From: David Hildenbrand <david@redhat.com>
To: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Michal Hocko <mhocko@suse.com>,
stable@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Minchan Kim <minchan@kernel.org>,
Huang Ying <ying.huang@intel.com>,
Wei Yang <richard.weiyang@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps
Date: Mon, 22 Jun 2020 16:11:59 +0200 [thread overview]
Message-ID: <b2c82aca-a132-95fd-4081-d94c1d658eee@redhat.com> (raw)
In-Reply-To: <20200622092221.GA96699@L-31X9LVDL-1304.local>
On 22.06.20 11:22, Wei Yang wrote:
> On Mon, Jun 22, 2020 at 10:43:11AM +0200, David Hildenbrand wrote:
>> On 22.06.20 10:26, Wei Yang wrote:
>>> On Fri, Jun 19, 2020 at 02:59:20PM +0200, David Hildenbrand wrote:
>>>> Especially with memory hotplug, we can have offline sections (with a
>>>> garbage memmap) and overlapping zones. We have to make sure to only
>>>> touch initialized memmaps (online sections managed by the buddy) and that
>>>> the zone matches, to not move pages between zones.
>>>>
>>>> To test if this can actually happen, I added a simple
>>>> BUG_ON(page_zone(page_i) != page_zone(page_j));
>>>> right before the swap. When hotplugging a 256M DIMM to a 4G x86-64 VM and
>>>> onlining the first memory block "online_movable" and the second memory
>>>> block "online_kernel", it will trigger the BUG, as both zones (NORMAL
>>>> and MOVABLE) overlap.
>>>>
>>>> This might result in all kinds of weird situations (e.g., double
>>>> allocations, list corruptions, unmovable allocations ending up in the
>>>> movable zone).
>>>>
>>>> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve memory-side-cache utilization")
>>>> Acked-by: Michal Hocko <mhocko@suse.com>
>>>> Cc: stable@vger.kernel.org # v5.2+
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>> Cc: Minchan Kim <minchan@kernel.org>
>>>> Cc: Huang Ying <ying.huang@intel.com>
>>>> Cc: Wei Yang <richard.weiyang@gmail.com>
>>>> Cc: Mel Gorman <mgorman@techsingularity.net>
>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>> mm/shuffle.c | 18 +++++++++---------
>>>> 1 file changed, 9 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/mm/shuffle.c b/mm/shuffle.c
>>>> index 44406d9977c77..dd13ab851b3ee 100644
>>>> --- a/mm/shuffle.c
>>>> +++ b/mm/shuffle.c
>>>> @@ -58,25 +58,25 @@ module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
>>>> * For two pages to be swapped in the shuffle, they must be free (on a
>>>> * 'free_area' lru), have the same order, and have the same migratetype.
>>>> */
>>>> -static struct page * __meminit shuffle_valid_page(unsigned long pfn, int order)
>>>> +static struct page * __meminit shuffle_valid_page(struct zone *zone,
>>>> + unsigned long pfn, int order)
>>>> {
>>>> - struct page *page;
>>>> + struct page *page = pfn_to_online_page(pfn);
>>>
>>> Hi, David and Dan,
>>>
>>> One thing I want to confirm here is we won't have partially online section,
>>> right? We can add a sub-section to system, but we won't manage it by buddy.
>>
>> Hi,
>>
>> there is still a BUG with sub-section hot-add (devmem), which broke
>> pfn_to_online_page() in corner cases (especially, see the description in
>> include/linux/mmzone.h). We can have a boot-memory section partially
>> populated and marked online. Then, we can hot-add devmem, marking the
>> remaining pfns valid - and as the section is maked online, also as online.
>
> Oh, yes, I see this description.
>
> This means we could have section marked as online, but with a sub-section even
> not added.
>
> While the good news is even the sub-section is not added, but its memmap is
> populated for an early section. So the page returned from pfn_to_online_page()
> is a valid one.
>
> But what would happen, if the sub-section is removed after added? Would
> section_deactivate() release related memmap to this "struct page"?
Just to clarify now that I get your point: No it would not, as it is an
early section, and the early section is not completely empty.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-06-22 14:16 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 12:59 [PATCH v2 0/3] mm/shuffle: fix and cleanups David Hildenbrand
2020-06-19 12:59 ` [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps David Hildenbrand
2020-06-20 1:37 ` Williams, Dan J
2020-06-22 8:26 ` Wei Yang
2020-06-22 8:43 ` David Hildenbrand
2020-06-22 9:22 ` Wei Yang
2020-06-22 9:51 ` David Hildenbrand
2020-06-22 13:10 ` Wei Yang
2020-06-22 14:06 ` David Hildenbrand
2020-06-22 21:55 ` Wei Yang
2020-06-23 7:39 ` David Hildenbrand
2020-06-23 7:55 ` David Hildenbrand
2020-06-23 9:30 ` Wei Yang
2020-07-24 3:08 ` Andrew Morton
2020-07-24 5:45 ` Wei Yang
2020-07-24 8:20 ` David Hildenbrand
2020-06-22 14:11 ` David Hildenbrand [this message]
2020-06-19 12:59 ` [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant David Hildenbrand
2020-06-20 1:41 ` Dan Williams
2020-06-22 7:27 ` David Hildenbrand
2020-06-23 21:15 ` Dan Williams
2020-06-24 9:31 ` David Hildenbrand
2020-06-22 15:32 ` Michal Hocko
2020-06-19 12:59 ` [PATCH v2 3/3] mm/shuffle: remove dynamic reconfiguration David Hildenbrand
2020-06-20 1:49 ` Dan Williams
2020-06-22 7:33 ` David Hildenbrand
2020-06-22 8:37 ` Wei Yang
2020-06-23 22:18 ` Dan Williams
2020-06-22 15:37 ` Michal Hocko
2020-06-23 1:22 ` Wei Yang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b2c82aca-a132-95fd-4081-d94c1d658eee@redhat.com \
--to=david@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=hannes@cmpxchg.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@techsingularity.net \
--cc=mhocko@suse.com \
--cc=minchan@kernel.org \
--cc=richard.weiyang@gmail.com \
--cc=richard.weiyang@linux.alibaba.com \
--cc=stable@vger.kernel.org \
--cc=ying.huang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).