empirically
determined.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

include/linux/memcontrol.h | 11 ++
include/linux/swap.h | 5 +
mm/memcontrol.c | 213 +++++++++++++++++++++++++++++++++++++++++---
mm/vmscan.c | 45 +++++++++
4 files changed, 259 insertions(+), 15 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e46a073..5296675 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -118,6 +118,9 @@ static inline bool mem_cgroup_disabled(void)

extern bool mem_cgroup_oom_called(struct task_struct *task);
void mem_cgroup_update_mapped_file_stat(struct page *page, int val);
+unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
+ gfp_t gfp_mask, int nid,
+ int zid);
#else /* CONFIG_CGROUP_MEM_RES_CTLR */
struct mem_cgroup;

@@ -276,6 +279,14 @@ static inline void mem_cgroup_update_mapped_file_stat(struct page *page,
{
}

+static inline
+unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
+ gfp_t gfp_mask, int nid,
+ int zid, int priority)
+{
+ return 0;
+}
+
#endif /* CONFIG_CGROUP_MEM_CONT */

#endif /* _LINUX_MEMCONTROL_H */
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 6c990e6..4c78fea 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -217,6 +217,11 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
gfp_t gfp_mask, bool noswap,
unsigned int swappiness);
+extern unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
+ gfp_t gfp_mask, bool noswap,
+ unsigned int swappiness,
+ struct zone *zone,
+ int nid);
extern int __isolate_lru_page(struct page *page, int mode, int file);
extern unsigned long shrink_all_memory(unsigned long nr_pages);
extern int vm_swappiness;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1421576..1d85362 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -139,6 +139,8 @@ struct mem_cgroup_per_zone {
unsigned long long usage_in_excess;/* Set to the value by which */
/* the soft limit is exceeded*/
bool on_tree;
+ struct mem_cgroup *mem; /* Back pointer, we cannot */
+ /* use container_of */
};
/* Macro for accessing counter */
#define MEM_CGROUP_ZSTAT(mz, idx) ((mz)->count[(idx)])
@@ -228,6 +230,13 @@ struct mem_cgroup {
struct mem_cgroup_stat stat;
};

+/*
+ * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
+ * limit reclaim to prevent infinite loops, if they ever occur.
+ */
+#define MEM_CGROUP_MAX_RECLAIM_LOOPS (100)
+#define MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS (2)
+
enum charge_type {
MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
MEM_CGROUP_CHARGE_TYPE_MAPPED,
@@ -259,6 +268,8 @@ enum charge_type {
#define MEM_CGROUP_RECLAIM_NOSWAP (1 << MEM_CGROUP_RECLAIM_NOSWAP_BIT)
#define MEM_CGROUP_RECLAIM_SHRINK_BIT 0x1
#define MEM_CGROUP_RECLAIM_SHRINK (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
+#define MEM_CGROUP_RECLAIM_SOFT_BIT 0x2
+#define MEM_CGROUP_RECLAIM_SOFT (1 << MEM_CGROUP_RECLAIM_SOFT_BIT)

static void mem_cgroup_get(struct mem_cgroup *mem);
static void mem_cgroup_put(struct mem_cgroup *mem);
@@ -299,7 +310,7 @@ soft_limit_tree_from_page(struct page *page)
}

static void
-mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
+__mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
struct mem_cgroup_per_zone *mz,
struct mem_cgroup_tree_per_zone *mctz)
{
@@ -311,7 +322,6 @@ mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
return;

mz->usage_in_excess = res_counter_soft_limit_excess(&mem->res);
- spin_lock(&mctz->lock);
while (*p) {
parent = *p;
mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
@@ -328,6 +338,26 @@ mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
rb_link_node(&mz->tree_node, parent, p);
rb_insert_color(&mz->tree_node, &mctz->rb_root);
mz->on_tree = true;
+}
+
+static void
+__mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
+ struct mem_cgroup_per_zone *mz,
+ struct mem_cgroup_tree_per_zone *mctz)
+{
+ if (!mz->on_tree)
+ return;
+ rb_erase(&mz->tree_node, &mctz->rb_root);
+ mz->on_tree = false;
+}
+
+static void
+mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
+ struct mem_cgroup_per_zone *mz,
+ struct mem_cgroup_tree_per_zone *mctz)
+{
+ spin_lock(&mctz->lock);
+ __mem_cgroup_insert_exceeded(mem, mz, mctz);
spin_unlock(&mctz->lock);
}

@@ -337,8 +367,7 @@ mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
struct mem_cgroup_tree_per_zone *mctz)
{
spin_lock(&mctz->lock);
- rb_erase(&mz->tree_node, &mctz->rb_root);
- mz->on_tree = false;
+ __mem_cgroup_remove_exceeded(mem, mz, mctz);
spin_unlock(&mctz->lock);
}

@@ -410,6 +439,47 @@ static void mem_cgroup_remove_from_trees(struct mem_cgroup *mem)
}
}

+static inline unsigned long mem_cgroup_get_excess(struct mem_cgroup *mem)
+{
+ return res_counter_soft_limit_excess(&mem->res) >> PAGE_SHIFT;
+}
+
+static struct mem_cgroup_per_zone *
+__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
+{
+ struct rb_node *rightmost = NULL;
+ struct mem_cgroup_per_zone *mz = NULL;
+
+retry:
+ rightmost = rb_last(&mctz->rb_root);
+ if (!rightmost)
+ goto done; /* Nothing to reclaim from */
+
+ mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
+ /*
+ * Remove the node now but someone else can add it back,
+ * we will to add it back at the end of reclaim to its correct
+ * position in the tree.
+ */
+ __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
+ if (!res_counter_soft_limit_excess(&mz->mem->res) ||
+ !css_tryget(&mz->mem->css))
+ goto retry;
+done:
+ return mz;
+}
+
+static struct mem_cgroup_per_zone *
+mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
+{
+ struct mem_cgroup_per_zone *mz;
+
+ spin_lock(&mctz->lock);
+ mz = __mem_cgroup_largest_soft_limit_node(mctz);
+ spin_unlock(&mctz->lock);
+ return mz;
+}
+
static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
struct page_cgroup *pc,
bool charge)
@@ -1039,6 +1109,7 @@ mem_cgroup_select_victim(struct mem_cgroup *root_mem)
* If shrink==true, for avoiding to free too much, this returns immedieately.
*/
static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
+ struct zone *zone,
gfp_t gfp_mask,
unsigned long reclaim_options)
{
@@ -1047,23 +1118,49 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
int loop = 0;
bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP;
bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK;
+ bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT;
+ unsigned long excess = mem_cgroup_get_excess(root_mem);

/* If memsw_is_minimum==1, swap-out is of-no-use. */
if (root_mem->memsw_is_minimum)
noswap = true;

- while (loop < 2) {
+ while (1) {
victim = mem_cgroup_select_victim(root_mem);
- if (victim == root_mem)
+ if (victim == root_mem) {
loop++;
+ if (loop >= 2) {
+ /*
+ * If we have not been able to reclaim
+ * anything, it might because there are
+ * no reclaimable pages under this hierarchy
+ */
+ if (!check_soft || !total)
+ break;
+ /*
+ * We want to do more targetted reclaim.
+ * excess >> 2 is not to excessive so as to
+ * reclaim too much, nor too less that we keep
+ * coming back to reclaim from this cgroup
+ */
+ if (total >= (excess >> 2) ||
+ (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
+ break;
+ }
+ }
if (!mem_cgroup_local_usage(&victim->stat)) {
/* this cgroup's local usage == 0 */
css_put(&victim->css);
continue;
}
/* we use swappiness of local cgroup */
- ret = try_to_free_mem_cgroup_pages(victim, gfp_mask, noswap,
- get_swappiness(victim));
+ if (check_soft)
+ ret = mem_cgroup_shrink_node_zone(victim, gfp_mask,
+ noswap, get_swappiness(victim), zone,
+ zone->zone_pgdat->node_id);
+ else
+ ret = try_to_free_mem_cgroup_pages(victim, gfp_mask,
+ noswap, get_swappiness(victim));
css_put(&victim->css);
/*
* At shrinking usage, we can't check we should stop here or
@@ -1073,7 +1170,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
if (shrink)
return ret;
total += ret;
- if (mem_cgroup_check_under_limit(root_mem))
+ if (check_soft) {
+ if (res_counter_check_under_soft_limit(&root_mem->res))
+ return total;
+ } else if (mem_cgroup_check_under_limit(root_mem))
return 1 + total;
}
return total;
@@ -1208,8 +1308,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
if (!(gfp_mask & __GFP_WAIT))
goto nomem;

- ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
- flags);
+ ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
+ gfp_mask, flags);
if (ret)
continue;

@@ -2003,8 +2103,9 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
if (!ret)
break;

- progress = mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL,
- MEM_CGROUP_RECLAIM_SHRINK);
+ progress = mem_cgroup_hierarchical_reclaim(memcg, NULL,
+ GFP_KERNEL,
+ MEM_CGROUP_RECLAIM_SHRINK);
curusage = res_counter_read_u64(&memcg->res, RES_USAGE);
/* Usage is reduced ? */
if (curusage >= oldusage)
@@ -2056,7 +2157,7 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
if (!ret)
break;

- mem_cgroup_hierarchical_reclaim(memcg, GFP_KERNEL,
+ mem_cgroup_hierarchical_reclaim(memcg, NULL, GFP_KERNEL,
MEM_CGROUP_RECLAIM_NOSWAP |
MEM_CGROUP_RECLAIM_SHRINK);
curusage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
@@ -2069,6 +2170,88 @@ static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
return ret;
}

+unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
+ gfp_t gfp_mask, int nid,
+ int zid)
+{
+ unsigned long nr_reclaimed = 0;
+ struct mem_cgroup_per_zone *mz, *next_mz = NULL;
+ unsigned long reclaimed;
+ int loop = 0;
+ struct mem_cgroup_tree_per_zone *mctz;
+
+ if (order > 0)
+ return 0;
+
+ mctz = soft_limit_tree_node_zone(nid, zid);
+ /*
+ * This loop can run a while, specially if mem_cgroup's continuously
+ * keep exceeding their soft limit and putting the system under
+ * pressure
+ */
+ do {
+ if (next_mz)
+ mz = next_mz;
+ else
+ mz = mem_cgroup_largest_soft_limit_node(mctz);
+ if (!mz)
+ break;
+
+ reclaimed = mem_cgroup_hierarchical_reclaim(mz->mem, zone,
+ gfp_mask,
+ MEM_CGROUP_RECLAIM_SOFT);
+ nr_reclaimed += reclaimed;
+ spin_lock(&mctz->lock);
+
+ /*
+ * If we failed to reclaim anything from this memory cgroup
+ * it is time to move on to the next cgroup
+ */
+ next_mz = NULL;
+ if (!reclaimed) {
+ do {
+ /*
+ * By the time we get the soft_limit lock
+ * again, someone might have aded the
+ * group back on the RB tree. Iterate to
+ * make sure we get a different mem.
+ * mem_cgroup_largest_soft_limit_node returns
+ * NULL if no other cgroup is present on
+ * the tree
+ */
+ next_mz =
+ __mem_cgroup_largest_soft_limit_node(mctz);
+ } while (next_mz == mz);
+ }
+ mz->usage_in_excess =
+ res_counter_soft_limit_excess(&mz->mem->res);
+ __mem_cgroup_remove_exceeded(mz->mem, mz, mctz);
+ /*
+ * One school of thought says that we should not add
+ * back the node to the tree if reclaim returns 0.
+ * But our reclaim could return 0, simply because due
+ * to priority we are exposing a smaller subset of
+ * memory to reclaim from. Consider this as a longer
+ * term TODO.
+ */
+ if (mz->usage_in_excess)
+ __mem_cgroup_insert_exceeded(mz->mem, mz, mctz);
+ spin_unlock(&mctz->lock);
+ css_put(&mz->mem->css);
+ loop++;
+ /*
+ * Could not reclaim anything and there are no more
+ * mem cgroups to try or we seem to be looping without
+ * reclaiming anything.
+ */
+ if (!nr_reclaimed &&
+ (next_mz == NULL ||
+ loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
+ break;
+ } while (!nr_reclaimed);
+ return nr_reclaimed;
+}
+
/*
* This routine traverse page_cgroup in given list and drop them all.
* *And* this routine doesn't reclaim page itself, just removes page_cgroup.
@@ -2671,6 +2854,8 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
for_each_lru(l)
INIT_LIST_HEAD(&mz->lists[l]);
mz->usage_in_excess = 0;
+ mz->on_tree = false;
+ mz->mem = mem;
}
return 0;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 86dc0c3..3e95aca 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1780,11 +1780,45 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,

#ifdef CONFIG_CGROUP_MEM_RES_CTLR

+unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
+ gfp_t gfp_mask, bool noswap,
+ unsigned int swappiness,
+ struct zone *zone, int nid)
+{
+ struct scan_control sc = {
+ .may_writepage = !laptop_mode,
+ .may_unmap = 1,
+ .may_swap = !noswap,
+ .swap_cluster_max = SWAP_CLUSTER_MAX,
+ .swappiness = swappiness,
+ .order = 0,
+ .mem_cgroup = mem,
+ .isolate_pages = mem_cgroup_isolate_pages,
+ };
+ nodemask_t nm = nodemask_of_node(nid);
+
+ sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
+ (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
+ sc.nodemask = &nm;
+ sc.nr_reclaimed = 0;
+ sc.nr_scanned = 0;
+ /*
+ * NOTE: Although we can get the priority field, using it
+ * here is not a good idea, since it limits the pages we can scan.
+ * if we don't reclaim here, the shrink_zone from balance_pgdat
+ * will pick up pages from other mem cgroup's as well. We hack
+ * the priority and make it zero.
+ */
+ shrink_zone(0, zone, &sc);
+ return sc.nr_reclaimed;
+}
+
unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
gfp_t gfp_mask,
bool noswap,
unsigned int swappiness)
{
+ struct zonelist *zonelist;
struct scan_control sc = {
.may_writepage = !laptop_mode,
.may_unmap = 1,
@@ -1796,7 +1830,6 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
.isolate_pages = mem_cgroup_isolate_pages,
.nodemask = NULL, /* we don't care the placement */
};
- struct zonelist *zonelist;

sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
@@ -1918,6 +1951,7 @@ loop_again:
for (i = 0; i <= end_zone; i++) {
struct zone *zone = pgdat->node_zones + i;
int nr_slab;
+ int nid, zid;

if (!populated_zone(zone))
continue;
@@ -1932,6 +1966,15 @@ loop_again:
temp_priority[i] = priority;
sc.nr_scanned = 0;
note_zone_scanning_priority(zone, priority);
+
+ nid = pgdat->node_id;
+ zid = zone_idx(zone);
+ /*
+ * Call soft limit reclaim before calling shrink_zone.
+ * For now we ignore the return value
+ */
+ mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask,
+ nid, zid);
/*
* We put equal pressure on every zone, unless one
* zone has way too many pages free already.