When handing slab objects, we use obj_cgroup_[un]charge() for
(un)charging and mod_objcg_state() to account NR_SLAB_[UN]RECLAIMABLE_B.
All these operations use the percpu stock for performance. However with
the calls being separate, the stock_lock is taken twice in each case.
By refactoring the code, we can turn mod_objcg_state() into
__account_obj_stock() which is called on a stock that's already locked
and validated. On the charging side we can call this function from
consume_obj_stock() when it succeeds, and refill_obj_stock() in the
fallback. We just expand parameters of these functions as necessary.
The uncharge side from __memcg_slab_free_hook() is just the call to
refill_obj_stock().
Other callers of obj_cgroup_[un]charge() (i.e. not slab) simply pass the
extra parameters as NULL/zeroes to skip the __account_obj_stock()
operation.
In __memcg_slab_post_alloc_hook() we now charge each object separately,
but that's not a problem as we did call mod_objcg_state() for each
object separately, and most allocations are non-bulk anyway. This
could be improved by batching all operations until slab_pgdat(slab)
changes.
Some preliminary benchmarking with a kfree(kmalloc()) loop of 10M
iterations with/without __GFP_ACCOUNT:
Before the patch:
kmalloc/kfree !memcg: 581390144 cycles
kmalloc/kfree memcg: 783689984 cycles
After the patch:
kmalloc/kfree memcg: 658723808 cycles
More than half of the overhead of __GFP_ACCOUNT relative to
non-accounted case seems eliminated.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/memcontrol.c | 77 +++++++++++++++++++++++++++++--------------------
1 file changed, 46 insertions(+), 31 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dfe9c2eb7816..553eb1d7250a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2753,25 +2753,17 @@ static void replace_stock_objcg(struct memcg_stock_pcp *stock,
WRITE_ONCE(stock->cached_objcg, objcg);
}
-static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
- enum node_stat_item idx, int nr)
+static void __account_obj_stock(struct obj_cgroup *objcg,
+ struct memcg_stock_pcp *stock, int nr,
+ struct pglist_data *pgdat, enum node_stat_item idx)
{
- struct memcg_stock_pcp *stock;
- unsigned long flags;
int *bytes;
- localtry_lock_irqsave(&memcg_stock.stock_lock, 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
- * changes.
+ * accumulating over a page of vmstat data or when pgdat changes.
*/
- if (READ_ONCE(stock->cached_objcg) != objcg) {
- replace_stock_objcg(stock, objcg);
- stock->cached_pgdat = pgdat;
- } else if (stock->cached_pgdat != pgdat) {
+ if (stock->cached_pgdat != pgdat) {
/* Flush the existing cached vmstat data */
struct pglist_data *oldpg = stock->cached_pgdat;
@@ -2808,11 +2800,10 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
}
if (nr)
__mod_objcg_mlstate(objcg, pgdat, idx, nr);
-
- localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
}
-static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
+static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
+ struct pglist_data *pgdat, enum node_stat_item idx)
{
struct memcg_stock_pcp *stock;
unsigned long flags;
@@ -2824,6 +2815,9 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
stock->nr_bytes -= nr_bytes;
ret = true;
+
+ if (pgdat)
+ __account_obj_stock(objcg, stock, nr_bytes, pgdat, idx);
}
localtry_unlock_irqrestore(&memcg_stock.stock_lock, flags);
@@ -2908,7 +2902,8 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
}
static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
- bool allow_uncharge)
+ bool allow_uncharge, int nr_acct, struct pglist_data *pgdat,
+ enum node_stat_item idx)
{
struct memcg_stock_pcp *stock;
unsigned long flags;
@@ -2923,6 +2918,9 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
}
stock->nr_bytes += nr_bytes;
+ if (pgdat)
+ __account_obj_stock(objcg, stock, nr_acct, pgdat, idx);
+
if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) {
nr_pages = stock->nr_bytes >> PAGE_SHIFT;
stock->nr_bytes &= (PAGE_SIZE - 1);
@@ -2934,12 +2932,13 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
obj_cgroup_uncharge_pages(objcg, nr_pages);
}
-int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
+static int obj_cgroup_charge_account(struct obj_cgroup *objcg, gfp_t gfp, size_t size,
+ struct pglist_data *pgdat, enum node_stat_item idx)
{
unsigned int nr_pages, nr_bytes;
int ret;
- if (consume_obj_stock(objcg, size))
+ if (likely(consume_obj_stock(objcg, size, pgdat, idx)))
return 0;
/*
@@ -2972,15 +2971,21 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
nr_pages += 1;
ret = obj_cgroup_charge_pages(objcg, gfp, nr_pages);
- if (!ret && nr_bytes)
- refill_obj_stock(objcg, PAGE_SIZE - nr_bytes, false);
+ if (!ret && (nr_bytes || pgdat))
+ refill_obj_stock(objcg, nr_bytes ? PAGE_SIZE - nr_bytes : 0,
+ false, size, pgdat, idx);
return ret;
}
+int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size)
+{
+ return obj_cgroup_charge_account(objcg, gfp, size, NULL, 0);
+}
+
void obj_cgroup_uncharge(struct obj_cgroup *objcg, size_t size)
{
- refill_obj_stock(objcg, size, true);
+ refill_obj_stock(objcg, size, true, 0, NULL, 0);
}
static inline size_t obj_full_size(struct kmem_cache *s)
@@ -3032,23 +3037,32 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
return false;
}
- if (obj_cgroup_charge(objcg, flags, size * obj_full_size(s)))
- return false;
-
for (i = 0; i < size; i++) {
slab = virt_to_slab(p[i]);
if (!slab_obj_exts(slab) &&
alloc_slab_obj_exts(slab, s, flags, false)) {
- obj_cgroup_uncharge(objcg, obj_full_size(s));
continue;
}
+ /*
+ * if we fail and size is 1, memcg_alloc_abort_single() will
+ * just free the object, which is ok as we have not assigned
+ * objcg to its obj_ext yet
+ *
+ * for larger sizes, kmem_cache_free_bulk() will uncharge
+ * any objects that were already charged and obj_ext assigned
+ *
+ * TODO: we could batch this until slab_pgdat(slab) changes
+ * between iterations, with a more complicated undo
+ */
+ if (obj_cgroup_charge_account(objcg, flags, obj_full_size(s),
+ slab_pgdat(slab), cache_vmstat_idx(s)))
+ return false;
+
off = obj_to_index(s, slab, p[i]);
obj_cgroup_get(objcg);
slab_obj_exts(slab)[off].objcg = objcg;
- mod_objcg_state(objcg, slab_pgdat(slab),
- cache_vmstat_idx(s), obj_full_size(s));
}
return true;
@@ -3057,6 +3071,8 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
void **p, int objects, struct slabobj_ext *obj_exts)
{
+ size_t obj_size = obj_full_size(s);
+
for (int i = 0; i < objects; i++) {
struct obj_cgroup *objcg;
unsigned int off;
@@ -3067,9 +3083,8 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
continue;
obj_exts[off].objcg = NULL;
- obj_cgroup_uncharge(objcg, obj_full_size(s));
- mod_objcg_state(objcg, slab_pgdat(slab), cache_vmstat_idx(s),
- -obj_full_size(s));
+ refill_obj_stock(objcg, obj_size, true, -obj_size,
+ slab_pgdat(slab), cache_vmstat_idx(s));
obj_cgroup_put(objcg);
}
}
--
2.48.1
