Messages in this thread | | | Date | Thu, 22 Mar 2018 13:52:04 +0100 | From | Eugeniu Rosca <> | Subject | Re: [PATCH 1/4] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn() |
| |
On Wed, Mar 21, 2018 at 08:28:18PM +0800, Jia He wrote: > > > 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.
I confirm that the boot time of Rcar-H3 arm64 platform greatly benefits from v4.11-rc1 commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns where possible"). The startup improvement is roughly ~140ms, which will be lost if the mentioned commit is reverted.
For more details on my measurements, please see linux-next commit 283f1645e236 ("mm: page_alloc: skip over regions of invalid pfns on UMA").
Whichever way you decide to go forward (reimplement/fix b92df1de5d28 or create an <arch>_next_valid_pfn), I am willing to participate in testing your proposals on RCAR SoCs. TIA.
Thanks, Eugeniu.
| |