From: Vlastimil Babka <vbabka@suse.cz>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"jlayton@poochiereds.net" <jlayton@poochiereds.net>,
"bfields@fieldses.org" <bfields@fieldses.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"koct9i@gmail.com" <koct9i@gmail.com>,
"aquini@redhat.com" <aquini@redhat.com>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Rik van Riel <riel@redhat.com>,
"rknize@motorola.com" <rknize@motorola.com>,
Gioh Kim <gi-oh.kim@profitbricks.com>,
Sangseok Lee <sangseok.lee@lge.com>,
Chan Gyun Jeong <chan.jeong@lge.com>,
Al Viro <viro@ZenIV.linux.org.uk>,
YiPing Xu <xuyiping@hisilicon.com>
Subject: Re: [PATCH v3 01/16] mm: use put_page to free page instead of putback_lru_page
Date: Tue, 5 Apr 2016 10:20:50 +0200 [thread overview]
Message-ID: <57037562.3040203@suse.cz> (raw)
In-Reply-To: <20160405015402.GA30962@hori1.linux.bs1.fc.nec.co.jp>
On 04/05/2016 03:54 AM, Naoya Horiguchi wrote:
> On Mon, Apr 04, 2016 at 04:46:31PM +0200, Vlastimil Babka wrote:
>> On 04/04/2016 06:45 AM, Naoya Horiguchi wrote:
>>> On Mon, Apr 04, 2016 at 10:39:17AM +0900, Minchan Kim wrote:
> ...
>>>>>
>>>>> Also (but not your fault) the put_page() preceding
>>>>> test_set_page_hwpoison(page)) IMHO deserves a comment saying which
>>>>> pin we are releasing and which one we still have (hopefully? if I
>>>>> read description of da1b13ccfbebe right) otherwise it looks like
>>>>> doing something with a page that we just potentially freed.
>>>>
>>>> Yes, while I read the code, I had same question. I think the releasing
>>>> refcount is for get_any_page.
>>>
>>> As the other callers of page migration do, soft_offline_page expects the
>>> migration source page to be freed at this put_page() (no pin remains.)
>>> The refcount released here is from isolate_lru_page() in __soft_offline_page().
>>> (the pin by get_any_page is released by put_hwpoison_page just after it.)
>>>
>>> .. yes, doing something just after freeing page looks weird, but that's
>>> how PageHWPoison flag works. IOW, many other page flags are maintained
>>> only during one "allocate-free" life span, but PageHWPoison still does
>>> its job beyond it.
>>
>> But what prevents the page from being allocated again between put_page()
>> and test_set_page_hwpoison()? In that case we would be marking page
>> poisoned while still in use, which is the same as marking it while still
>> in use after a failed migration?
>
> Actually nothing prevents that race. But I think that the result of the race
> is that the error page can be reused for allocation, which results in killing
> processes at page fault time. Soft offline is kind of mild/precautious thing
> (for correctable errors that don't require immediate handling), so killing
> processes looks to me an overkill. And marking hwpoison means that we can no
> longer do retry from userspace.
So you agree that this race is a bug? It may turn a soft-offline attempt
into a killed process. In that case we should fix it the same as we are
fixing the failed migration case. Maybe it will be just enough to switch
the test_set_page_hwpoison() and put_page() calls?
> And another practical thing is the race with unpoison_memory() as described
> in commit da1b13ccfbebe. unpoison_memory() properly works only for properly
> poisoned pages, so doing unpoison for in-use hwpoisoned pages is fragile.
> That's why I'd like to avoid setting PageHWPoison for in-use pages if possible.
>
>> (Also, which part prevents pages with PageHWPoison to be allocated
>> again, anyway? I can't find it and test_set_page_hwpoison() doesn't
>> remove from buddy freelists).
>
> check_new_page() in mm/page_alloc.c should prevent reallocation of PageHWPoison.
> As you pointed out, memory error handler doens't remove it from buddy freelists.
Oh, I see. It's using __PG_HWPOISON wrapper, so I didn't notice it when
searching. In any case that results in a bad_page() warning, right? Is
it desirable for a soft-offlined page? If we didn't free poisoned pages
to buddy system, they wouldn't trigger this warning.
> BTW, it might be a bit off-topic, but recently I felt that check_new_page()
> might be improvable, because when check_new_page() returns 1, the whole buddy
> block (not only the bad page) seems to be leaked from buddy freelist.
> For example, if thp (order 9) is requested, and PageHWPoison (or any other
> types of bad pages) is found in an order 9 block, all 512 page are discarded.
> Unpoison can't bring it back to buddy.
> So, some code to split buddy block including bad page (and recovering code from
> unpoison) might be helpful, although that's another story ...
Hm sounds like another argument for not freeing the page to buddy lists
in the first place. Maybe a hook in free_pages_check()?
> Thanks,
> Naoya Horiguchi
>
next prev parent reply other threads:[~2016-04-05 8:20 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-30 7:11 [PATCH v3 00/16] Support non-lru page migration Minchan Kim
2016-03-30 7:12 ` [PATCH v3 01/16] mm: use put_page to free page instead of putback_lru_page Minchan Kim
2016-04-01 12:58 ` Vlastimil Babka
2016-04-04 1:39 ` Minchan Kim
2016-04-04 4:45 ` Naoya Horiguchi
2016-04-04 14:46 ` Vlastimil Babka
2016-04-05 1:54 ` Naoya Horiguchi
2016-04-05 8:20 ` Vlastimil Babka [this message]
2016-04-06 0:54 ` Naoya Horiguchi
2016-04-06 7:57 ` Vlastimil Babka
2016-04-04 5:53 ` Balbir Singh
2016-04-04 6:01 ` Minchan Kim
2016-04-05 3:10 ` Balbir Singh
2016-03-30 7:12 ` [PATCH v3 02/16] mm/compaction: support non-lru movable page migration Minchan Kim
2016-04-01 21:29 ` Vlastimil Babka
2016-04-04 5:12 ` Minchan Kim
2016-04-04 13:24 ` Vlastimil Babka
2016-04-07 2:35 ` Minchan Kim
2016-04-12 8:00 ` Chulmin Kim
2016-04-12 14:25 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 03/16] mm: add non-lru movable page support document Minchan Kim
2016-04-01 14:38 ` Vlastimil Babka
2016-04-04 2:25 ` Minchan Kim
2016-04-04 13:09 ` Vlastimil Babka
2016-04-07 2:27 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 04/16] mm/balloon: use general movable page feature into balloon Minchan Kim
2016-04-05 12:03 ` Vlastimil Babka
2016-04-11 4:29 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 05/16] zsmalloc: keep max_object in size_class Minchan Kim
2016-04-17 15:08 ` Sergey Senozhatsky
2016-03-30 7:12 ` [PATCH v3 06/16] zsmalloc: squeeze inuse into page->mapping Minchan Kim
2016-04-17 15:08 ` Sergey Senozhatsky
2016-04-19 7:40 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 07/16] zsmalloc: remove page_mapcount_reset Minchan Kim
2016-04-17 15:11 ` Sergey Senozhatsky
2016-03-30 7:12 ` [PATCH v3 08/16] zsmalloc: squeeze freelist into page->mapping Minchan Kim
2016-04-17 15:56 ` Sergey Senozhatsky
2016-04-19 7:42 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 09/16] zsmalloc: move struct zs_meta from mapping to freelist Minchan Kim
2016-04-17 15:22 ` Sergey Senozhatsky
2016-03-30 7:12 ` [PATCH v3 10/16] zsmalloc: factor page chain functionality out Minchan Kim
2016-04-18 0:33 ` Sergey Senozhatsky
2016-04-19 7:46 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 11/16] zsmalloc: separate free_zspage from putback_zspage Minchan Kim
2016-04-18 1:04 ` Sergey Senozhatsky
2016-04-19 7:51 ` Minchan Kim
2016-04-19 7:53 ` Sergey Senozhatsky
2016-03-30 7:12 ` [PATCH v3 12/16] zsmalloc: zs_compact refactoring Minchan Kim
2016-04-04 8:04 ` Chulmin Kim
2016-04-04 9:01 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 13/16] zsmalloc: migrate head page of zspage Minchan Kim
2016-04-06 13:01 ` Chulmin Kim
2016-04-07 0:34 ` Chulmin Kim
2016-04-07 0:43 ` Minchan Kim
2016-04-19 6:08 ` Chulmin Kim
2016-04-19 6:15 ` Minchan Kim
2016-03-30 7:12 ` [PATCH v3 14/16] zsmalloc: use single linked list for page chain Minchan Kim
2016-03-30 7:12 ` [PATCH v3 15/16] zsmalloc: migrate tail pages in zspage Minchan Kim
2016-03-30 7:12 ` [PATCH v3 16/16] zram: use __GFP_MOVABLE for memory allocation Minchan Kim
2016-03-30 23:11 ` [PATCH v3 00/16] Support non-lru page migration Andrew Morton
2016-03-31 0:29 ` Sergey Senozhatsky
2016-03-31 0:57 ` Minchan Kim
2016-03-31 0:57 ` Minchan Kim
2016-04-04 13:17 ` John Einar Reitan
2016-04-11 4:35 ` Minchan Kim
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