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Date: Tue, 11 Jul 2017 16:38:46 +0530 From: Anshuman Khandual <khandual@...ux.vnet.ibm.com> To: Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org> Cc: Anshuman Khandual <khandual@...ux.vnet.ibm.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, mike.kravetz@...cle.com Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable() On 07/11/2017 12:26 PM, Vlastimil Babka wrote: > On 07/11/2017 08:50 AM, Michal Hocko wrote: >> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote: >>> On 07/11/2017 08:03 AM, Michal Hocko wrote: >>>> >>>> Are you telling me that two if conditions cause more than a second >>>> difference? That sounds suspicious. >>> >>> It's removing also a call to get_unmapped_area(), AFAICS. That means a >>> vma search? >> >> Ohh, right. I have somehow missed that. Is this removal intentional? > > I think it is: "Checking for availability of virtual address range at > the end of the VMA for the incremental size is also reduntant at this > point." > >> The >> changelog is silent about it. > > It doesn't explain why it's redundant, indeed. Unfortunately, the commit > f106af4e90ea ("fix checks for expand-in-place mremap") which added this, > also doesn't explain why it's needed. Its redundant because there are calls to get_unmapped_area() down the line in the function whose failure will anyway fail the expansion of the VMA.
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