From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
virtualization@lists.linux-foundation.org,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Juergen Gross <jgross@suse.com>,
Pavel Tatashin <pavel.tatashin@microsoft.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
Anthony Yznaga <anthony.yznaga@oracle.com>,
Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Oscar Salvador <osalvador@suse.de>,
Pingfan Liu <kernelfans@gmail.com>, Qian Cai <cai@lca.pw>,
Dan Williams <dan.j.williams@intel.com>,
Mel Gorman <mgorman@techsingularity.net>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Wei Yang <richardw.yang@linux.intel.com>,
Alexander Potapenko <glider@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
Matthew Wilcox <willy@infradead.org>, Yu Zhao <yuzhao@google.com>,
Minchan Kim <minchan@kernel.org>,
Yang Shi <yang.shi@linux.alibaba.com>,
Ira Weiny <ira.weiny@intel.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: [PATCH RFC v3 6/9] mm: Allow to offline PageOffline() pages with a reference count of 0
Date: Thu, 24 Oct 2019 10:51:28 +0200 [thread overview]
Message-ID: <ba7164c9-b98e-0ce1-358e-8b0d45fe3f48@redhat.com> (raw)
In-Reply-To: <20191024084241.GV17610@dhcp22.suse.cz>
On 24.10.19 10:42, Michal Hocko wrote:
> On Wed 23-10-19 12:03:51, David Hildenbrand wrote:
>>> Do you see any downsides?
>>
>> The only downside I see is that we get more false negatives on
>> has_unmovable_pages(), eventually resulting in the offlining stage after
>> isolation to loop forever (as some PageOffline() pages are not movable
>> (especially, XEN balloon, HyperV balloon), there won't be progress).
>>
>> I somewhat don't like forcing everybody that uses PageOffline() (especially
>> all users of balloon compaction) to implement memory notifiers just to avoid
>> that. Maybe, we even want to use PageOffline() in the future in the core
>> (e.g., for memory holes instead of PG_reserved or similar).
>
> There is only a handful of those and we need to deal with them anyway.
> If you do not want to enforce them to create their own notifiers then we
> can accomodate the hotplug code. __test_page_isolated_in_pageblock resp.
Yeah, I would prefer offlining code to be able to deal with that without
notifier changes for all users.
> the call chain up can distinguish temporary and permanent failures
> (EAGAIN vs. EBUSY). The current state when we always return EBUSY and
> keep retrying for ever is not optimal at all, right? A referenced PageOffline
Very right!
> could be an example of EBUSY all other failures where we are effectively
> waiting for pages to get freed finaly would be EAGAIN.
We have to watch out for PageOffline() pages that are actually movable
(balloon compaction). But that doesn't sound too hard.
>
> It is a bit late in the process because a large portion of the work has
> been done already but this doesn't sound like something to lose sleep
> over.
>
Right. I'll look into that to find out if this would work. And see if I
can reproduce what I described at all (theoretical thoughts) :)
Again, thanks for looking into this Michal!
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-10-24 8:51 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-19 14:22 [PATCH RFC v3 0/9] virtio-mem: paravirtualized memory David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 1/9] ACPI: NUMA: export pxm_to_node David Hildenbrand
2019-09-23 10:13 ` David Hildenbrand
2019-09-23 10:36 ` Michal Hocko
2019-09-23 10:39 ` David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 2/9] virtio-mem: Paravirtualized memory hotplug David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 3/9] virtio-mem: Paravirtualized memory hotunplug part 1 David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 4/9] mm: Export alloc_contig_range() / free_contig_range() David Hildenbrand
2019-10-16 11:20 ` Michal Hocko
2019-10-16 12:31 ` David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 5/9] virtio-mem: Paravirtualized memory hotunplug part 2 David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 6/9] mm: Allow to offline PageOffline() pages with a reference count of 0 David Hildenbrand
2019-10-16 11:43 ` Michal Hocko
2019-10-16 12:50 ` David Hildenbrand
2019-10-16 13:45 ` Michal Hocko
2019-10-16 13:55 ` David Hildenbrand
2019-10-16 14:09 ` Michal Hocko
2019-10-16 14:16 ` David Hildenbrand
2019-10-16 13:59 ` David Hildenbrand
2019-10-16 13:45 ` David Hildenbrand
2019-10-16 14:03 ` Michal Hocko
2019-10-16 14:14 ` David Hildenbrand
2019-10-18 8:15 ` Michal Hocko
2019-10-18 8:50 ` David Hildenbrand
2019-10-18 11:20 ` Michal Hocko
2019-10-18 12:35 ` David Hildenbrand
2019-10-22 12:23 ` Michal Hocko
2019-10-22 14:02 ` David Hildenbrand
2019-10-23 9:43 ` Michal Hocko
2019-10-23 10:03 ` David Hildenbrand
2019-10-24 8:42 ` Michal Hocko
2019-10-24 8:51 ` David Hildenbrand [this message]
2019-10-25 11:28 ` [PATCH RFC] mm: Allow to offline unmovable PageOffline() pages if the driver agrees David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 7/9] virtio-mem: Allow to offline partially unplugged memory blocks David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 8/9] mm/memory_hotplug: Introduce offline_and_remove_memory() David Hildenbrand
2019-10-16 11:47 ` Michal Hocko
2019-10-16 12:57 ` David Hildenbrand
2019-09-19 14:22 ` [PATCH RFC v3 9/9] virtio-mem: Offline and remove completely unplugged memory blocks David Hildenbrand
2019-10-16 8:12 ` [PATCH RFC v3 0/9] virtio-mem: paravirtualized memory David Hildenbrand
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