On 03.03.2020 18:48, Andrey Ryabinin wrote:
> Instead of trylock'ing the page, use the lru_lock to prevent the
> racing against mem_cgroup_migrate(). So the memcg_move_account() doesn't
> depend on hung IO.
>
> The trylock seems to be needed to prevent mem_cgroup_migrate() to see
> disbalanced pc->mem_cgroup && pc->flags state. We could achieve the same
> by using lru_lock instead. memcg_move_account() only works with isolated
> from LRU pages, so it can race only with mem_cgroup_migrate() called
> with lrucare=true, otherwise the page is not on LRU so the
> memcg_move_account()
> can't see it.
>
> https://jira.sw.ru/browse/PSBM-101639
> https://jira.sw.ru/browse/PSBM-101757
> https://jira.sw.ru/browse/PSBM-94117
> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
> ---
> mm/memcontrol.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f4629123e7fb..bfb5bbdf9ecb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3939,7 +3939,7 @@ static int mem_cgroup_move_account(struct page *page,
> struct mem_cgroup *to)
> {
> unsigned long flags;
> - int ret;
> + int ret, isolated;
>
> VM_BUG_ON(from == to);
> VM_BUG_ON_PAGE(PageLRU(page), page);
> @@ -3958,8 +3958,7 @@ static int mem_cgroup_move_account(struct page *page,
> * of its source page while we change it: page migration takes
> * both pages off the LRU, but page cache replacement doesn't.
> */
> - if (!trylock_page(page))
> - goto out;
> + lock_page_lru(page, &isolated);
Does this race with try_get_mem_cgroup_from_page()?
> ret = -EINVAL;
> if (!PageCgroupUsed(pc) || pc->mem_cgroup != from)
> @@ -3992,7 +3991,7 @@ static int mem_cgroup_move_account(struct page *page,
> memcg_check_events(from, page);
> local_irq_restore(flags);
> out_unlock:
> - unlock_page(page);
> + unlock_page_lru(page, isolated);
> out:
> return ret;
> }
> @@ -7754,6 +7753,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct
> page *newpage,
> {
> unsigned int nr_pages = 1;
> struct page_cgroup *pc;
> + struct mem_cgroup *memcg;
> int isolated;
>
> VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
> @@ -7787,17 +7787,18 @@ void mem_cgroup_migrate(struct page *oldpage, struct
> page *newpage,
> if (lrucare)
> lock_page_lru(oldpage, &isolated);
>
> + memcg = READ_ONCE(pc->mem_cgroup);
> pc->flags = 0;
>
> if (lrucare)
> unlock_page_lru(oldpage, isolated);
>
> local_irq_disable();
> - mem_cgroup_charge_statistics(pc->mem_cgroup, oldpage, -nr_pages);
> - memcg_check_events(pc->mem_cgroup, oldpage);
> + mem_cgroup_charge_statistics(memcg, oldpage, -nr_pages);
> + memcg_check_events(memcg, oldpage);
> local_irq_enable();
>
> - commit_charge(newpage, pc->mem_cgroup, nr_pages, lrucare);
> + commit_charge(newpage, memcg, nr_pages, lrucare);
> }
>
> static int __init cgroup_memory(char *s)
>
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