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Date: Tue, 11 Jul 2017 13:22:53 +0200 From: Michal Hocko <mhocko@...nel.org> To: Anshuman Khandual <khandual@...ux.vnet.ibm.com> Cc: Vlastimil Babka <vbabka@...e.cz>, 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 Tue 11-07-17 16:38:46, Anshuman Khandual wrote: > 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. mremap code is quite complex and I am not sure you are right here. Anyway, please make sure you document why you believe those checks are not needed when resubmitting your patch. -- Michal Hocko SUSE Labs
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