From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>, lantianyu1986@gmail.com
Cc: kys@microsoft.com, haiyangz@microsoft.com,
sthemmin@microsoft.com, sashal@kernel.org,
akpm@linux-foundation.org, michael.h.kelley@microsoft.com,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, vkuznets@redhat.com,
eric.devolder@oracle.com, vbabka@suse.cz, osalvador@suse.de,
pavel.tatashin@microsoft.com, rppt@linux.ibm.com
Subject: Re: [RFC PATCH V2 2/10] mm: expose is_mem_section_removable() symbol
Date: Fri, 10 Jan 2020 14:41:36 +0100 [thread overview]
Message-ID: <99a6db0c-6d73-d982-58b3-7a0172748ae4@redhat.com> (raw)
In-Reply-To: <20200107133623.GJ32178@dhcp22.suse.cz>
On 07.01.20 14:36, Michal Hocko wrote:
> On Tue 07-01-20 21:09:42, lantianyu1986@gmail.com wrote:
>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>
>> Hyper-V balloon driver will use is_mem_section_removable() to
>> check whether memory block is removable or not when receive
>> memory hot remove msg. Expose it.
>
> I do not think this is a good idea. The check is inherently racy. Why
> cannot the balloon driver simply hotremove the region when asked?
>
It's not only racy, it also gives no guarantees. False postives and
false negatives are possible.
If you want to avoid having to loop forever trying to offline when
calling offline_and_remove_memory(), you could try to
alloc_contig_range() the memory first and then play the
PG_offline+notifier game like virtio-mem.
I don't remember clearly, but I think pinned pages can make offlining
loop for a long time. And I remember there were other scenarios as well
(including out of memory conditions and similar).
I sent an RFC [1] for powerpc/memtrace that does the same (just error
handling is more complicated as it wants to offline and remove multiple
consecutive memory blocks) - if you want to try to go down that path.
[1] https://lkml.kernel.org/r/20191217123851.8854-1-david@redhat.com
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-01-10 13:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-07 13:09 [RFC PATCH V2 00/10] x86/Hyper-V: Add Dynamic memory hot-remove function lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 1/10] mm/resource: Move child to new resource when release mem region lantianyu1986
2020-01-20 18:34 ` Michael Kelley
2020-01-20 19:20 ` Michael Kelley
2020-01-07 13:09 ` [RFC PATCH V2 2/10] mm: expose is_mem_section_removable() symbol lantianyu1986
2020-01-07 13:36 ` Michal Hocko
2020-01-10 13:41 ` David Hildenbrand [this message]
2020-01-13 14:49 ` [EXTERNAL] " Tianyu Lan
2020-01-13 15:01 ` David Hildenbrand
2020-01-14 9:50 ` Michal Hocko
2020-01-17 16:35 ` Tianyu Lan
2020-01-20 14:14 ` Michal Hocko
2020-01-07 13:09 ` [RFC PATCH V2 3/10] x86/Hyper-V/Balloon: Replace hot-add and balloon up works with a common work lantianyu1986
2020-01-20 19:12 ` Michael Kelley
2020-01-07 13:09 ` [RFC PATCH V2 4/10] x86/Hyper-V/Balloon: Convert spin lock ha_lock to mutex lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 5/10] x86/Hyper-V/Balloon: Avoid releasing ha_lock when traverse ha_region_list lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 6/10] x86/Hyper-V/Balloon: Enable mem hot-remove capability lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 7/10] x86/Hyper-V/Balloon: Handle mem hot-remove request lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 8/10] x86/Hyper-V/Balloon: Handle request with non-aligned page number lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 9/10] x86/Hyper-V/Balloon: Hot add mem in the gaps of hot add region lantianyu1986
2020-01-07 13:09 ` [RFC PATCH V2 10/10] x86/Hyper-V: Workaround Hyper-V unballoon msg bug lantianyu1986
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