Re: [PATCH V2 2/2] powerpc/thp: Serialize pmd clear against a linux page table walk.

On Thu,  7 May 2015 12:53:28 +0530 "Aneesh Kumar K.V" [off-list ref] wrote:

Serialize against find_linux_pte_or_hugepte which does lock-less
lookup in page tables with local interrupts disabled. For huge pages
it casts pmd_t to pte_t. Since format of pte_t is different from
pmd_t we want to prevent transit from pmd pointing to page table
to pmd pointing to huge page (and back) while interrupts are disabled.
We clear pmd to possibly replace it with page table pointer in
different code paths. So make sure we wait for the parallel
find_linux_pte_or_hugepage to finish.

I'm not seeing here any description of the problem which is being
fixed.  Does the patch make the machine faster?  Does the machine
crash?