On Tue 08-02-22 09:58:27, Shakeel Butt wrote:
[...]
> commit 559271146efc0 is a part of patch series "mm/memcg: Reduce
> kmemcache memory accounting overhead". For perf numbers you can see
> the cover letter in the commit fdbcb2a6d677 ("mm/memcg: move
> mod_objcg_state() to memcontrol.c").
Thanks for the pointer! This helped because I couldn't follow the
original series[1].
I definitely do not want to dispute the whole series. It is this
particular patch which makes further changes much more complex AFAICS
and the cost/benefit should be re-evaluated IMHO. Microbenchmarks are a
nice indecation but in this case we should be more re-evaluate. The
complexity has increased even more for RT requirements.
[1] It would be great if those patch specific benchmarks were in the
specific patch next time. This would make it much more easier to track.
Just as an exercise I have tried to revert 559271146efc0. It needs some
tweaking (on top of Linus tree) and I hope I got everything right.
Sebastian does this help for the RT case?
---
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 09d342c7cbd0..4b1572ae990d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2085,23 +2085,17 @@ void unlock_page_memcg(struct page *page)
folio_memcg_unlock(page_folio(page));
}
-struct obj_stock {
+struct memcg_stock_pcp {
+ struct mem_cgroup *cached; /* this never be root cgroup */
+ unsigned int nr_pages;
+
#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;
@@ -2111,12 +2105,12 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
static DEFINE_MUTEX(percpu_charge_mutex);
#ifdef CONFIG_MEMCG_KMEM
-static void drain_obj_stock(struct obj_stock *stock);
+static void drain_obj_stock(struct memcg_stock_pcp *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 obj_stock *stock)
+static inline void drain_obj_stock(struct memcg_stock_pcp *stock)
{
}
static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
@@ -2193,9 +2187,7 @@ static void drain_local_stock(struct work_struct *dummy)
local_irq_save(flags);
stock = this_cpu_ptr(&memcg_stock);
- drain_obj_stock(&stock->irq_obj);
- if (in_task())
- drain_obj_stock(&stock->task_obj);
+ drain_obj_stock(stock);
drain_stock(stock);
clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
@@ -2770,41 +2762,6 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg)
*/
#define OBJCGS_CLEAR_MASK (__GFP_DMA | __GFP_RECLAIMABLE | __GFP_ACCOUNT)
-/*
- * 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())) {
- *pflags = 0UL;
- preempt_disable();
- stock = this_cpu_ptr(&memcg_stock);
- return &stock->task_obj;
- }
-
- 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);
-}
-
/*
* mod_objcg_mlstate() may be called with irq enabled, so
* mod_memcg_lruvec_state() should be used.
@@ -3075,10 +3032,13 @@ void __memcg_kmem_uncharge_page(struct page *page, int order)
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
@@ -3129,26 +3089,29 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
if (nr)
mod_objcg_mlstate(objcg, pgdat, idx, nr);
- put_obj_stock(flags);
+ local_irq_restore(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;
}
- put_obj_stock(flags);
+ local_irq_restore(flags);
return ret;
}
-static void drain_obj_stock(struct obj_stock *stock)
+static void drain_obj_stock(struct memcg_stock_pcp *stock)
{
struct obj_cgroup *old = stock->cached_objcg;
@@ -3204,13 +3167,8 @@ static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
{
struct mem_cgroup *memcg;
- 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 (stock->cached_objcg) {
+ memcg = obj_cgroup_memcg(stock->cached_objcg);
if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
return true;
}
@@ -3221,10 +3179,13 @@ 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)
{
+ 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);
@@ -3240,7 +3201,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
stock->nr_bytes &= (PAGE_SIZE - 1);
}
- put_obj_stock(flags);
+ local_irq_restore(flags);
if (nr_pages)
obj_cgroup_uncharge_pages(objcg, nr_pages);
@@ -6821,7 +6782,6 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
long nr_pages;
struct mem_cgroup *memcg;
struct obj_cgroup *objcg;
- bool use_objcg = folio_memcg_kmem(folio);
VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
@@ -6830,7 +6790,7 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
* folio memcg or objcg at this point, we have fully
* exclusive access to the folio.
*/
- if (use_objcg) {
+ if (folio_memcg_kmem(folio)) {
objcg = __folio_objcg(folio);
/*
* This get matches the put at the end of the function and
@@ -6858,7 +6818,7 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
nr_pages = folio_nr_pages(folio);
- if (use_objcg) {
+ if (folio_memcg_kmem(folio)) {
ug->nr_memory += nr_pages;
ug->nr_kmem += nr_pages;
--
Michal Hocko
SUSE Labs
