The patch titled
Subject: mm/memcg: optimize user context object stock access
has been added to the -mm tree. Its filename is
mm-memcg-optimize-user-context-object-stock-access.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-optimize-user-context-object-stock-access.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-optimize-user-context-object-stock-access.patch
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
Subject: mm/memcg: optimize user context object stock access
Most kmem_cache_alloc() calls are from user context. With instrumentation
enabled, the measured amount of kmem_cache_alloc() calls from non-task
context was about 0.01% of the total.
The irq disable/enable sequence used in this case to access content from
object stock is slow. To optimize for user context access, there are now
two sets of object stocks (in the new obj_stock structure) for task
context and interrupt context access respectively.
The task context object stock can be accessed after disabling preemption
which is cheap in non-preempt kernel. The interrupt context object stock
can only be accessed after disabling interrupt. User context code can
access interrupt object stock, but not vice versa.
The downside of this change is that there are more data stored in local
object stocks and not reflected in the charge counter and the vmstat
arrays. However, this is a small price to pay for better performance.
Link: https://lkml.kernel.org/r/20210506150007.16288-5-longman@xxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Roman Gushchin <guro@xxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Chris Down <chris@xxxxxxxxxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>
Cc: Xing Zhengjun <zhengjun.xing@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 94 +++++++++++++++++++++++++++++++++-------------
1 file changed, 68 insertions(+), 26 deletions(-)
--- a/mm/memcontrol.c~mm-memcg-optimize-user-context-object-stock-access
+++ a/mm/memcontrol.c
@@ -782,6 +782,10 @@ void __mod_lruvec_kmem_state(void *p, en
rcu_read_unlock();
}
+/*
+ * mod_objcg_mlstate() may be called with irq enabled, so
+ * mod_memcg_lruvec_state() should be used.
+ */
static inline void mod_objcg_mlstate(struct obj_cgroup *objcg,
struct pglist_data *pgdat,
enum node_stat_item idx, int nr)
@@ -792,7 +796,7 @@ static inline void mod_objcg_mlstate(str
rcu_read_lock();
memcg = obj_cgroup_memcg(objcg);
lruvec = mem_cgroup_lruvec(memcg, pgdat);
- __mod_memcg_lruvec_state(lruvec, idx, nr);
+ mod_memcg_lruvec_state(lruvec, idx, nr);
rcu_read_unlock();
}
@@ -2054,17 +2058,23 @@ void unlock_page_memcg(struct page *page
}
EXPORT_SYMBOL(unlock_page_memcg);
-struct memcg_stock_pcp {
- struct mem_cgroup *cached; /* this never be root cgroup */
- unsigned int nr_pages;
-
+struct obj_stock {
#ifdef CONFIG_MEMCG_KMEM
struct obj_cgroup *cached_objcg;
struct pglist_data *cached_pgdat;
unsigned int nr_bytes;
int nr_slab_reclaimable_b;
int nr_slab_unreclaimable_b;
+#else
+ int dummy[0];
#endif
+};
+
+struct memcg_stock_pcp {
+ struct mem_cgroup *cached; /* this never be root cgroup */
+ unsigned int nr_pages;
+ struct obj_stock task_obj;
+ struct obj_stock irq_obj;
struct work_struct work;
unsigned long flags;
@@ -2074,12 +2084,12 @@ static DEFINE_PER_CPU(struct memcg_stock
static DEFINE_MUTEX(percpu_charge_mutex);
#ifdef CONFIG_MEMCG_KMEM
-static void drain_obj_stock(struct memcg_stock_pcp *stock);
+static void drain_obj_stock(struct obj_stock *stock);
static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
struct mem_cgroup *root_memcg);
#else
-static inline void drain_obj_stock(struct memcg_stock_pcp *stock)
+static inline void drain_obj_stock(struct obj_stock *stock)
{
}
static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
@@ -2089,6 +2099,40 @@ static bool obj_stock_flush_required(str
}
#endif
+/*
+ * Most kmem_cache_alloc() calls are from user context. The irq disable/enable
+ * sequence used in this case to access content from object stock is slow.
+ * To optimize for user context access, there are now two object stocks for
+ * task context and interrupt context access respectively.
+ *
+ * The task context object stock can be accessed by disabling preemption only
+ * which is cheap in non-preempt kernel. The interrupt context object stock
+ * can only be accessed after disabling interrupt. User context code can
+ * access interrupt object stock, but not vice versa.
+ */
+static inline struct obj_stock *get_obj_stock(unsigned long *pflags)
+{
+ struct memcg_stock_pcp *stock;
+
+ if (likely(in_task())) {
+ preempt_disable();
+ stock = this_cpu_ptr(&memcg_stock);
+ return &stock->task_obj;
+ } else {
+ local_irq_save(*pflags);
+ stock = this_cpu_ptr(&memcg_stock);
+ return &stock->irq_obj;
+ }
+}
+
+static inline void put_obj_stock(unsigned long flags)
+{
+ if (likely(in_task()))
+ preempt_enable();
+ else
+ local_irq_restore(flags);
+}
+
/**
* consume_stock: Try to consume stocked charge on this cpu.
* @memcg: memcg to consume from.
@@ -2155,7 +2199,9 @@ static void drain_local_stock(struct wor
local_irq_save(flags);
stock = this_cpu_ptr(&memcg_stock);
- drain_obj_stock(stock);
+ drain_obj_stock(&stock->irq_obj);
+ if (in_task())
+ drain_obj_stock(&stock->task_obj);
drain_stock(stock);
clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
@@ -3015,13 +3061,10 @@ void __memcg_kmem_uncharge_page(struct p
void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
enum node_stat_item idx, int nr)
{
- struct memcg_stock_pcp *stock;
unsigned long flags;
+ struct obj_stock *stock = get_obj_stock(&flags);
int *bytes;
- local_irq_save(flags);
- stock = this_cpu_ptr(&memcg_stock);
-
/*
* Save vmstat data in stock and skip vmstat array update unless
* accumulating over a page of vmstat data or when pgdat or idx
@@ -3070,29 +3113,26 @@ void mod_objcg_state(struct obj_cgroup *
if (nr)
mod_objcg_mlstate(objcg, pgdat, idx, nr);
- local_irq_restore(flags);
+ put_obj_stock(flags);
}
static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
{
- struct memcg_stock_pcp *stock;
unsigned long flags;
+ struct obj_stock *stock = get_obj_stock(&flags);
bool ret = false;
- local_irq_save(flags);
-
- stock = this_cpu_ptr(&memcg_stock);
if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
stock->nr_bytes -= nr_bytes;
ret = true;
}
- local_irq_restore(flags);
+ put_obj_stock(flags);
return ret;
}
-static void drain_obj_stock(struct memcg_stock_pcp *stock)
+static void drain_obj_stock(struct obj_stock *stock)
{
struct obj_cgroup *old = stock->cached_objcg;
@@ -3148,8 +3188,13 @@ static bool obj_stock_flush_required(str
{
struct mem_cgroup *memcg;
- if (stock->cached_objcg) {
- memcg = obj_cgroup_memcg(stock->cached_objcg);
+ if (in_task() && stock->task_obj.cached_objcg) {
+ memcg = obj_cgroup_memcg(stock->task_obj.cached_objcg);
+ if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
+ return true;
+ }
+ if (stock->irq_obj.cached_objcg) {
+ memcg = obj_cgroup_memcg(stock->irq_obj.cached_objcg);
if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
return true;
}
@@ -3160,13 +3205,10 @@ static bool obj_stock_flush_required(str
static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
bool allow_uncharge)
{
- struct memcg_stock_pcp *stock;
unsigned long flags;
+ struct obj_stock *stock = get_obj_stock(&flags);
unsigned int nr_pages = 0;
- local_irq_save(flags);
-
- stock = this_cpu_ptr(&memcg_stock);
if (stock->cached_objcg != objcg) { /* reset if necessary */
drain_obj_stock(stock);
obj_cgroup_get(objcg);
@@ -3182,7 +3224,7 @@ static void refill_obj_stock(struct obj_
stock->nr_bytes &= (PAGE_SIZE - 1);
}
- local_irq_restore(flags);
+ put_obj_stock(flags);
if (nr_pages)
obj_cgroup_uncharge_pages(objcg, nr_pages);
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
mm-memcg-move-mod_objcg_state-to-memcontrolc.patch
mm-memcg-cache-vmstat-data-in-percpu-memcg_stock_pcp.patch
mm-memcg-improve-refill_obj_stock-performance.patch
mm-memcg-optimize-user-context-object-stock-access.patch
