Messages in this thread | | | Subject | Re: [PATCH v4 1/5] mm,memory_hotplug: Allocate memmap from the added memory range | From | David Hildenbrand <> | Date | Thu, 18 Mar 2021 13:05:39 +0100 |
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On 18.03.21 13:03, Oscar Salvador wrote: > On Thu, Mar 18, 2021 at 12:24:16PM +0100, David Hildenbrand wrote: >> I don't follow. 2MB == 2MB. And if there would be difference then we would >> be in the problem I brought up: vmemmap code allocating too much via the >> altmap, which can be very bad because might be populating more vmemmap than >> we actually need. > > Yes, I meant to say nr_vmemmap_pages won't match, or IOW, won't have the > same meaning. > The end result is the same. > >> vmemmap_size = 512 * 4KiB = 2 MiB. >> >> That calculation wasn't very useful (/ PAGE_SIZE * PAGE_SIZE)? > > Yeah, somewhat redundant. > >> >>> unsigned long remaining_size = size - vmemmap_size; >> >> And here we could get something like >> >> remaining_size = 2 GiB - 2 MiB > > Yes, vmemmap_size would need to scale with nr_sections to be relative to > size. > > Just wanted to bring it up, because somene might wonder > "ok, why do we have altmap->nr_pfns = X, and here nr_vmemmap_pages > is Y" > > It was an effort to make it consistent, although I see it would bring > more confusion other than anything, so disregard.
I am also unhappy that we have to replicate the same computation at two places, but I don't see an easy way to avoid that ... we have to trust on vmemmap code to do the right thing either way :(
-- Thanks,
David / dhildenb
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