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memcg: combine slab obj stock charging and accounting

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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.

Link: https://lkml.kernel.org/r/20250404013913.1663035-9-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2025-04-03 18:39:12 -07:00 committed by Andrew Morton
parent 42a1910cfd
commit bc730030f9
1 changed files with 46 additions and 31 deletions
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77
mm/memcontrol.c
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@ -2774,25 +2774,17 @@ 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;
local_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;
@ -2829,11 +2821,10 @@ static void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
}
if (nr)
__mod_objcg_mlstate(objcg, pgdat, idx, nr);
local_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;
@ -2845,6 +2836,9 @@ 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);
}
local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
@ -2929,7 +2923,8 @@ 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;
@ -2944,6 +2939,9 @@ 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);
@ -2955,12 +2953,13 @@ 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;
/*
@ -2993,15 +2992,21 @@ 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)
@ -3053,23 +3058,32 @@ 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;
@ -3078,6 +3092,8 @@ 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;
@ -3088,9 +3104,8 @@ 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);
}
}