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mm/memcg: revert ("mm/memcg: optimize user context object stock access")

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Patch series "mm/memcg: Address PREEMPT_RT problems instead of disabling it", v5.

This series aims to address the memcg related problem on PREEMPT_RT.

I tested them on CONFIG_PREEMPT and CONFIG_PREEMPT_RT with the
tools/testing/selftests/cgroup/* tests and I haven't observed any
regressions (other than the lockdep report that is already there).

This patch (of 6):

The optimisation is based on a micro benchmark where local_irq_save() is
more expensive than a preempt_disable().  There is no evidence that it
is visible in a real-world workload and there are CPUs where the
opposite is true (local_irq_save() is cheaper than preempt_disable()).

Based on micro benchmarks, the optimisation makes sense on PREEMPT_NONE
where preempt_disable() is optimized away.  There is no improvement with
PREEMPT_DYNAMIC since the preemption counter is always available.

The optimization makes also the PREEMPT_RT integration more complicated
since most of the assumption are not true on PREEMPT_RT.

Revert the optimisation since it complicates the PREEMPT_RT integration
and the improvement is hardly visible.

[bigeasy@linutronix.de: patch body around Michal's diff]

Link: https://lkml.kernel.org/r/20220226204144.1008339-1-bigeasy@linutronix.de
Link: https://lore.kernel.org/all/YgOGkXXCrD%2F1k+p4@dhcp22.suse.cz
Link: https://lkml.kernel.org/r/YdX+INO9gQje6d0S@linutronix.de
Link: https://lkml.kernel.org/r/20220226204144.1008339-2-bigeasy@linutronix.de
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Waiman Long <longman@redhat.com>
Cc: kernel test robot <oliver.sang@intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2022-03-22 14:40:35 -07:00 committed by Linus Torvalds
parent 460a79e188
commit fead2b8697
1 changed files with 27 additions and 67 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

94
mm/memcontrol.c
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@ -2078,23 +2078,17 @@ 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;
@ -2104,13 +2098,13 @@ 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);
static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages);
#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,
@ -2190,9 +2184,7 @@ 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);
@ -2767,41 +2759,6 @@ retry:
*/
#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.
@ -3082,10 +3039,13 @@ 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
@ -3136,26 +3096,29 @@ 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;
@ -3211,13 +3174,8 @@ 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;
}
@ -3228,10 +3186,13 @@ 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);
@ -3247,7 +3208,7 @@ 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);
@ -6826,7 +6787,6 @@ 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);
@ -6835,7 +6795,7 @@ 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
@ -6863,7 +6823,7 @@ 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;