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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id w9si26742607pjv.67.2019.07.30.13.26.40 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 30 Jul 2019 13:26:40 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=g49i2KTA; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=yqx4UYcjP6KlxvhuVNhLTr763MCblrOaB2wNSqF59LA=; b=g49i2KTA4OHx/jCep6CF+UE9r FbNyMT6OL8WRSVCeidN56yT/Vcnr+AIESkseue6yVojwTnY1UR6PAJOxrBy4sr3HDTIRi+l9RDcGZ Zxkd90nko/NbaQWkWDn1KJTe1YrvC5tPRSqTEL2yj0XQOjPGZK7BVOdEj87Vmp+2lX6MvhTbp2gET McL2AVgDCkepYA4b+iNLOwOlBdSNVKtbfMVECMhhIBptp6Wfm6X2YfqHJMbVmPSdwK1M4z4s0NiKW tYKLicwNq6x63QmsrSVzSQjOyV9rbb9TTgkWuZ/RRylZgKeHw6tNJ+ovZ6o/IRhIPQeicMutGLcmb JEcyzV84w==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hsYhc-0007hT-DO; Tue, 30 Jul 2019 20:26:32 +0000 Date: Tue, 30 Jul 2019 13:26:32 -0700 From: Matthew Wilcox To: Song Liu Cc: William Kucharski , "ceph-devel@vger.kernel.org" , "linux-afs@lists.infradead.org" , "linux-btrfs@vger.kernel.org" , lkml , Linux-MM , Networking , Chris Mason , "David S. Miller" , David Sterba , Josef Bacik , Dave Hansen , Bob Kasten , Mike Kravetz , Chad Mynhier , "Kirill A. Shutemov" , Johannes Weiner , Dave Airlie , Vlastimil Babka , Keith Busch , Ralph Campbell , Steve Capper , Dave Chinner , Sean Christopherson , Hugh Dickins , Ilya Dryomov , Alexander Duyck , Thomas Gleixner , =?iso-8859-1?B?Suly9G1l?= Glisse , Amir Goldstein , Jason Gunthorpe , Michal Hocko , Jann Horn , David Howells , John Hubbard , Souptick Joarder , "john.hubbard@gmail.com" , Jan Kara , Andrey Konovalov , Arun KS , "Aneesh Kumar K.V" , Jeff Layton , Yangtao Li , Andrew Morton , Robin Murphy , Mike Rapoport , David Rientjes , Andrey Ryabinin , Yafang Shao , Huang Shijie , Yang Shi , Miklos Szeredi , Pavel Tatashin , Kirill Tkhai , Sage Weil , Ira Weiny , Dan Williams , "Darrick J. Wong" , Gao Xiang , Bartlomiej Zolnierkiewicz , Ross Zwisler , kbuild test robot Subject: Re: [PATCH v2 1/2] mm: Allow the page cache to allocate large pages Message-ID: <20190730202632.GC4700@bombadil.infradead.org> References: <20190729210933.18674-1-william.kucharski@oracle.com> <20190729210933.18674-2-william.kucharski@oracle.com> <443BA74D-9A8E-479B-9E63-4ACD6D6C0AF9@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <443BA74D-9A8E-479B-9E63-4ACD6D6C0AF9@fb.com> User-Agent: Mutt/1.11.4 (2019-03-13) 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 10:03:40PM +0000, Song Liu wrote: > > +/* If you add more flags, increment FGP_ORDER_SHIFT */ > > +#define FGP_ORDER_SHIFT 7 > > +#define FGP_PMD ((PMD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > > +#define FGP_PUD ((PUD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT) > > +#define fgp_get_order(fgp) ((fgp) >> FGP_ORDER_SHIFT) > > This looks like we want support order up to 25 (32 - 7). I guess we don't > need that many. How about we specify the highest order to support here? We can support all the way up to order 64 with just 6 bits, leaving 32 - 6 - 7 = 19 bits free. We haven't been adding FGP flags very quickly, so I doubt we'll need anything larger. > Also, fgp_flags is signed int, so we need to make sure fgp_flags is not > negative. If we ever get there, I expect people to convert the parameter from signed int to unsigned long.