From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f198.google.com (mail-qk1-f198.google.com [209.85.222.198]) by kanga.kvack.org (Postfix) with ESMTP id 6FF1F6B027B for ; Fri, 12 Oct 2018 13:24:25 -0400 (EDT) Received: by mail-qk1-f198.google.com with SMTP id p128-v6so12424016qke.13 for ; Fri, 12 Oct 2018 10:24:25 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id g30-v6si1405465qtd.208.2018.10.12.10.24.24 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 12 Oct 2018 10:24:24 -0700 (PDT) Date: Fri, 12 Oct 2018 13:24:22 -0400 From: Andrea Arcangeli Subject: Re: [PATCH] mm/thp: fix call to mmu_notifier in set_pmd_migration_entry() Message-ID: <20181012172422.GA7395@redhat.com> References: <20181012160953.5841-1-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Zi Yan Cc: jglisse@redhat.com, linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Kirill A . Shutemov" , "H. Peter Anvin" , Anshuman Khandual , Dave Hansen , David Nellans , Ingo Molnar , Mel Gorman , Minchan Kim , Naoya Horiguchi , Thomas Gleixner , Vlastimil Babka , Michal Hocko Hello, On Fri, Oct 12, 2018 at 12:20:54PM -0400, Zi Yan wrote: > On 12 Oct 2018, at 12:09, jglisse@redhat.com wrote: > > > From: Jerome Glisse > > > > Inside set_pmd_migration_entry() we are holding page table locks and > > thus we can not sleep so we can not call invalidate_range_start/end() > > > > So remove call to mmu_notifier_invalidate_range_start/end() and add > > call to mmu_notifier_invalidate_range(). Note that we are already Why the call to mmu_notifier_invalidate_range if we're under range_start and followed by range_end? (it's not _range_only_end, if it was _range_only_end the above would be needed) > > calling mmu_notifier_invalidate_range_start/end() inside the function > > calling set_pmd_migration_entry() (see try_to_unmap_one()). > > > > Signed-off-by: Jerome Glisse > > Reported-by: Andrea Arcangeli > > Cc: Andrew Morton > > Cc: Greg Kroah-Hartman > > Cc: Zi Yan > > Cc: Kirill A. Shutemov > > Cc: "H. Peter Anvin" > > Cc: Anshuman Khandual > > Cc: Dave Hansen > > Cc: David Nellans > > Cc: Ingo Molnar > > Cc: Mel Gorman > > Cc: Minchan Kim > > Cc: Naoya Horiguchi > > Cc: Thomas Gleixner > > Cc: Vlastimil Babka > > Cc: Michal Hocko > > Cc: Andrea Arcangeli > > --- > > mm/huge_memory.c | 7 +------ > > 1 file changed, 1 insertion(+), 6 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 533f9b00147d..93cb80fe12cb 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2885,9 +2885,6 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > > if (!(pvmw->pmd && !pvmw->pte)) > > return; > > > > - mmu_notifier_invalidate_range_start(mm, address, > > - address + HPAGE_PMD_SIZE); > > - > > flush_cache_range(vma, address, address + HPAGE_PMD_SIZE); > > pmdval = *pvmw->pmd; > > pmdp_invalidate(vma, address, pvmw->pmd); > > @@ -2898,11 +2895,9 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > > if (pmd_soft_dirty(pmdval)) > > pmdswp = pmd_swp_mksoft_dirty(pmdswp); > > set_pmd_at(mm, address, pvmw->pmd, pmdswp); > > + mmu_notifier_invalidate_range(mm, address, address + HPAGE_PMD_SIZE); It's not obvious why it's needed, if it's needed maybe a comment can be added. > > page_remove_rmap(page, true); > > put_page(page); > > - > > - mmu_notifier_invalidate_range_end(mm, address, > > - address + HPAGE_PMD_SIZE); > > } > > > > void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new) > > -- > > 2.17.2 > > Yes, these are the redundant calls to mmu_notifier_invalidate_range_start/end() > in set_pmd_migration_entry(). Thanks for the patch. They're not just redundant, it's called in non blockable path with __mmu_notifier_invalidate_range_start(blockable=true). Furthermore mmu notifier API doesn't support nesting. KVM is actually robust against the nesting: kvm->mmu_notifier_count++; kvm->mmu_notifier_count--; and KVM is always fine with non blockable calls, but that's not universally true for all mmu notifier users. Thanks, Andrea