[RFC][PATCH 3/11] memcg: charge commit cancel protocol

KAMEZAWA Hiroyuki
2008-10-23T09:02:56Z

There is a small race in do_swap_page(). When the page swapped-in is charged,
the mapcount can be greater than 0. But, at the same time some process (shares
it ) call unmap and make mapcount 1->0 and the page is uncharged.

CPUA CPUB
mapcount == 1.
(1) charge if mapcount==0 zap_pte_range()
(2) mapcount 1 => 0.
(3) uncharge(). (success)
(4) set page'rmap()
mapcoint 0=>1

Then, this swap page's account is leaked.

For fixing this, I added a new interface.
- precharge
account to res_counter by PAGE_SIZE and try to free pages if necessary.
- commit
register page_cgroup and add to LRU if necessary.
- cancel
uncharge PAGE_SIZE because of do_swap_page failure.

CPUA
(1) charge (always)
(2) set page's rmap (mapcount > 0)
(3) commit charge was necessary or not after set_pte().

This protocol uses PCG_USED bit on page_cgroup for avoiding over accounting.
Usual mem_cgroup_charge_common() does precharge -> commit at a time.

And this patch also adds following function to clarify all charges.

- mem_cgroup_newpage_charge() ....replacement for mem_cgroup_charge()
called against newly allocated anon pages.

- mem_cgroup_charge_migrate_fixup()
called only from remove_migration_ptes().
we'll have to rewrite this later.(this patch just keeps old behavior)
This function will be removed by additional patch to make migration
clearer.

Good for clarify "what we does"

Then, we have 4 following charge points.
- newpage
- swapin
- add-to-cache.
- migration.

Changelog v7 -> v8
- handles that try_charge() sets NULL to *memcg.

Changelog v5 -> v7:
- added newpage_charge() and migrate_fixup().
- renamed functions for swap-in from "swap" to "swapin"
- add more precise description.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

include/linux/memcontrol.h | 35 +++++++++-
mm/memcontrol.c | 151 +++++++++++++++++++++++++++++++++++----------
mm/memory.c | 12 ++-
mm/migrate.c | 2
mm/swapfile.c | 6 +
5 files changed, 165 insertions(+), 41 deletions(-)

Index: mmotm-2.6.27+/include/linux/memcontrol.h
===================================================================
--- mmotm-2.6.27+.orig/include/linux/memcontrol.h
+++ mmotm-2.6.27+/include/linux/memcontrol.h
@@ -27,8 +27,17 @@ struct mm_struct;

#ifdef CONFIG_CGROUP_MEM_RES_CTLR

-extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
+extern int mem_cgroup_newpage_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask);
+extern int mem_cgroup_charge_migrate_fixup(struct page *page,
+ struct mm_struct *mm, gfp_t gfp_mask);
+/* for swap handling */
+extern int mem_cgroup_try_charge(struct mm_struct *mm,
+ gfp_t gfp_mask, struct mem_cgroup **ptr);
+extern void mem_cgroup_commit_charge_swapin(struct page *page,
+ struct mem_cgroup *ptr);
+extern void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr);
+
extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask);
extern void mem_cgroup_move_lists(struct page *page, enum lru_list lru);
@@ -71,7 +80,9 @@ extern long mem_cgroup_calc_reclaim(stru

#else /* CONFIG_CGROUP_MEM_RES_CTLR */
-static inline int mem_cgroup_charge(struct page *page,
+struct mem_cgroup;
+
+static inline int mem_cgroup_newpage_charge(struct page *page,
struct mm_struct *mm, gfp_t gfp_mask)
{
return 0;
@@ -83,6 +94,26 @@ static inline int mem_cgroup_cache_charg
return 0;
}

+static inline int mem_cgroup_charge_migrate_fixup(struct page *page,
+ struct mm_struct *mm, gfp_t gfp_mask)
+{
+ return 0;
+}
+
+static int mem_cgroup_try_charge(struct mm_struct *mm,
+ gfp_t gfp_mask, struct mem_cgroup **ptr)
+{
+ return 0;
+}
+
+static void mem_cgroup_commit_charge_swapin(struct page *page,
+ struct mem_cgroup *ptr)
+{
+}
+static void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *ptr)
+{
+}
+
static inline void mem_cgroup_uncharge_page(struct page *page)
{
}
Index: mmotm-2.6.27+/mm/memcontrol.c
===================================================================
--- mmotm-2.6.27+.orig/mm/memcontrol.c
+++ mmotm-2.6.27+/mm/memcontrol.c
@@ -467,35 +467,31 @@ unsigned long mem_cgroup_isolate_pages(u
return nr_taken;
}

-/*
- * Charge the memory controller for page usage.
- * Return
- * 0 if the charge was successful
- * < 0 if the cgroup is over its limit
+
+/**
+ * mem_cgroup_try_charge - get charge of PAGE_SIZE.
+ * @mm: an mm_struct which is charged against. (when *memcg is NULL)
+ * @gfp_mask: gfp_mask for reclaim.
+ * @memcg: a pointer to memory cgroup which is charged against.
+ *
+ * charge aginst memory cgroup pointed by *memcg. if *memcg == NULL, estimated
+ * memory cgroup from @mm is got and stored in *memcg.
+ *
+ * Retruns 0 if success. -ENOMEM at failure.
*/
-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)
+
+int mem_cgroup_try_charge(struct mm_struct *mm,
+ gfp_t gfp_mask, struct mem_cgroup **memcg)
{
struct mem_cgroup *mem;
- struct page_cgroup *pc;
- unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
- struct mem_cgroup_per_zone *mz;
- unsigned long flags;
-
- pc = lookup_page_cgroup(page);
- /* can happen at boot */
- if (unlikely(!pc))
- return 0;
- prefetchw(pc);
+ int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
/*
* We always charge the cgroup the mm_struct belongs to.
* The mm_struct's mem_cgroup changes on task migration if the
* thread group leader migrates. It's possible that mm is not
* set, if so charge the init_mm (happens for pagecache usage).
*/
-
- if (likely(!memcg)) {
+ if (likely(!*memcg)) {
rcu_read_lock();
mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
if (unlikely(!mem)) {
@@ -506,15 +502,17 @@ static int mem_cgroup_charge_common(stru
* For every charge from the cgroup, increment reference count
*/
css_get(&mem->css);
+ *memcg = mem;
rcu_read_unlock();
} else {
- mem = memcg;
- css_get(&memcg->css);
+ mem = *memcg;
+ css_get(&mem->css);
}

+
while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE))) {
if (!(gfp_mask & __GFP_WAIT))
- goto out;
+ goto nomem;

if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
continue;
@@ -531,18 +529,37 @@ static int mem_cgroup_charge_common(stru

if (!nr_retries--) {
mem_cgroup_out_of_memory(mem, gfp_mask);
- goto out;
+ goto nomem;
}
}
+ return 0;
+nomem:
+ css_put(&mem->css);
+ return -ENOMEM;
+}

+/*
+ * commit a charge got by mem_cgroup_try_charge() and makes page_cgroup to be
+ * USED state. If already USED, uncharge and return.
+ */
+
+static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
+ struct page_cgroup *pc,
+ enum charge_type ctype)
+{
+ struct mem_cgroup_per_zone *mz;
+ unsigned long flags;
+
+ /* try_charge() can return NULL to *memcg, taking care of it. */
+ if (!mem)
+ return;

lock_page_cgroup(pc);
if (unlikely(PageCgroupUsed(pc))) {
unlock_page_cgroup(pc);
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
-
- goto done;
+ return;
}
pc->mem_cgroup = mem;
/*
@@ -557,15 +574,39 @@ static int mem_cgroup_charge_common(stru
__mem_cgroup_add_list(mz, pc);
spin_unlock_irqrestore(&mz->lru_lock, flags);
unlock_page_cgroup(pc);
+}

-done:
+/*
+ * Charge the memory controller for page usage.
+ * Return
+ * 0 if the charge was successful
+ * < 0 if the cgroup is over its limit
+ */
+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)
+{
+ struct mem_cgroup *mem;
+ struct page_cgroup *pc;
+ int ret;
+
+ pc = lookup_page_cgroup(page);
+ /* can happen at boot */
+ if (unlikely(!pc))
+ return 0;
+ prefetchw(pc);
+
+ mem = memcg;
+ ret = mem_cgroup_try_charge(mm, gfp_mask, &mem);
+ if (ret)
+ return ret;
+
+ __mem_cgroup_commit_charge(mem, pc, ctype);
return 0;
-out:
- css_put(&mem->css);
- return -ENOMEM;
}

-int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
+int mem_cgroup_newpage_charge(struct page *page,
+ struct mm_struct *mm, gfp_t gfp_mask)
{
if (mem_cgroup_subsys.disabled)
return 0;
@@ -586,6 +627,34 @@ int mem_cgroup_charge(struct page *page,
MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
}

+/*
+ * same as mem_cgroup_newpage_charge(), now.
+ * But what we assume is different from newpage, and this is special case.
+ * treat this in special function. easy for maintainance.
+ */
+
+int mem_cgroup_charge_migrate_fixup(struct page *page,
+ struct mm_struct *mm, gfp_t gfp_mask)
+{
+ if (mem_cgroup_subsys.disabled)
+ return 0;
+
+ if (PageCompound(page))
+ return 0;
+
+ if (page_mapped(page) || (page->mapping && !PageAnon(page)))
+ return 0;
+
+ if (unlikely(!mm))
+ mm = &init_mm;
+
+ return mem_cgroup_charge_common(page, mm, gfp_mask,
+ MEM_CGROUP_CHARGE_TYPE_MAPPED, NULL);
+}
+
+
+
+
int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask)
{
@@ -628,6 +697,30 @@ int mem_cgroup_cache_charge(struct page
MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);
}

+
+void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
+{
+ struct page_cgroup *pc;
+
+ if (mem_cgroup_subsys.disabled)
+ return;
+ if (!ptr)
+ return;
+ pc = lookup_page_cgroup(page);
+ __mem_cgroup_commit_charge(ptr, pc, MEM_CGROUP_CHARGE_TYPE_MAPPED);
+}
+
+void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
+{
+ if (mem_cgroup_subsys.disabled)
+ return;
+ if (!mem)
+ return;
+ res_counter_uncharge(&mem->res, PAGE_SIZE);
+ css_put(&mem->css);
+}
+
+
/*
* uncharge if !page_mapped(page)
*/
Index: mmotm-2.6.27+/mm/memory.c
===================================================================
--- mmotm-2.6.27+.orig/mm/memory.c
+++ mmotm-2.6.27+/mm/memory.c
@@ -1889,7 +1889,7 @@ gotten:
cow_user_page(new_page, old_page, address, vma);
__SetPageUptodate(new_page);

- if (mem_cgroup_charge(new_page, mm, GFP_KERNEL))
+ if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
goto oom_free_new;

/*
@@ -2285,6 +2285,7 @@ static int do_swap_page(struct mm_struct
struct page *page;
swp_entry_t entry;
pte_t pte;
+ struct mem_cgroup *ptr = NULL;
int ret = 0;

if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
@@ -2323,7 +2324,7 @@ static int do_swap_page(struct mm_struct
lock_page(page);
delayacct_clear_flag(DELAYACCT_PF_SWAPIN);

- if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
+ if (mem_cgroup_try_charge(mm, GFP_KERNEL, &ptr) == -ENOMEM) {
ret = VM_FAULT_OOM;
unlock_page(page);
goto out;
@@ -2353,6 +2354,7 @@ static int do_swap_page(struct mm_struct
flush_icache_page(vma, page);
set_pte_at(mm, address, page_table, pte);
page_add_anon_rmap(page, vma, address);
+ mem_cgroup_commit_charge_swapin(page, ptr);

swap_free(entry);
if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
@@ -2373,7 +2375,7 @@ unlock:
out:
return ret;
out_nomap:
- mem_cgroup_uncharge_page(page);
+ mem_cgroup_cancel_charge_swapin(ptr);
pte_unmap_unlock(page_table, ptl);
unlock_page(page);
page_cache_release(page);
@@ -2403,7 +2405,7 @@ static int do_anonymous_page(struct mm_s
goto oom;
__SetPageUptodate(page);

- if (mem_cgroup_charge(page, mm, GFP_KERNEL))
+ if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))
goto oom_free_page;

entry = mk_pte(page, vma->vm_page_prot);
@@ -2496,7 +2498,7 @@ static int __do_fault(struct mm_struct *
ret = VM_FAULT_OOM;
goto out;
}
- if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
+ if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
ret = VM_FAULT_OOM;
page_cache_release(page);
goto out;
Index: mmotm-2.6.27+/mm/migrate.c
===================================================================
--- mmotm-2.6.27+.orig/mm/migrate.c
+++ mmotm-2.6.27+/mm/migrate.c
@@ -133,7 +133,7 @@ static void remove_migration_pte(struct
* be reliable, and this charge can actually fail: oh well, we don't
* make the situation any worse by proceeding as if it had succeeded.
*/
- mem_cgroup_charge(new, mm, GFP_ATOMIC);
+ mem_cgroup_charge_migrate_fixup(new, mm, GFP_ATOMIC);

get_page(new);
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
Index: mmotm-2.6.27+/mm/swapfile.c
===================================================================
--- mmotm-2.6.27+.orig/mm/swapfile.c
+++ mmotm-2.6.27+/mm/swapfile.c
@@ -530,17 +530,18 @@ unsigned int count_swap_pages(int type,
static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, swp_entry_t entry, struct page *page)
{
+ struct mem_cgroup *ptr = NULL;
spinlock_t *ptl;
pte_t *pte;
int ret = 1;

- if (mem_cgroup_charge(page, vma->vm_mm, GFP_KERNEL))
+ if (mem_cgroup_try_charge(vma->vm_mm, GFP_KERNEL, &ptr))
ret = -ENOMEM;

pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
if (ret > 0)
- mem_cgroup_uncharge_page(page);
+ mem_cgroup_cancel_charge_swapin(ptr);
ret = 0;
goto out;
}
@@ -550,6 +551,7 @@ static int unuse_pte(struct vm_area_stru
set_pte_at(vma->vm_mm, addr, pte,
pte_mkold(mk_pte(page, vma->vm_page_prot)));
page_add_anon_rmap(page, vma, addr);
+ mem_cgroup_commit_charge_swapin(page, ptr);
swap_free(entry);
/*
* Move the page to the active list so it is not