From: Vlastimil Babka <vbabka@suse.cz>
To: Pavel Tatashin <pasha.tatashin@soleen.com>,
Michal Hocko <mhocko@suse.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline
Date: Wed, 2 Sep 2020 16:55:05 +0200 [thread overview]
Message-ID: <74f2341a-7834-3e37-0346-7fbc48d74df3@suse.cz> (raw)
In-Reply-To: <CA+CK2bBZdN56fmsC2jyY_ju8rQfG2-9hForf1CEdcUVL1+wrrA@mail.gmail.com>
On 9/2/20 4:26 PM, Pavel Tatashin wrote:
> On Wed, Sep 2, 2020 at 10:08 AM Michal Hocko <mhocko@suse.com> wrote:
>>
>> >
>> > Thread#1 - continue
>> > free_unref_page_commit
>> > migratetype = get_pcppage_migratetype(page);
>> > // get old migration type
>> > list_add(&page->lru, &pcp->lists[migratetype]);
>> > // add new page to already drained pcp list
>> >
>> > Thread#2
>> > Never drains pcp again, and therefore gets stuck in the loop.
>> >
>> > The fix is to try to drain per-cpu lists again after
>> > check_pages_isolated_cb() fails.
>>
>> But this means that the page is not isolated and so it could be reused
>> for something else. No?
>
> The page is in a movable zone, has zero references, and the section is
> isolated (i.e. set_pageblock_migratetype(page, MIGRATE_ISOLATE);) is
> set. The page should be offlinable, but it is lost in a pcp list as
> that list is never drained again after the first failure to migrate
> all pages in the range.
Yeah. To answer Michal's "it could be reused for something else" - yes, somebody
could allocate it from the pcplist before we do the extra drain. But then it
becomes "visible again" and the loop in __offline_pages() should catch it by
scan_movable_pages() - do_migrate_range(). And this time the pageblock is
already marked as isolated, so the page (freed by migration) won't end up on the
pcplist again.
next prev parent reply other threads:[~2020-09-02 14:55 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-01 12:46 [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline Pavel Tatashin
2020-09-01 18:37 ` David Rientjes
2020-09-02 14:01 ` Michal Hocko
2020-09-02 14:10 ` Michal Hocko
2020-09-02 14:31 ` Pavel Tatashin
2020-09-02 14:49 ` Vlastimil Babka
2020-09-02 14:08 ` Michal Hocko
2020-09-02 14:26 ` Pavel Tatashin
2020-09-02 14:55 ` Vlastimil Babka [this message]
2020-09-02 15:13 ` Michal Hocko
2020-09-02 15:40 ` Pavel Tatashin
2020-09-02 17:51 ` Vlastimil Babka
2020-09-03 6:38 ` Michal Hocko
2020-09-03 18:20 ` David Hildenbrand
2020-09-03 18:23 ` Pavel Tatashin
2020-09-03 18:31 ` David Hildenbrand
2020-09-04 7:02 ` Michal Hocko
2020-09-04 14:25 ` Pavel Tatashin
2020-09-07 7:26 ` Michal Hocko
2020-09-04 6:32 ` Vlastimil Babka
2020-09-03 7:07 ` Michal Hocko
2020-09-03 13:43 ` Pavel Tatashin
2020-09-03 13:50 ` Vlastimil Babka
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