Re: [PATCH 4/4] memcg: fix rmdir, force_empty with THP
From: Johannes Weiner <hannes@cmpxchg.org>
Date: 2011-01-20 13:41:19
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On Tue, Jan 18, 2011 at 11:43:48AM +0900, KAMEZAWA Hiroyuki wrote:
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Now, when THP is enabled, memcg's rmdir() function is broken because move_account() for THP page is not supported. This will cause account leak or -EBUSY issue at rmdir(). This patch fixes the issue by supporting move_account() THP pages. Changelog: - style fix. - add compound_lock for avoiding races. Signed-off-by: KAMEZAWA Hiroyuki <redacted> --- mm/memcontrol.c | 37 ++++++++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 11 deletions(-) Index: mmotm-0107/mm/memcontrol.c ===================================================================--- mmotm-0107.orig/mm/memcontrol.c +++ mmotm-0107/mm/memcontrol.c
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@@ -2267,6 +2274,8 @@ static int mem_cgroup_move_parent(struct struct cgroup *cg = child->css.cgroup; struct cgroup *pcg = cg->parent; struct mem_cgroup *parent; + int charge = PAGE_SIZE;
No need to initialize, you assign it unconditionally below. It's also a bit unfortunate that the parameter/variable with this meaning appears under a whole bunch of different names. page_size, charge_size, and now charge. Could you stick with page_size?
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@@ -2278,17 +2287,23 @@ static int mem_cgroup_move_parent(struct goto out; if (isolate_lru_page(page)) goto put; + /* The page is isolated from LRU and we have no race with splitting */ + charge = PAGE_SIZE << compound_order(page);
Why is LRU isolation preventing the splitting? I think we need the compound lock to get a stable read, like compound_trans_order() does. Hannes
parent = mem_cgroup_from_cont(pcg); - ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, - PAGE_SIZE); + ret = __mem_cgroup_try_charge(NULL, gfp_mask, &parent, false, charge); if (ret || !parent) goto put_back; - ret = mem_cgroup_move_account(pc, child, parent, true); + if (charge > PAGE_SIZE) + flags = compound_lock_irqsave(page); + + ret = mem_cgroup_move_account(pc, child, parent, true, charge); if (ret) - mem_cgroup_cancel_charge(parent, PAGE_SIZE); + mem_cgroup_cancel_charge(parent, charge); put_back: + if (charge > PAGE_SIZE) + compound_unlock_irqrestore(page, flags); putback_lru_page(page); put: put_page(page);
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