Re: [PATCH 2/5] mm,memory_hotplug: Allocate memmap from the added memory range
From: Oscar Salvador
Date: Mon Jan 25 2021 - 08:48:52 EST
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().
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.
[1] https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-10-songmuchun@xxxxxxxxxxxxx/
--
Oscar Salvador
SUSE L3