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[209.132.183.28]) by mx.google.com with ESMTPS id f12si41221498qvf.37.2019.07.29.16.46.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Jul 2019 16:46:19 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 91FA74627A; Mon, 29 Jul 2019 23:46:18 +0000 (UTC) Received: from redhat.com (ovpn-112-31.rdu2.redhat.com [10.10.112.31]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4798C19C58; Mon, 29 Jul 2019 23:46:14 +0000 (UTC) Date: Mon, 29 Jul 2019 19:46:11 -0400 From: Jerome Glisse To: Ralph Campbell Cc: Christoph Hellwig , Jason Gunthorpe , Ben Skeggs , Bharata B Rao , Andrew Morton , linux-mm@kvack.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 9/9] mm: remove the MIGRATE_PFN_WRITE flag Message-ID: <20190729234611.GC7171@redhat.com> References: <20190729142843.22320-1-hch@lst.de> <20190729142843.22320-10-hch@lst.de> <1f0ef337-6ca5-54fa-e627-41a46be73f2b@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1f0ef337-6ca5-54fa-e627-41a46be73f2b@nvidia.com> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 29 Jul 2019 23:46:18 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 29, 2019 at 04:42:01PM -0700, Ralph Campbell wrote: > > On 7/29/19 7:28 AM, Christoph Hellwig wrote: > > The MIGRATE_PFN_WRITE is only used locally in migrate_vma_collect_pmd, > > where it can be replaced with a simple boolean local variable. > > > > Signed-off-by: Christoph Hellwig > > Reviewed-by: Ralph Campbell > > > --- > > include/linux/migrate.h | 1 - > > mm/migrate.c | 9 +++++---- > > 2 files changed, 5 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/migrate.h b/include/linux/migrate.h > > index 8b46cfdb1a0e..ba74ef5a7702 100644 > > --- a/include/linux/migrate.h > > +++ b/include/linux/migrate.h > > @@ -165,7 +165,6 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm, > > #define MIGRATE_PFN_VALID (1UL << 0) > > #define MIGRATE_PFN_MIGRATE (1UL << 1) > > #define MIGRATE_PFN_LOCKED (1UL << 2) > > -#define MIGRATE_PFN_WRITE (1UL << 3) > > #define MIGRATE_PFN_SHIFT 6 > > static inline struct page *migrate_pfn_to_page(unsigned long mpfn) > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 74735256e260..724f92dcc31b 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -2212,6 +2212,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > > unsigned long mpfn, pfn; > > struct page *page; > > swp_entry_t entry; > > + bool writable = false; > > pte_t pte; > > pte = *ptep; > > @@ -2240,7 +2241,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > > mpfn = migrate_pfn(page_to_pfn(page)) | > > MIGRATE_PFN_MIGRATE; > > if (is_write_device_private_entry(entry)) > > - mpfn |= MIGRATE_PFN_WRITE; > > + writable = true; > > } else { > > if (is_zero_pfn(pfn)) { > > mpfn = MIGRATE_PFN_MIGRATE; > > @@ -2250,7 +2251,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > > } > > page = vm_normal_page(migrate->vma, addr, pte); > > mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; > > - mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0; > > + if (pte_write(pte)) > > + writable = true; > > } > > /* FIXME support THP */ > > @@ -2284,8 +2286,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > > ptep_get_and_clear(mm, addr, ptep); > > /* Setup special migration page table entry */ > > - entry = make_migration_entry(page, mpfn & > > - MIGRATE_PFN_WRITE); > > + entry = make_migration_entry(page, writable); > > swp_pte = swp_entry_to_pte(entry); > > if (pte_soft_dirty(pte)) > > swp_pte = pte_swp_mksoft_dirty(swp_pte); > > > > MIGRATE_PFN_WRITE may mot being used but that seems like a bug to me. > If a page is migrated to device memory, it could be mapped at the same > time to avoid a device page fault but it would need the flag to know > whether to map it RW or RO. But I suppose that could be inferred from > the vma->vm_flags. It is a bug that it is not being use right now. I will have to dig my git repo to see when that got kill. Will look into it once i get back. The vma->vm_flags is of no use here. A page can be write protected inside a writable vma for various reasons. Cheers, Jérôme