Messages in this thread | | | Date | Tue, 8 Aug 2017 13:04:06 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC v5 04/11] mm: VMA sequence count |
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On Tue, Aug 08, 2017 at 04:29:32PM +0530, Anshuman Khandual wrote: > On 06/16/2017 11:22 PM, Laurent Dufour wrote: > > From: Peter Zijlstra <peterz@infradead.org> > > > > First of all, please do mention that its adding a new element into the > vm_area_struct which will act as a sequential lock element and help > in navigating page fault without mmap_sem lock.
You're not making sense, there is no lock, and the lines below clearly state we're adding a sequence count.
> > > Wrap the VMA modifications (vma_adjust/unmap_page_range) with sequence > > counts such that we can easily test if a VMA is changed > > Yeah true. > > > > > The unmap_page_range() one allows us to make assumptions about > > page-tables; when we find the seqcount hasn't changed we can assume > > page-tables are still valid. > > Because unmap_page_range() is the only function which can tear it down ? > Or is there any other reason for this assumption ?
Yep.
> > > > The flip side is that we cannot distinguish between a vma_adjust() and > > the unmap_page_range() -- where with the former we could have > > re-checked the vma bounds against the address. > > Distinguished for what purpose ?
It states. If you know its a vma_adjust we could just check if we're inside the new boundaries and continue. But since we cannot, we have to assume the worst and bail.
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