Messages in this thread | | | Date | Thu, 11 Nov 2021 17:57:55 +0200 | From | Mike Rapoport <> | Subject | Re: [PATCH 4/4] x86/mm: replace GFP_ATOMIC with GFP_KERNEL for direct map allocations |
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On Thu, Nov 11, 2021 at 07:19:40AM -0800, Dave Hansen wrote: > On 11/11/21 3:02 AM, Mike Rapoport wrote: > > From: Mike Rapoport <rppt@linux.ibm.com> > > > > The allocations of the direct map pages are mostly happen very early during > > the system boot and they use either the page table cache in brk area of bss > > or memblock. > > > > The few callers that effectively use page allocator for the direct map > > updates are gart_iommu_init() and memory hotplug. Neither of them happen in > > an atomic context so there is no reason to use GFP_ATOMIC for these > > allocations. > > > > Replace GFP_ATOMIC with GFP_KERNEL to avoid using atomic reserves for > > allocations that do not require that. > > I usually think of the biggest downside of GFP_ATOMIC as being that it > fails more often. But, since we tend not to be low on memory in early > boot, GFP_ATOMIC and GFP_KERNEL end up being pretty close in actual > behavior. > > These allocations also get exposed via init_extra_mapping_*(). But, > those are used via early_initcall()s where GFP_KERNEL is fine too.
Right, I forgot to mention them in the changelog...
> Those are a bit worrying because they're in somewhat nice code, like the > Numascale APIC code. I'm not sure how much use it sees these days. > > I guess if this goes wrong somehow, we'll get some nice splats to tell > us what happened. > > Was this motivated by anything in particular? Or is it a pure cleanup?
The trigger was the discussion about PKS protection for the kernel page tables, but for now I'd say it's pure cleanup.
-- Sincerely yours, Mike.
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