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From: David Hildenbrand <david@redhat.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	akpm@linux-foundation.org, mhocko@kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz,
	pasha.tatashin@soleen.com
Subject: Re: [PATCH 2/5] mm,memory_hotplug: Allocate memmap from the added memory range
Date: Mon, 25 Jan 2021 12:23:12 +0100	[thread overview]
Message-ID: <f2b82be4-2ff2-65f0-5b44-e6fbb7e610c9@redhat.com> (raw)
In-Reply-To: <20210125111816.GB28363@linux>

On 25.01.21 12:18, Oscar Salvador wrote:
> On Mon, Jan 25, 2021 at 11:57:20AM +0100, David Hildenbrand wrote:
>> I'm confused.
>>
>> 1. Assume we hotplug memory, online it to ZONE_MOVABLE. The vmemmap gets
>> allocated from altmap space.
> 
> The vmemmap could have never been allocated from altmap in case hpage vmemmap
> feature is enabled.
> 
> Have a look at [1].
> If is_hugetlb_free_vmemmap_enabled(), vmemmap_populate() ends up calling
> vmemmap_populate_basepages().

Oh, it calls "vmemmap_populate_basepages(start, end, node, NULL);"

the "NULL" part is the important bit.

> 
> And since no memory was consumed from altmap, and hence altmap_alloc_block_buf()
> was never called, vmem_altmap->alloc will be 0, and memory_block->nr_vmemmap_pages
> will be 0 as well.
> 
> But on a second though, true is that we will get in trouble if hpage vmemmap
> feature ever gets to work with vmemmap_populate_hugepages.
> I will queue that to look in a new future.

This seriously needs comments and documentation. The problem is where to
document as long as one of both series is not merged yet :)

At least in the cover letter, because this is not obvious how both
things will play along.

Thanks!

-- 
Thanks,

David / dhildenb


  reply	other threads:[~2021-01-26  6:25 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-17 13:07 [PATCH 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador
2020-12-17 13:07 ` [PATCH 1/5] mm: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE Oscar Salvador
2021-01-11 16:52   ` David Hildenbrand
2021-01-12  7:26     ` Oscar Salvador
2021-01-12 10:12       ` David Hildenbrand
2021-01-12 11:17         ` Oscar Salvador
2021-01-12 11:17           ` David Hildenbrand
2020-12-17 13:07 ` [PATCH 2/5] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2021-01-18 10:11   ` Oscar Salvador
2021-01-19 13:58   ` David Hildenbrand
2021-01-25 10:39     ` Oscar Salvador
2021-01-25 10:56       ` Oscar Salvador
2021-01-25 11:02         ` David Hildenbrand
2021-01-25 13:36           ` Oscar Salvador
2021-01-25 10:57       ` David Hildenbrand
2021-01-25 11:18         ` Oscar Salvador
2021-01-25 11:23           ` David Hildenbrand [this message]
2020-12-17 13:07 ` [PATCH 3/5] acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2021-01-11 16:53   ` David Hildenbrand
2020-12-17 13:07 ` [PATCH 4/5] powerpc/memhotplug: " Oscar Salvador
2021-01-11 16:55   ` David Hildenbrand
2021-01-12 13:31     ` Oscar Salvador
2020-12-17 13:07 ` [PATCH 5/5] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory Oscar Salvador
2021-01-11  9:05 ` [PATCH 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador

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