(2012/03/22 22:38), Michal Hocko wrote:
> On Mon 19-03-12 17:03:42, KAMEZAWA Hiroyuki wrote:
> [...]
>> @@ -1237,8 +1237,6 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
>> pc = lookup_page_cgroup(page);
>> if (!PageCgroupUsed(pc))
>> return NULL;
>> - /* Ensure pc's mem_cgroup is visible after reading PCG_USED. */
>> - smp_rmb();
>> mz = page_cgroup_zoneinfo(pc_to_mem_cgroup(pc), page);
>> return &mz->reclaim_stat;
>> }
>> @@ -2491,16 +2489,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
>> }
>> }
>>
>> - pc_set_mem_cgroup(pc, memcg);
>> - /*
>> - * We access a page_cgroup asynchronously without lock_page_cgroup().
>> - * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
>> - * is accessed after testing USED bit. To make pc's mem_cgroup visible
>> - * before USED bit, we need memory barrier here.
>> - * See mem_cgroup_add_lru_list(), etc.
>> - */
>> - smp_wmb();
>> - SetPageCgroupUsed(pc);
>> + pc_set_mem_cgroup(pc, memcg, BIT(PCG_USED) | BIT(PCG_LOCK));
>
> This is not nice. Maybe we need two variants (pc_set_mem_cgroup[_flags])?
>
Sure. I'll add that.
>> if (lrucare) {
>> if (was_on_lru) {
>> @@ -2529,7 +2518,6 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
>>
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>
>> -#define PCGF_NOCOPY_AT_SPLIT ((1 << PCG_LOCK) | (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.
>> @@ -2547,9 +2535,7 @@ void mem_cgroup_split_huge_fixup(struct page *head)
>> return;
>> for (i = 1; i < HPAGE_PMD_NR; i++) {
>> pc = head_pc + i;
>> - pc_set_mem_cgroup(pc, memcg);
>> - smp_wmb();/* see __commit_charge() */
>> - pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;
>> + pc_set_mem_cgroup(pc, memcg, BIT(PCG_USED));
>
> Maybe it would be cleaner to remove PCGF_NOCOPY_AT_SPLIT in a separate patch with
> VM_BUG_ON(!head_pc->flags & BIT(PCG_USED))?
>
Hm, ok. I'll divide this patch.
>> }
>> }
>> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>> @@ -2616,7 +2602,7 @@ static int mem_cgroup_move_account(struct page *page,
>> __mem_cgroup_cancel_charge(from, nr_pages);
>>
>> /* caller should have done css_get */
>> - pc_set_mem_cgroup(pc, to);
>> + pc_set_mem_cgroup(pc, to, BIT(PCG_USED) | BIT(PCG_LOCK));
>
> Same here.
>
pc_set_mem_cgroup_flags() ?
Thanks,
-Kame
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