From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Laurent Dufour <ldufour@linux.vnet.ibm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>
Subject: Re: [PATCH v2 1/2] mm: Uncharge poisoned pages
Date: Mon, 8 May 2017 02:58:36 +0000 [thread overview]
Message-ID: <20170508025827.GA4913@hori1.linux.bs1.fc.nec.co.jp> (raw)
In-Reply-To: <20170502185507.GB19165@dhcp22.suse.cz>
On Tue, May 02, 2017 at 08:55:07PM +0200, Michal Hocko wrote:
> On Tue 02-05-17 16:59:30, Laurent Dufour wrote:
> > On 28/04/2017 15:48, Michal Hocko wrote:
> [...]
> > > This is getting quite hairy. What is the expected page count of the
> > > hwpoison page?
>
> OK, so from the quick check of the hwpoison code it seems that the ref
> count will be > 1 (from get_hwpoison_page).
>
> > > I guess we would need to update the VM_BUG_ON in the
> > > memcg uncharge code to ignore the page count of hwpoison pages if it can
> > > be arbitrary.
> >
> > Based on the experiment I did, page count == 2 when isolate_lru_page()
> > succeeds, even in the case of a poisoned page.
>
> that would make some sense to me. The page should have been already
> unmapped therefore but memory_failure increases the ref count and 1 is
> for isolate_lru_page().
# sorry for late reply, I was on holidays last week...
Right, and the refcount taken for memory_failure is not freed after
memory_failure() returns. unpoison_memory() does free the refcount.
>
> > In my case I think this
> > is because the page is still used by the process which is calling madvise().
> >
> > I'm wondering if I'm looking at the right place. May be the poisoned
> > page should remain attach to the memory_cgroup until no one is using it.
> > In that case this means that something should be done when the page is
> > off-lined... I've to dig further here.
>
> No, AFAIU the page will not drop the reference count down to 0 in most
> cases. Maybe there are some scenarios where this can happen but I would
> expect that the poisoned page will be mapped and in use most of the time
> and won't drop down 0. And then we should really uncharge it because it
> will pin the memcg and make it unfreeable which doesn't seem to be what
> we want. So does the following work reasonable? Andi, Johannes, what do
> you think? I cannot say I would be really comfortable touching hwpoison
> code as I really do not understand the workflow. Maybe we want to move
> this uncharge down to memory_failure() right before we report success?
memory_failure() can be called for any types of page (including slab or
any kernel/driver pages), and the reported problem seems happen only on
in-use user pages, so uncharging in delete_from_lru_cache() as done below
looks better to me.
> ---
> From 8bf0791bcf35996a859b6d33fb5494e5b53de49d Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Tue, 2 May 2017 20:32:24 +0200
> Subject: [PATCH] hwpoison, memcg: forcibly uncharge LRU pages
>
> Laurent Dufour has noticed that hwpoinsoned pages are kept charged. In
> his particular case he has hit a bad_page("page still charged to cgroup")
> when onlining a hwpoison page.
> While this looks like something that shouldn't
> happen in the first place because onlining hwpages and returning them to
> the page allocator makes only little sense it shows a real problem.
>
> hwpoison pages do not get freed usually so we do not uncharge them (at
> least not since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")).
> Each charge pins memcg (since e8ea14cc6ead ("mm: memcontrol: take a css
> reference for each charged page")) as well and so the mem_cgroup and the
> associated state will never go away. Fix this leak by forcibly
> uncharging a LRU hwpoisoned page in delete_from_lru_cache(). We also
> have to tweak uncharge_list because it cannot rely on zero ref count
> for these pages.
>
> Fixes: 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API")
> Reported-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> ---
> mm/memcontrol.c | 2 +-
> mm/memory-failure.c | 7 +++++++
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 16c556ac103d..4cf26059adb1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5527,7 +5527,7 @@ static void uncharge_list(struct list_head *page_list)
> next = page->lru.next;
>
> VM_BUG_ON_PAGE(PageLRU(page), page);
> - VM_BUG_ON_PAGE(page_count(page), page);
> + VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page);
>
> if (!page->mem_cgroup)
> continue;
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 8a6bd3a9eb1e..4497d9619bb4 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -541,6 +541,13 @@ static int delete_from_lru_cache(struct page *p)
> */
> ClearPageActive(p);
> ClearPageUnevictable(p);
> +
> + /*
> + * Poisoned page might never drop its ref count to 0 so we have to
> + * uncharge it manually from its memcg.
> + */
> + mem_cgroup_uncharge(p);
> +
> /*
> * drop the page count elevated by isolate_lru_page()
> */
> --
> 2.11.0
>
> --
> Michal Hocko
> SUSE Labs
>
next prev parent reply other threads:[~2017-05-08 2:59 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-25 14:27 [PATCH v2 0/2] BUG raised when onlining HWPoisoned page Laurent Dufour
2017-04-25 14:27 ` [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour
2017-04-25 23:48 ` Naoya Horiguchi
2017-04-26 1:54 ` Balbir Singh
2017-04-26 2:34 ` Naoya Horiguchi
2017-04-26 3:45 ` Balbir Singh
2017-04-26 4:46 ` Naoya Horiguchi
2017-04-26 8:59 ` Balbir Singh
2017-04-28 9:32 ` Laurent Dufour
2017-04-27 14:37 ` Michal Hocko
2017-04-27 20:51 ` Andi Kleen
2017-04-28 6:07 ` Michal Hocko
2017-04-28 7:31 ` Michal Hocko
2017-04-28 9:17 ` Laurent Dufour
2017-04-28 13:48 ` Michal Hocko
2017-05-02 14:59 ` Laurent Dufour
2017-05-02 18:55 ` Michal Hocko
2017-05-03 11:34 ` Laurent Dufour
2017-05-04 1:21 ` Balbir Singh
2017-05-08 10:42 ` Laurent Dufour
2017-05-09 1:41 ` Balbir Singh
2017-05-08 2:58 ` Naoya Horiguchi [this message]
2017-05-09 9:18 ` Michal Hocko
2017-05-09 22:59 ` Naoya Horiguchi
2017-04-25 14:27 ` [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Laurent Dufour
2017-04-26 2:10 ` Balbir Singh
2017-04-26 3:13 ` Naoya Horiguchi
2017-04-28 2:51 ` Balbir Singh
2017-04-28 6:30 ` Michal Hocko
2017-04-28 6:50 ` Michal Hocko
2017-04-28 6:51 ` Michal Hocko
2017-05-10 7:41 ` Michal Hocko
2018-01-17 23:03 ` Andrew Morton
2018-01-23 18:15 ` Laurent Dufour
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