From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ralph Campbell Subject: Re: [PATCH 9/9] mm: remove the MIGRATE_PFN_WRITE flag Date: Mon, 29 Jul 2019 16:42:01 -0700 Message-ID: <1f0ef337-6ca5-54fa-e627-41a46be73f2b@nvidia.com> References: <20190729142843.22320-1-hch@lst.de> <20190729142843.22320-10-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190729142843.22320-10-hch@lst.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jason Gunthorpe , Ben Skeggs Cc: Bharata B Rao , Andrew Morton , linux-mm@kvack.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org List-Id: dri-devel@lists.freedesktop.org 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.