From: David Hildenbrand <david@redhat.com>
To: Oscar Salvador <osalvador@suse.de>, Zi Yan <ziy@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Vlastimil Babka <vbabka@suse.cz>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [PATCH v3 1/5] mm,memory_hotplug: Allocate memmap from the added memory range
Date: Mon, 8 Mar 2021 15:06:49 +0100 [thread overview]
Message-ID: <51662b87-35bd-ff18-17dd-b2a99d1095d7@redhat.com> (raw)
In-Reply-To: <YEYvAzPoaOkrsEaf@localhost.localdomain>
On 08.03.21 15:04, Oscar Salvador wrote:
> On Sun, Mar 07, 2021 at 10:16:36PM -0500, Zi Yan wrote:
>> +Mike for hugetlb discussion.
>>
>> Just thinking about how it might impact gigantic page allocation like hugetlb.
>> When MHP_MEMMAP_ON_MEMORY is on, memmap pages are placed at the beginning
>> of each hot added memory block, so available PFNs from two consecutive
>> hot added memory blocks are not all contiguous, separated by memmap pages.
>> If the memory block size is <= 1GB, there is no way of reserving gigantic
>> pages for hugetlb during runtime using alloc_contig_pages from any hot
>> added memory. Am I getting this right?
>
> Yes, that is why it is stated both in boot parameter documentation and
> patch changelog that this feature does not play well in those setups
> where your workload is in need of large contiguous chunks of memory,
> that being gigantic hugetlb or just normal memory.
>
>> I see this implication is documented at the high level in patch 3. Just
>> wonder if we want to be more specific. Or hugetlb is rarely used along
>> with hot-add memory.
>
> I think it is quite normal to see hugetlb and hotplug operations in the
> same environment.
> One thing excludes the other, just need to be careful when it comes to
> potential pitfalls during offline operations.
>
> I guess we could mention hugetlb pages in the documentation, if it feels
> it is necesary.
Runtime allocation of gigantic pages without CMA is absolutely
unreliable either way. IMHO, a tunable for the admin is good enough.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-03-08 14:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 9:59 [PATCH v3 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador
2021-03-04 9:59 ` [PATCH v3 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2021-03-08 3:16 ` Zi Yan
2021-03-08 14:04 ` Oscar Salvador
2021-03-08 14:06 ` David Hildenbrand [this message]
2021-03-04 9:59 ` [PATCH v3 2/5] acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2021-03-04 10:00 ` [PATCH v3 3/5] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory Oscar Salvador
2021-03-05 15:35 ` David Hildenbrand
2021-03-08 15:46 ` Oscar Salvador
2021-03-04 10:00 ` [PATCH v3 4/5] x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE Oscar Salvador
2021-03-05 15:32 ` David Hildenbrand
2021-03-07 22:14 ` Oscar Salvador
2021-03-04 10:00 ` [PATCH v3 5/5] arm64/Kconfig: " Oscar Salvador
2021-03-05 15:32 ` David Hildenbrand
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