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SubjectRe: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb_mm
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On Wed, 2012-05-16 at 21:34 +0800, Alex Shi wrote:
>
> So, if the minimum change of tlb->start/end can be protected by
> HAVE_GENERIC_MMU_GATHER, it is safe and harmless, am I right?
>
safe yes, but not entirely harmless. A quick look seems to suggest you
fail for VM_HUGETLB. If your mmu_gather spans a vma with VM_HUGETLB
you'll do a regular range flush not a full mm flush like the other paths
do.

Anyway, I did a quick refresh of my series on a recent -tip tree:

git://git.kernel.org/pub/scm/linux/kernel/git/peterz/mmu.git tlb-unify

With that all you need is to "select HAVE_MMU_GATHER_RANGE" for x86 and
implement a useful flush_tlb_range().

In particular, see:
http://git.kernel.org/?p=linux/kernel/git/peterz/mmu.git;a=commitdiff;h=05e53144177e6242fda404045f50f48114bcf185;hp=2cd7dc710652127522392f4b7ecb5fa6e954941e

I've slightly changed the code to address an open issue with the
vm_flags tracking. We now force flush the mmu_gather whenever VM_HUGETLB
flips because most (all?) archs that look at that flag expect pure huge
pages and not a mixture.

I've seem to have misplaced my cross-compiler set, so I've only compiled
x86-64 for now.


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