memcg: simplify LRU handling by new rule
Now, at LRU handling, memory cgroup needs to do complicated works to see
valid pc->mem_cgroup, which may be overwritten.
This patch is for relaxing the protocol. This patch guarantees
- when pc->mem_cgroup is overwritten, page must not be on LRU.
By this, LRU routine can believe pc->mem_cgroup and don't need to check
bits on pc->flags. This new rule may adds small overheads to swapin. But
in most case, lru handling gets faster.
After this patch, PCG_ACCT_LRU bit is obsolete and removed.
[akpm@linux-foundation.org: remove unneeded VM_BUG_ON(), restore hannes's christmas tree]
[akpm@linux-foundation.org: clean up code comment]
[hughd@google.com: fix NULL mem_cgroup_try_charge]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c74102d..ff051ee 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1040,30 +1040,7 @@
return &zone->lruvec;
pc = lookup_page_cgroup(page);
- VM_BUG_ON(PageCgroupAcctLRU(pc));
- /*
- * putback: charge:
- * SetPageLRU SetPageCgroupUsed
- * smp_mb smp_mb
- * PageCgroupUsed && add to memcg LRU PageLRU && add to memcg LRU
- *
- * Ensure that one of the two sides adds the page to the memcg
- * LRU during a race.
- */
- smp_mb();
- /*
- * If the page is uncharged, it may be freed soon, but it
- * could also be swap cache (readahead, swapoff) that needs to
- * be reclaimable in the future. root_mem_cgroup will babysit
- * it for the time being.
- */
- if (PageCgroupUsed(pc)) {
- /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
- smp_rmb();
- memcg = pc->mem_cgroup;
- SetPageCgroupAcctLRU(pc);
- } else
- memcg = root_mem_cgroup;
+ memcg = pc->mem_cgroup;
mz = page_cgroup_zoneinfo(memcg, page);
/* compound_order() is stabilized through lru_lock */
MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
@@ -1090,18 +1067,8 @@
return;
pc = lookup_page_cgroup(page);
- /*
- * root_mem_cgroup babysits uncharged LRU pages, but
- * PageCgroupUsed is cleared when the page is about to get
- * freed. PageCgroupAcctLRU remembers whether the
- * LRU-accounting happened against pc->mem_cgroup or
- * root_mem_cgroup.
- */
- if (TestClearPageCgroupAcctLRU(pc)) {
- VM_BUG_ON(!pc->mem_cgroup);
- memcg = pc->mem_cgroup;
- } else
- memcg = root_mem_cgroup;
+ memcg = pc->mem_cgroup;
+ VM_BUG_ON(!memcg);
mz = page_cgroup_zoneinfo(memcg, page);
/* huge page split is done under lru_lock. so, we have no races. */
MEM_CGROUP_ZSTAT(mz, lru) -= 1 << compound_order(page);
@@ -2217,8 +2184,25 @@
}
/*
- * Unlike exported interface, "oom" parameter is added. if oom==true,
- * oom-killer can be invoked.
+ * __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.
+ *
+ * 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.
*/
static int __mem_cgroup_try_charge(struct mm_struct *mm,
gfp_t gfp_mask,
@@ -2247,7 +2231,7 @@
* set, if so charge the init_mm (happens for pagecache usage).
*/
if (!*ptr && !mm)
- goto bypass;
+ *ptr = root_mem_cgroup;
again:
if (*ptr) { /* css should be a valid one */
memcg = *ptr;
@@ -2273,7 +2257,9 @@
* task-struct. So, mm->owner can be NULL.
*/
memcg = mem_cgroup_from_task(p);
- if (!memcg || mem_cgroup_is_root(memcg)) {
+ if (!memcg)
+ memcg = root_mem_cgroup;
+ if (mem_cgroup_is_root(memcg)) {
rcu_read_unlock();
goto done;
}
@@ -2348,8 +2334,8 @@
*ptr = NULL;
return -ENOMEM;
bypass:
- *ptr = NULL;
- return 0;
+ *ptr = root_mem_cgroup;
+ return -EINTR;
}
/*
@@ -2457,6 +2443,7 @@
mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), nr_pages);
unlock_page_cgroup(pc);
+ WARN_ON_ONCE(PageLRU(page));
/*
* "charge_statistics" updated event counter. Then, check it.
* Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
@@ -2468,7 +2455,7 @@
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (1 << PCG_MOVE_LOCK) |\
- (1 << PCG_ACCT_LRU) | (1 << PCG_MIGRATION))
+ (1 << PCG_MIGRATION))
/*
* Because tail pages are not marked as "used", set it. We're under
* zone->lru_lock, 'splitting on pmd' and compound_lock.
@@ -2478,7 +2465,9 @@
void mem_cgroup_split_huge_fixup(struct page *head)
{
struct page_cgroup *head_pc = lookup_page_cgroup(head);
+ struct mem_cgroup_per_zone *mz;
struct page_cgroup *pc;
+ enum lru_list lru;
int i;
if (mem_cgroup_disabled())
@@ -2487,23 +2476,15 @@
pc = head_pc + i;
pc->mem_cgroup = head_pc->mem_cgroup;
smp_wmb();/* see __commit_charge() */
- /*
- * LRU flags cannot be copied because we need to add tail
- * page to LRU by generic call and our hooks will be called.
- */
pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
}
-
- if (PageCgroupAcctLRU(head_pc)) {
- enum lru_list lru;
- struct mem_cgroup_per_zone *mz;
- /*
- * We hold lru_lock, then, reduce counter directly.
- */
- lru = page_lru(head);
- mz = page_cgroup_zoneinfo(head_pc->mem_cgroup, head);
- MEM_CGROUP_ZSTAT(mz, lru) -= HPAGE_PMD_NR - 1;
- }
+ /*
+ * Tail pages will be added to LRU.
+ * We hold lru_lock,then,reduce counter directly.
+ */
+ lru = page_lru(head);
+ mz = page_cgroup_zoneinfo(head_pc->mem_cgroup, head);
+ MEM_CGROUP_ZSTAT(mz, lru) -= HPAGE_PMD_NR - 1;
}
#endif
@@ -2620,7 +2601,7 @@
parent = mem_cgroup_from_cont(pcg);
ret = __mem_cgroup_try_charge(NULL, gfp_mask, nr_pages, &parent, false);
- if (ret || !parent)
+ if (ret)
goto put_back;
if (nr_pages > 1)
@@ -2667,9 +2648,8 @@
pc = lookup_page_cgroup(page);
ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
- if (ret || !memcg)
+ if (ret == -ENOMEM)
return ret;
-
__mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype);
return 0;
}
@@ -2736,10 +2716,9 @@
if (!page_is_file_cache(page))
type = MEM_CGROUP_CHARGE_TYPE_SHMEM;
- if (!PageSwapCache(page)) {
+ if (!PageSwapCache(page))
ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
- WARN_ON_ONCE(PageLRU(page));
- } else { /* page is swapcache/shmem */
+ else { /* page is swapcache/shmem */
ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &memcg);
if (!ret)
__mem_cgroup_commit_charge_swapin(page, memcg, type);
@@ -2781,11 +2760,16 @@
*memcgp = memcg;
ret = __mem_cgroup_try_charge(NULL, mask, 1, memcgp, true);
css_put(&memcg->css);
+ if (ret == -EINTR)
+ ret = 0;
return ret;
charge_cur_mm:
if (unlikely(!mm))
mm = &init_mm;
- return __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
+ ret = __mem_cgroup_try_charge(mm, mask, 1, memcgp, true);
+ if (ret == -EINTR)
+ ret = 0;
+ return ret;
}
static void
@@ -3245,7 +3229,7 @@
*memcgp = memcg;
ret = __mem_cgroup_try_charge(NULL, gfp_mask, 1, memcgp, false);
css_put(&memcg->css);/* drop extra refcnt */
- if (ret || *memcgp == NULL) {
+ if (ret) {
if (PageAnon(page)) {
lock_page_cgroup(pc);
ClearPageCgroupMigration(pc);
@@ -3255,6 +3239,7 @@
*/
mem_cgroup_uncharge_page(page);
}
+ /* we'll need to revisit this error code (we have -EINTR) */
return -ENOMEM;
}
/*
@@ -3674,7 +3659,7 @@
pc = lookup_page_cgroup(page);
ret = mem_cgroup_move_parent(page, pc, memcg, GFP_KERNEL);
- if (ret == -ENOMEM)
+ if (ret == -ENOMEM || ret == -EINTR)
break;
if (ret == -EBUSY || ret == -EINVAL) {
@@ -5065,9 +5050,9 @@
}
ret = __mem_cgroup_try_charge(NULL,
GFP_KERNEL, 1, &memcg, false);
- if (ret || !memcg)
+ if (ret)
/* mem_cgroup_clear_mc() will do uncharge later */
- return -ENOMEM;
+ return ret;
mc.precharge++;
}
return ret;
