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Date: Wed, 10 Feb 2016 12:50:12 +0200 From: "Kirill A. Shutemov" <kirill@...temov.name> To: Vineet Gupta <Vineet.Gupta1@...opsys.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>, Andrea Arcangeli <aarcange@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, stable@...r.kernel.org, linux-snps-arc@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH] mm,thp: khugepaged: call pte flush at the time of collapse On Wed, Feb 10, 2016 at 10:26:15AM +0530, Vineet Gupta wrote: > This showed up on ARC when running LMBench bw_mem tests as > Overlapping TLB Machine Check Exception triggered due to STLB entry > (2M pages) overlapping some NTLB entry (regular 8K page). > > bw_mem 2m touches a large chunk of vaddr creating NTLB entries. > In the interim khugepaged kicks in, collapsing the contiguous ptes into > a single pmd. pmdp_collapse_flush()->flush_pmd_tlb_range() is called to > flush out NTLB entries for the ptes. This for ARC (by design) can only > shootdown STLB entries (for pmd). The stray NTLB entries cause the overlap > with the subsequent STLB entry for collapsed page. > So make pmdp_collapse_flush() call pte flush interface not pmd flush. > > Note that originally all thp flush call sites in generic code called > flush_tlb_range() leaving it to architecture to implement the flush for > pte and/or pmd. Commit 12ebc1581ad11454 changed this by calling a new > opt-in API flush_pmd_tlb_range() which made the semantics more explicit > but failed to distinguish the pte vs pmd flush in generic code, which is > what this patch fixes. > > Note that ARC can fixed w/o touching the generic pmdp_collapse_flush() > by defining a ARC version, but that defeats the purpose of generic > version, plus sementically this is the right thing to do. > > Fixes STAR 9000961194: LMBench on AXS103 triggering duplicate TLB > exceptions with super pages > > Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> > Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com> > Cc: Andrea Arcangeli <aarcange@...hat.com> > Cc: Andrew Morton <akpm@...ux-foundation.org> > Cc: <stable@...r.kernel.org> #4.4 > Cc: <linux-snps-arc@...ts.infradead.org> > Cc: linux-kernel@...r.kernel.org > Cc: linux-mm@...ck.org > Fixes: 12ebc1581ad11454 ("mm,thp: introduce flush_pmd_tlb_range") > Signed-off-by: Vineet Gupta <vgupta@...opsys.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> -- Kirill A. Shutemov
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