Messages in this thread | | | Subject | Re: [PATCH 1/4] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn() | From | Jia He <> | Date | Wed, 21 Mar 2018 20:28:18 +0800 |
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On 3/21/2018 6:14 PM, Daniel Vacek Wrote: > On Wed, Mar 21, 2018 at 9:09 AM, Jia He <hejianet@gmail.com> wrote: >> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns >> where possible") optimized the loop in memmap_init_zone(). But there is >> still some room for improvement. E.g. if pfn and pfn+1 are in the same >> memblock region, we can simply pfn++ instead of doing the binary search >> in memblock_next_valid_pfn. > There is a revert-mm-page_alloc-skip-over-regions-of-invalid-pfns-where-possible.patch > in -mm reverting b92df1de5d289c0b as it is fundamentally wrong by > design causing system panics on some machines with rare but still > valid mappings. Basically it skips valid pfns which are outside of > usable memory ranges (outside of memblock memory regions). Thanks for the infomation. quote from you patch description: >But given some specific memory mapping on x86_64 (or more generally theoretically anywhere but on arm with CONFIG_HAVE_ARCH_PFN_VALID) > the implementation also skips valid pfns which is plain wrong and causes > 'kernel BUG at mm/page_alloc.c:1389!'
Do you think memblock_next_valid_pfn can remain to be not reverted on arm64 with CONFIG_HAVE_ARCH_PFN_VALID? Arm64 can benifit from this optimization.
Cheers, Jia
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