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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id j3sm4040399qti.4.2021.08.27.09.25.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Aug 2021 09:25:53 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mJefw-005jle-Kb; Fri, 27 Aug 2021 13:25:52 -0300 Date: Fri, 27 Aug 2021 13:25:52 -0300 From: Jason Gunthorpe To: Joao Martins Cc: linux-mm@kvack.org, Dan Williams , Vishal Verma , Dave Jiang , Naoya Horiguchi , Matthew Wilcox , John Hubbard , Jane Chu , Muchun Song , Mike Kravetz , Andrew Morton , Jonathan Corbet , Christoph Hellwig , nvdimm@lists.linux.dev, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 08/14] mm/gup: grab head page refcount once for group of subpages Message-ID: <20210827162552.GK1200268@ziepe.ca> References: <20210827145819.16471-1-joao.m.martins@oracle.com> <20210827145819.16471-9-joao.m.martins@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210827145819.16471-9-joao.m.martins@oracle.com> Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=MBKXEHmh; spf=pass (imf26.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.222.181 as permitted sender) smtp.mailfrom=jgg@ziepe.ca; dmarc=none X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9C55020019DE X-Stat-Signature: 3ujm47x4mto1bzw6kpy9rtsua3qzungy X-HE-Tag: 1630081554-624551 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 Fri, Aug 27, 2021 at 03:58:13PM +0100, Joao Martins wrote: > #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE) > static int __gup_device_huge(unsigned long pfn, unsigned long addr, > unsigned long end, unsigned int flags, > struct page **pages, int *nr) > { > - int nr_start = *nr; > + int refs, nr_start = *nr; > struct dev_pagemap *pgmap = NULL; > int ret = 1; > > do { > - struct page *page = pfn_to_page(pfn); > + struct page *head, *page = pfn_to_page(pfn); > + unsigned long next = addr + PAGE_SIZE; > > pgmap = get_dev_pagemap(pfn, pgmap); > if (unlikely(!pgmap)) { > @@ -2252,16 +2265,25 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr, > ret = 0; > break; > } > - SetPageReferenced(page); > - pages[*nr] = page; > - if (unlikely(!try_grab_page(page, flags))) { > - undo_dev_pagemap(nr, nr_start, flags, pages); > + > + head = compound_head(page); > + /* @end is assumed to be limited at most one compound page */ > + if (PageHead(head)) > + next = end; > + refs = record_subpages(page, addr, next, pages + *nr); > + > + SetPageReferenced(head); > + if (unlikely(!try_grab_compound_head(head, refs, flags))) { > + if (PageHead(head)) > + ClearPageReferenced(head); > + else > + undo_dev_pagemap(nr, nr_start, flags, pages); > ret = 0; > break; Why is this special cased for devmap? Shouldn't everything processing pud/pmds/etc use the same basic loop that is similar in idea to the 'for_each_compound_head' scheme in unpin_user_pages_dirty_lock()? Doesn't that work for all the special page type cases here? Jason