From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk1-f176.google.com (mail-qk1-f176.google.com [209.85.222.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2C23E3FC2 for ; Fri, 27 Aug 2021 16:25:54 +0000 (UTC) Received: by mail-qk1-f176.google.com with SMTP id a66so7813304qkc.1 for ; Fri, 27 Aug 2021 09:25:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=6UXnHWuhKzdu/oSUtPKlkCaxdX6yM9oY2hFSeSoJKFk=; b=MBKXEHmhUOxNCtbOpmWHL1bTGVLftX21Bc+ceHSSen0risnXXb2gF7W5nRFloJm1Mj LDmuW+oGvWNmNdbSmr9Cyobr4WdbmKIzdaO5fGSoOW0DaSgkigWZ0xCJHZxmnVFI+Key Mq7r/RuCT6tUX2SivKPGa0TiRSpYQ8oc4ipBmMJ4Rhzw4uFfPDS7uN9mRHzsjHBv27oX GfitSLhjYpVh7N8xsl0zmEUB9zuYyadeA1M+Tt4dCzVbAl40w+Q6gogENMI6RBkTAlU5 xwM2imVS4i1d0tQS4T6Y+c9Giks7NFwLPOyzfEZdEsN4sq8t/24OeII55CeOMijLLvYe QsPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=6UXnHWuhKzdu/oSUtPKlkCaxdX6yM9oY2hFSeSoJKFk=; b=HPEERyEXsQO/nbEvnZ/30CxruS4Dtm4NqUVrxhnVTK8HmIWsKr1sY1rAPOaPcCUv1O SYROwSDeBWq41XTfObc2THXuHV4Itb5Hj5zdKUCvnKXjLj2+CzjeVcdxyxSN+Og7Yu/B iHzTg8yqLYyKlY22jMd06NksSyy36A9X6WViyYu3QZKzIaXX6b05WQuGECEUo0784zpr 9o/Zgytqrqv9waylVIVsiSjGwQM2yw0vSWPVKcRLIFb8xbRCP+MfDO8d59zfZSMBvVhV G2LFPSFnJKEwOdgmiEzzW3w2hNFD7/Enxe75iB64+QKTXhgs90ALBE92wuZcfJuPPTC/ 8KEg== X-Gm-Message-State: AOAM533eJUkkrpXLMHHPFJI1/Tn6WGOyDfHEktCeJlhm/KnsV4+Kqg7u PU05aNY7Q3LHimqr6HIHJLjhiA== X-Google-Smtp-Source: ABdhPJzxYeFXuTHbMzxeNMezaNcAi/eCldZjs5Wu+hIW4J1zkBCfYUFDgsaQw27Tcf1kMf3qE5UBQg== X-Received: by 2002:a37:a9d2:: with SMTP id s201mr9435593qke.132.1630081553947; Fri, 27 Aug 2021 09:25:53 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-142-162-113-129.dhcp-dynamic.fibreop.ns.bellaliant.net. [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> Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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> 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