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[209.132.180.67]) by mx.google.com with ESMTP id j3si4723013edh.14.2019.10.31.11.36.32; Thu, 31 Oct 2019 11:36:56 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729345AbfJaSfv (ORCPT + 99 others); Thu, 31 Oct 2019 14:35:51 -0400 Received: from mga12.intel.com ([192.55.52.136]:38691 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729027AbfJaSfu (ORCPT ); Thu, 31 Oct 2019 14:35:50 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Oct 2019 11:35:49 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,252,1569308400"; d="scan'208";a="230963750" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by fmsmga002.fm.intel.com with ESMTP; 31 Oct 2019 11:35:49 -0700 Date: Thu, 31 Oct 2019 11:35:49 -0700 From: Ira Weiny To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML , Christoph Hellwig , "Aneesh Kumar K . V" Subject: Re: [PATCH 02/19] mm/gup: factor out duplicate code from four routines Message-ID: <20191031183549.GC14771@iweiny-DESK2.sc.intel.com> References: <20191030224930.3990755-1-jhubbard@nvidia.com> <20191030224930.3990755-3-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030224930.3990755-3-jhubbard@nvidia.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 30, 2019 at 03:49:13PM -0700, John Hubbard wrote: > There are four locations in gup.c that have a fair amount of code > duplication. This means that changing one requires making the same > changes in four places, not to mention reading the same code four > times, and wondering if there are subtle differences. > > Factor out the common code into static functions, thus reducing the > overall line count and the code's complexity. > > Also, take the opportunity to slightly improve the efficiency of the > error cases, by doing a mass subtraction of the refcount, surrounded > by get_page()/put_page(). > > Also, further simplify (slightly), by waiting until the the successful > end of each routine, to increment *nr. Overall it seems like a pretty good clean up. It did take a bit of review but I _think_ it is correct. A couple of comments below. > > Cc: Christoph Hellwig > Cc: Aneesh Kumar K.V > Signed-off-by: John Hubbard > --- > mm/gup.c | 113 ++++++++++++++++++++++--------------------------------- > 1 file changed, 46 insertions(+), 67 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 85caf76b3012..8fb0d9cdfaf5 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1969,6 +1969,35 @@ static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr, > } > #endif > > +static int __record_subpages(struct page *page, unsigned long addr, > + unsigned long end, struct page **pages, int nr) > +{ > + int nr_recorded_pages = 0; > + > + do { > + pages[nr] = page; > + nr++; > + page++; > + nr_recorded_pages++; > + } while (addr += PAGE_SIZE, addr != end); > + return nr_recorded_pages; > +} > + > +static void __remove_refs_from_head(struct page *page, int refs) > +{ > + /* Do a get_page() first, in case refs == page->_refcount */ > + get_page(page); > + page_ref_sub(page, refs); > + put_page(page); > +} I wonder if this is better implemented as "put_compound_head()"? To match the try_get_compound_head() call below? > + > +static int __huge_pt_done(struct page *head, int nr_recorded_pages, int *nr) > +{ > + *nr += nr_recorded_pages; > + SetPageReferenced(head); > + return 1; When will this return anything but 1? Ira > +} > + > #ifdef CONFIG_ARCH_HAS_HUGEPD > static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end, > unsigned long sz) > @@ -1998,34 +2027,19 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, > /* hugepages are never "special" */ > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > > - refs = 0; > head = pte_page(pte); > - > page = head + ((addr & (sz-1)) >> PAGE_SHIFT); > - do { > - VM_BUG_ON(compound_head(page) != head); > - pages[*nr] = page; > - (*nr)++; > - page++; > - refs++; > - } while (addr += PAGE_SIZE, addr != end); > + refs = __record_subpages(page, addr, end, pages, *nr); > > head = try_get_compound_head(head, refs); > - if (!head) { > - *nr -= refs; > + if (!head) > return 0; > - } > > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > - /* Could be optimized better */ > - *nr -= refs; > - while (refs--) > - put_page(head); > + __remove_refs_from_head(head, refs); > return 0; > } > - > - SetPageReferenced(head); > - return 1; > + return __huge_pt_done(head, refs, nr); > } > > static int gup_huge_pd(hugepd_t hugepd, unsigned long addr, > @@ -2071,30 +2085,18 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, > pages, nr); > } > > - refs = 0; > page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > - do { > - pages[*nr] = page; > - (*nr)++; > - page++; > - refs++; > - } while (addr += PAGE_SIZE, addr != end); > + refs = __record_subpages(page, addr, end, pages, *nr); > > head = try_get_compound_head(pmd_page(orig), refs); > - if (!head) { > - *nr -= refs; > + if (!head) > return 0; > - } > > if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { > - *nr -= refs; > - while (refs--) > - put_page(head); > + __remove_refs_from_head(head, refs); > return 0; > } > - > - SetPageReferenced(head); > - return 1; > + return __huge_pt_done(head, refs, nr); > } > > static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, > @@ -2114,30 +2116,18 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, > pages, nr); > } > > - refs = 0; > page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > - do { > - pages[*nr] = page; > - (*nr)++; > - page++; > - refs++; > - } while (addr += PAGE_SIZE, addr != end); > + refs = __record_subpages(page, addr, end, pages, *nr); > > head = try_get_compound_head(pud_page(orig), refs); > - if (!head) { > - *nr -= refs; > + if (!head) > return 0; > - } > > if (unlikely(pud_val(orig) != pud_val(*pudp))) { > - *nr -= refs; > - while (refs--) > - put_page(head); > + __remove_refs_from_head(head, refs); > return 0; > } > - > - SetPageReferenced(head); > - return 1; > + return __huge_pt_done(head, refs, nr); > } > > static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, > @@ -2151,30 +2141,19 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, > return 0; > > BUILD_BUG_ON(pgd_devmap(orig)); > - refs = 0; > + > page = pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); > - do { > - pages[*nr] = page; > - (*nr)++; > - page++; > - refs++; > - } while (addr += PAGE_SIZE, addr != end); > + refs = __record_subpages(page, addr, end, pages, *nr); > > head = try_get_compound_head(pgd_page(orig), refs); > - if (!head) { > - *nr -= refs; > + if (!head) > return 0; > - } > > if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { > - *nr -= refs; > - while (refs--) > - put_page(head); > + __remove_refs_from_head(head, refs); > return 0; > } > - > - SetPageReferenced(head); > - return 1; > + return __huge_pt_done(head, refs, nr); > } > > static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, > -- > 2.23.0 > >