From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
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 11:40:53 -0400 [thread overview]
Message-ID: <CA+CK2bDVq5UTJfgFuhzPrAGbrFOMcR=Cm1A0nue7M2z+yMac3Q@mail.gmail.com> (raw)
In-Reply-To: <20200902151306.GL4617@dhcp22.suse.cz>
> > >> 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.
>
> So the page block is marked MIGRATE_ISOLATE but the allocation itself
> could be used for non migrateable objects. Or does anything prevent that
> from happening?
Vlastimil is right, we could allocate from pcplist, if someone
requests allocation, nothing from what I can tell prevents that, and
we will immediately migrate that page in do_migrate_range().
> We really do depend on isolation to not allow reuse when offlining.
Once a page is isolated it is not re-used but here this page is not
isolated because of the race between adding to pcp and isolation.
Draining the second time on a failure fixes the race.
Pasha
next prev parent reply other threads:[~2020-09-02 15:42 UTC|newest]
Thread overview: 31+ 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 14:31 ` Sasha Levin
2020-09-01 18:37 ` David Rientjes
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 14:31 ` 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 14:26 ` Pavel Tatashin
2020-09-02 14:55 ` Vlastimil Babka
2020-09-02 15:13 ` Michal Hocko
2020-09-02 15:40 ` Pavel Tatashin [this message]
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 18:23 ` Pavel Tatashin
2020-09-03 18:31 ` David Hildenbrand
2020-09-04 7:02 ` Michal Hocko
2020-09-04 14:25 ` Pavel Tatashin
2020-09-04 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 13:43 ` Pavel Tatashin
2020-09-03 13:50 ` Vlastimil Babka
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