The current core of memcg charging is wild to say the least.
__mem_cgroup_try_charge which is in the center tries to be too clever
and it handles two independent cases
* when the memcg to be charged is known in advance
* when the given mm_struct is charged
The resulting callchains are quite complex:
memcg_charge_kmem(mm=NULL, memcg) mem_cgroup_newpage_charge(mm)
| | _________________________________________
mem_cgroup_cache_charge(current->mm)
| |/
|
| ______________________________ mem_cgroup_charge_common(mm, memcg=NULL)
|
|/
/
| /
| ____________________________ mem_cgroup_try_charge_swapin(mm, memcg=NULL) /
|/ | _________________________________________/
| |/
| | /* swap accounting
*/ /* no swap accounting */
| _____________________________ __mem_cgroup_try_charge_swapin(mm=NULL,
memcg) || (mm, memcg=NULL)
|/
| ____________________________ mem_cgroup_do_precharge(mm=NULL, memcg)
|/
__mem_cgroup_try_charge
mem_cgroup_do_charge
res_counter_charge
mem_cgroup_reclaim
mem_cgroup_wait_acct_move
mem_cgroup_oom
This patch splits __mem_cgroup_try_charge into two logical parts.
mem_cgroup_try_charge_mm which is responsible for charges for the given
mm_struct and it returns the charged memcg or NULL under OOM while
mem_cgroup_try_charge_memcg charges a known memcg and returns an error
code.
The only tricky part which remains is __mem_cgroup_try_charge_swapin
because it can return 0 if PageCgroupUsed is already set and then we do
not want to commit the charge. This is done with a magic combination of
memcg = NULL and ret = 0. So the function preserves its memcgp parameter
and sets the given memcg to NULL when it sees PageCgroupUsed
(__mem_cgroup_commit_charge_swapin then ignores such a commit).
Not only the code is easier to follow the change reduces the code size
too:
$ size mm/built-in.o.before
text data bss dec hex filename
457463 83162 49824 590449 90271 mm/built-in.o.before
$ size mm/built-in.o.after
text data bss dec hex filename
456794 83162 49824 589780 8ffd4 mm/built-in.o.after
Signed-off-by: Michal Hocko <[email protected]>
---
mm/memcontrol.c | 256 +++++++++++++++++++++++++++++---------------------------
1 file changed, 134 insertions(+), 122 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0ded63f1cc1e..509bb59f4744 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2581,7 +2581,7 @@ static int memcg_cpu_hotplug_callback(struct
notifier_block *nb,
}
-/* See __mem_cgroup_try_charge() for details */
+/* See mem_cgroup_do_charge() for details */
enum {
CHARGE_OK, /* success */
CHARGE_RETRY, /* need to retry but retry is not bad */
@@ -2655,37 +2655,68 @@ static int mem_cgroup_do_charge(struct mem_cgroup
*memcg, gfp_t gfp_mask,
}
/*
- * __mem_cgroup_try_charge() does
- * 1. detect memcg to be charged against from passed *mm and *ptr,
- * 2. update res_counter
- * 3. call memory reclaim if necessary.
+ * __mem_cgroup_try_charge_memcg - core of the memcg charging code. The caller
+ * keeps a css reference to the given memcg. We do not charge root_mem_cgroup.
+ * OOM is triggered only if allowed by the given oom parameter (except for
+ * __GFP_NOFAIL when it is ignored).
*
- * In some special case, if the task is fatal, fatal_signal_pending() or
- * has TIF_MEMDIE, this function returns -EINTR while writing root_mem_cgroup
- * to *ptr. There are two reasons for this. 1: fatal threads should quit as
soon
- * as possible without any hazards. 2: all pages should have a valid
- * pc->mem_cgroup. If mm is NULL and the caller doesn't pass a valid memcg
- * pointer, that is treated as a charge to root_mem_cgroup.
- *
- * So __mem_cgroup_try_charge() will return
- * 0 ... on success, filling *ptr with a valid memcg pointer.
- * -ENOMEM ... charge failure because of resource limits.
- * -EINTR ... if thread is fatal. *ptr is filled with root_mem_cgroup.
- *
- * Unlike the exported interface, an "oom" parameter is added. if oom==true,
- * the oom-killer can be invoked.
+ * Returns 0 on success, -ENOMEM when the given memcg is under OOM and -EINTR
+ * when the charge is bypassed (either when fatal signals are pending or
+ * __GFP_NOFAIL allocation cannot be charged).
*/
-static int __mem_cgroup_try_charge(struct mm_struct *mm,
- gfp_t gfp_mask,
+static int __mem_cgroup_try_charge_memcg(gfp_t gfp_mask,
unsigned int nr_pages,
- struct mem_cgroup **ptr,
+ struct mem_cgroup *memcg,
bool oom)
{
unsigned int batch = max(CHARGE_BATCH, nr_pages);
int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
- struct mem_cgroup *memcg = NULL;
int ret;
+ VM_BUG_ON(!memcg || memcg == root_mem_cgroup);
+
+ if (unlikely(task_in_memcg_oom(current)))
+ goto nomem;
+
+ if (gfp_mask & __GFP_NOFAIL)
+ oom = false;
+
+ do {
+ bool invoke_oom = oom && !nr_oom_retries;
+
+ /* If killed, bypass charge */
+ if (fatal_signal_pending(current))
+ goto bypass;
+
+ ret = mem_cgroup_do_charge(memcg, gfp_mask, batch,
+ nr_pages, invoke_oom);
+ switch (ret) {
+ case CHARGE_RETRY: /* not in OOM situation but retry */
+ batch = nr_pages;
+ break;
+ case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
+ goto nomem;
+ case CHARGE_NOMEM: /* OOM routine works */
+ if (!oom || invoke_oom)
+ goto nomem;
+ nr_oom_retries--;
+ break;
+ }
+ } while (ret != CHARGE_OK);
+
+ if (batch > nr_pages)
+ refill_stock(memcg, batch - nr_pages);
+
+ return 0;
+nomem:
+ if (!(gfp_mask & __GFP_NOFAIL))
+ return -ENOMEM;
+bypass:
+ return -EINTR;
+}
+
+static bool mem_cgroup_bypass_charge(void)
+{
/*
* Unlike gloval-vm's OOM-kill, we're not in memory shortage
* in system level. So, allow to go ahead dying process in addition to
@@ -2693,13 +2724,23 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
*/
if (unlikely(test_thread_flag(TIF_MEMDIE)
|| fatal_signal_pending(current)))
- goto bypass;
+ return true;
- if (unlikely(task_in_memcg_oom(current)))
- goto nomem;
+ return false;
+}
- if (gfp_mask & __GFP_NOFAIL)
- oom = false;
+/*
+ * Charges and returns memcg associated with the given mm (or root_mem_cgroup
+ * if mm is NULL). Returns NULL if memcg is under OOM.
+ */
+static struct mem_cgroup *mem_cgroup_try_charge_mm(struct mm_struct *mm,
+ gfp_t gfp_mask,
+ unsigned int nr_pages,
+ bool oom)
+{
+ struct mem_cgroup *memcg;
+ struct task_struct *p;
+ int ret;
/*
* We always charge the cgroup the mm_struct belongs to.
@@ -2707,18 +2748,12 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
* thread group leader migrates. It's possible that mm is not
* set, if so charge the root memcg (happens for pagecache usage).
*/
- if (!*ptr && !mm)
- *ptr = root_mem_cgroup;
-again:
- if (*ptr) { /* css should be a valid one */
- memcg = *ptr;
- if (mem_cgroup_is_root(memcg))
- goto done;
- if (consume_stock(memcg, nr_pages))
- goto done;
- css_get(&memcg->css);
- } else {
- struct task_struct *p;
+ if (!mm)
+ goto bypass;
+
+ do {
+ if (mem_cgroup_bypass_charge())
+ goto bypass;
rcu_read_lock();
p = rcu_dereference(mm->owner);
@@ -2733,11 +2768,9 @@ again:
* task-struct. So, mm->owner can be NULL.
*/
memcg = mem_cgroup_from_task(p);
- if (!memcg)
- memcg = root_mem_cgroup;
- if (mem_cgroup_is_root(memcg)) {
+ if (!memcg || mem_cgroup_is_root(memcg)) {
rcu_read_unlock();
- goto done;
+ goto bypass;
}
if (consume_stock(memcg, nr_pages)) {
/*
@@ -2752,59 +2785,37 @@ again:
goto done;
}
/* after here, we may be blocked. we need to get refcnt */
- if (!css_tryget(&memcg->css)) {
- rcu_read_unlock();
- goto again;
- }
- rcu_read_unlock();
- }
-
- do {
- bool invoke_oom = oom && !nr_oom_retries;
-
- /* If killed, bypass charge */
- if (fatal_signal_pending(current)) {
- css_put(&memcg->css);
- goto bypass;
- }
-
- ret = mem_cgroup_do_charge(memcg, gfp_mask, batch,
- nr_pages, invoke_oom);
- switch (ret) {
- case CHARGE_OK:
- break;
- case CHARGE_RETRY: /* not in OOM situation but retry */
- batch = nr_pages;
- css_put(&memcg->css);
- memcg = NULL;
- goto again;
- case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
- css_put(&memcg->css);
- goto nomem;
- case CHARGE_NOMEM: /* OOM routine works */
- if (!oom || invoke_oom) {
- css_put(&memcg->css);
- goto nomem;
- }
- nr_oom_retries--;
- break;
- }
- } while (ret != CHARGE_OK);
+ } while(!css_tryget(&memcg->css));
+ rcu_read_unlock();
- if (batch > nr_pages)
- refill_stock(memcg, batch - nr_pages);
+ ret = __mem_cgroup_try_charge_memcg(gfp_mask, nr_pages, memcg, oom);
css_put(&memcg->css);
+ if (ret == -EINTR)
+ goto bypass;
+ else if (ret == -ENOMEM)
+ memcg = NULL;
done:
- *ptr = memcg;
- return 0;
-nomem:
- if (!(gfp_mask & __GFP_NOFAIL)) {
- *ptr = NULL;
- return -ENOMEM;
- }
+ return memcg;
bypass:
- *ptr = root_mem_cgroup;
- return -EINTR;
+ return root_mem_cgroup;
+}
+
+/*
+ * charge the given memcg. The caller is has to hold a css reference for
+ * the given memcg.
+ */
+static int mem_cgroup_try_charge_memcg(gfp_t gfp_mask,
+ unsigned int nr_pages,
+ struct mem_cgroup *memcg,
+ bool oom)
+{
+ if (mem_cgroup_is_root(memcg) || mem_cgroup_bypass_charge())
+ return -EINTR;
+
+ if (consume_stock(memcg, nr_pages))
+ return 0;
+
+ return __mem_cgroup_try_charge_memcg(gfp_mask, nr_pages, memcg, oom);
}
/*
@@ -3002,21 +3013,19 @@ static int mem_cgroup_slabinfo_read(struct
cgroup_subsys_state *css,
static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
{
struct res_counter *fail_res;
- struct mem_cgroup *_memcg;
int ret = 0;
ret = res_counter_charge(&memcg->kmem, size, &fail_res);
if (ret)
return ret;
- _memcg = memcg;
- ret = __mem_cgroup_try_charge(NULL, gfp, size >> PAGE_SHIFT,
- &_memcg, oom_gfp_allowed(gfp));
+ ret = mem_cgroup_try_charge_memcg(gfp, size >> PAGE_SHIFT,
+ memcg, oom_gfp_allowed(gfp));
if (ret == -EINTR) {
/*
- * __mem_cgroup_try_charge() chosed to bypass to root due to
- * OOM kill or fatal signal. Since our only options are to
+ * __mem_cgroup_try_charge_memcg() chosed to bypass to root due
+ * to OOM kill or fatal signal. Since our only options are to
* either fail the allocation or charge it to this cgroup, do
* it as a temporary condition. But we can't fail. From a
* kmem/slab perspective, the cache has already been selected,
@@ -3025,7 +3034,7 @@ static int memcg_charge_kmem(struct mem_cgroup *memcg,
gfp_t gfp, u64 size)
*
* This condition will only trigger if the task entered
* memcg_charge_kmem in a sane state, but was OOM-killed during
- * __mem_cgroup_try_charge() above. Tasks that were already
+ * __mem_cgroup_try_charge_memcg() above. Tasks that were
already
* dying when the allocation triggers should have been already
* directed to the root cgroup in memcontrol.h
*/
@@ -3946,10 +3955,9 @@ out:
static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask, enum charge_type ctype)
{
- struct mem_cgroup *memcg = NULL;
+ struct mem_cgroup *memcg;
unsigned int nr_pages = 1;
bool oom = true;
- int ret;
if (PageTransHuge(page)) {
nr_pages <<= compound_order(page);
@@ -3961,9 +3969,9 @@ static int mem_cgroup_charge_common(struct page *page,
struct mm_struct *mm,
oom = false;
}
- ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
- if (ret == -ENOMEM)
- return ret;
+ memcg = mem_cgroup_try_charge_mm(mm, gfp_mask, nr_pages, oom);
+ if (!memcg)
+ return -ENOMEM;
__mem_cgroup_commit_charge(memcg, page, nr_pages, ctype, false);
return 0;
}
@@ -3987,8 +3995,7 @@ int mem_cgroup_newpage_charge(struct page *page,
* "commit()" or removed by "cancel()"
*/
static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
- struct page *page,
- gfp_t mask,
+ struct page *page, gfp_t mask,
struct mem_cgroup **memcgp)
{
struct mem_cgroup *memcg;
@@ -4002,31 +4009,36 @@ static int __mem_cgroup_try_charge_swapin(struct
mm_struct *mm,
* already charged pages, too. The USED bit is protected by
* the page lock, which serializes swap cache removal, which
* in turn serializes uncharging.
+ * Have to set memcg to NULL so that __mem_cgroup_commit_charge_swapin
+ * will ignore such a page.
*/
- if (PageCgroupUsed(pc))
+ if (PageCgroupUsed(pc)) {
+ *memcgp = NULL;
return 0;
+ }
if (!do_swap_account)
goto charge_cur_mm;
memcg = try_get_mem_cgroup_from_page(page);
if (!memcg)
goto charge_cur_mm;
*memcgp = memcg;
- ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
+ ret = mem_cgroup_try_charge_memcg(mask, 1, memcg, true);
css_put(&memcg->css);
- if (ret == -EINTR)
+ if (ret == -EINTR) {
+ *memcgp = root_mem_cgroup;
ret = 0;
+ }
return ret;
charge_cur_mm:
- ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
- if (ret == -EINTR)
- ret = 0;
- return ret;
+ *memcgp = mem_cgroup_try_charge_mm(mm, mask, 1, true);
+ if (!*memcgp)
+ return -ENOMEM;
+ return 0;
}
int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
gfp_t gfp_mask, struct mem_cgroup **memcgp)
{
- *memcgp = NULL;
if (mem_cgroup_disabled())
return 0;
/*
@@ -4036,13 +4048,14 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
struct page *page,
* there's also a KSM case which does need to charge the page.
*/
if (!PageSwapCache(page)) {
- int ret;
+ int ret = 0;
- ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
- if (ret == -EINTR)
- ret = 0;
+ *memcgp = mem_cgroup_try_charge_mm(mm, gfp_mask, 1, true);
+ if (!*memcgp)
+ ret = -ENOMEM;
return ret;
}
+
return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
}
@@ -4088,7 +4101,6 @@ void mem_cgroup_commit_charge_swapin(struct page *page,
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask)
{
- struct mem_cgroup *memcg = NULL;
enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
int ret;
@@ -4100,6 +4112,7 @@ int mem_cgroup_cache_charge(struct page *page, struct
mm_struct *mm,
if (!PageSwapCache(page))
ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
else { /* page is swapcache/shmem */
+ struct mem_cgroup *memcg;
ret = __mem_cgroup_try_charge_swapin(mm, page,
gfp_mask, &memcg);
if (!ret)
@@ -6442,8 +6455,7 @@ one_by_one:
batch_count = PRECHARGE_COUNT_AT_ONCE;
cond_resched();
}
- ret = __mem_cgroup_try_charge(NULL,
- GFP_KERNEL, 1, &memcg, false);
+ ret = mem_cgroup_try_charge_memcg(GFP_KERNEL, 1, memcg, false);
if (ret)
/* mem_cgroup_clear_mc() will do uncharge later */
return ret;
--
1.8.4.4
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