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mm: memcontrol: use root_mem_cgroup res_counter
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Due to an old optimization to keep expensive res_counter changes at a
minimum, the root_mem_cgroup res_counter is never charged; there is no
limit at that level anyway, and any statistics can be generated on
demand by summing up the counters of all other cgroups.

However, with per-cpu charge caches, res_counter operations do not even
show up in profiles anymore, so this optimization is no longer
necessary.

Remove it to simplify the code.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Johannes Weiner authored and Linus Torvalds committed Aug 7, 2014
1 parent 692e7c4 commit 05b8430
Showing 1 changed file with 44 additions and 108 deletions.
152 changes: 44 additions & 108 deletions mm/memcontrol.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2570,9 +2570,8 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
unsigned long nr_reclaimed;
unsigned long flags = 0;
unsigned long long size;
int ret = 0;

if (mem_cgroup_is_root(memcg))
goto done;
retry:
if (consume_stock(memcg, nr_pages))
goto done;
Expand Down Expand Up @@ -2650,13 +2649,15 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
if (!(gfp_mask & __GFP_NOFAIL))
return -ENOMEM;
bypass:
return -EINTR;
memcg = root_mem_cgroup;
ret = -EINTR;
goto retry;

done_restock:
if (batch > nr_pages)
refill_stock(memcg, batch - nr_pages);
done:
return 0;
return ret;
}

/**
Expand Down Expand Up @@ -2695,13 +2696,11 @@ static struct mem_cgroup *mem_cgroup_try_charge_mm(struct mm_struct *mm,
static void __mem_cgroup_cancel_charge(struct mem_cgroup *memcg,
unsigned int nr_pages)
{
if (!mem_cgroup_is_root(memcg)) {
unsigned long bytes = nr_pages * PAGE_SIZE;
unsigned long bytes = nr_pages * PAGE_SIZE;

res_counter_uncharge(&memcg->res, bytes);
if (do_swap_account)
res_counter_uncharge(&memcg->memsw, bytes);
}
res_counter_uncharge(&memcg->res, bytes);
if (do_swap_account)
res_counter_uncharge(&memcg->memsw, bytes);
}

/*
Expand All @@ -2713,9 +2712,6 @@ static void __mem_cgroup_cancel_local_charge(struct mem_cgroup *memcg,
{
unsigned long bytes = nr_pages * PAGE_SIZE;

if (mem_cgroup_is_root(memcg))
return;

res_counter_uncharge_until(&memcg->res, memcg->res.parent, bytes);
if (do_swap_account)
res_counter_uncharge_until(&memcg->memsw,
Expand Down Expand Up @@ -3943,7 +3939,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype,
* replacement page, so leave it alone when phasing out the
* page that is unused after the migration.
*/
if (!end_migration && !mem_cgroup_is_root(memcg))
if (!end_migration)
mem_cgroup_do_uncharge(memcg, nr_pages, ctype);

return memcg;
Expand Down Expand Up @@ -4076,8 +4072,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
* We uncharge this because swap is freed. This memcg can
* be obsolete one. We avoid calling css_tryget_online().
*/
if (!mem_cgroup_is_root(memcg))
res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
mem_cgroup_swap_statistics(memcg, false);
css_put(&memcg->css);
}
Expand Down Expand Up @@ -4767,78 +4762,24 @@ static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
return retval;
}


static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *memcg,
enum mem_cgroup_stat_index idx)
{
struct mem_cgroup *iter;
long val = 0;

/* Per-cpu values can be negative, use a signed accumulator */
for_each_mem_cgroup_tree(iter, memcg)
val += mem_cgroup_read_stat(iter, idx);

if (val < 0) /* race ? */
val = 0;
return val;
}

static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
{
u64 val;

if (!mem_cgroup_is_root(memcg)) {
if (!swap)
return res_counter_read_u64(&memcg->res, RES_USAGE);
else
return res_counter_read_u64(&memcg->memsw, RES_USAGE);
}

/*
* Transparent hugepages are still accounted for in MEM_CGROUP_STAT_RSS
* as well as in MEM_CGROUP_STAT_RSS_HUGE.
*/
val = mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_CACHE);
val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_RSS);

if (swap)
val += mem_cgroup_recursive_stat(memcg, MEM_CGROUP_STAT_SWAP);

return val << PAGE_SHIFT;
}

static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
struct cftype *cft)
struct cftype *cft)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
u64 val;
int name;
enum res_type type;

type = MEMFILE_TYPE(cft->private);
name = MEMFILE_ATTR(cft->private);
enum res_type type = MEMFILE_TYPE(cft->private);
int name = MEMFILE_ATTR(cft->private);

switch (type) {
case _MEM:
if (name == RES_USAGE)
val = mem_cgroup_usage(memcg, false);
else
val = res_counter_read_u64(&memcg->res, name);
break;
return res_counter_read_u64(&memcg->res, name);
case _MEMSWAP:
if (name == RES_USAGE)
val = mem_cgroup_usage(memcg, true);
else
val = res_counter_read_u64(&memcg->memsw, name);
break;
return res_counter_read_u64(&memcg->memsw, name);
case _KMEM:
val = res_counter_read_u64(&memcg->kmem, name);
return res_counter_read_u64(&memcg->kmem, name);
break;
default:
BUG();
}

return val;
}

#ifdef CONFIG_MEMCG_KMEM
Expand Down Expand Up @@ -5300,7 +5241,10 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
if (!t)
goto unlock;

usage = mem_cgroup_usage(memcg, swap);
if (!swap)
usage = res_counter_read_u64(&memcg->res, RES_USAGE);
else
usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);

/*
* current_threshold points to threshold just below or equal to usage.
Expand Down Expand Up @@ -5396,15 +5340,15 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,

mutex_lock(&memcg->thresholds_lock);

if (type == _MEM)
if (type == _MEM) {
thresholds = &memcg->thresholds;
else if (type == _MEMSWAP)
usage = res_counter_read_u64(&memcg->res, RES_USAGE);
} else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
else
usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
} else
BUG();

usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

/* Check if a threshold crossed before adding a new one */
if (thresholds->primary)
__mem_cgroup_threshold(memcg, type == _MEMSWAP);
Expand Down Expand Up @@ -5484,18 +5428,19 @@ static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
int i, j, size;

mutex_lock(&memcg->thresholds_lock);
if (type == _MEM)

if (type == _MEM) {
thresholds = &memcg->thresholds;
else if (type == _MEMSWAP)
usage = res_counter_read_u64(&memcg->res, RES_USAGE);
} else if (type == _MEMSWAP) {
thresholds = &memcg->memsw_thresholds;
else
usage = res_counter_read_u64(&memcg->memsw, RES_USAGE);
} else
BUG();

if (!thresholds->primary)
goto unlock;

usage = mem_cgroup_usage(memcg, type == _MEMSWAP);

/* Check if a threshold crossed before removing */
__mem_cgroup_threshold(memcg, type == _MEMSWAP);

Expand Down Expand Up @@ -6249,9 +6194,9 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
* core guarantees its existence.
*/
} else {
res_counter_init(&memcg->res, NULL);
res_counter_init(&memcg->memsw, NULL);
res_counter_init(&memcg->kmem, NULL);
res_counter_init(&memcg->res, &root_mem_cgroup->res);
res_counter_init(&memcg->memsw, &root_mem_cgroup->memsw);
res_counter_init(&memcg->kmem, &root_mem_cgroup->kmem);
/*
* Deeper hierachy with use_hierarchy == false doesn't make
* much sense so let cgroup subsystem know about this
Expand Down Expand Up @@ -6387,13 +6332,7 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
/* Handlers for move charge at task migration. */
static int mem_cgroup_do_precharge(unsigned long count)
{
int ret = 0;

if (mem_cgroup_is_root(mc.to)) {
mc.precharge += count;
/* we don't need css_get for root */
return ret;
}
int ret;

/* Try a single bulk charge without reclaim first */
ret = mem_cgroup_try_charge(mc.to, GFP_KERNEL & ~__GFP_WAIT, count);
Expand Down Expand Up @@ -6700,21 +6639,18 @@ static void __mem_cgroup_clear_mc(void)
/* we must fixup refcnts and charges */
if (mc.moved_swap) {
/* uncharge swap account from the old cgroup */
if (!mem_cgroup_is_root(mc.from))
res_counter_uncharge(&mc.from->memsw,
PAGE_SIZE * mc.moved_swap);
res_counter_uncharge(&mc.from->memsw,
PAGE_SIZE * mc.moved_swap);

for (i = 0; i < mc.moved_swap; i++)
css_put(&mc.from->css);

if (!mem_cgroup_is_root(mc.to)) {
/*
* we charged both to->res and to->memsw, so we should
* uncharge to->res.
*/
res_counter_uncharge(&mc.to->res,
PAGE_SIZE * mc.moved_swap);
}
/*
* we charged both to->res and to->memsw, so we should
* uncharge to->res.
*/
res_counter_uncharge(&mc.to->res,
PAGE_SIZE * mc.moved_swap);
/* we've already done css_get(mc.to) */
mc.moved_swap = 0;
}
Expand Down

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