On 3/21/2018 6:14 PM, Daniel Vacek Wrote:
On Wed, Mar 21, 2018 at 9:09 AM, Jia He <hejianet@xxxxxxxxx> 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
