From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id 1C6906B028B for ; Tue, 16 Jan 2018 14:35:12 -0500 (EST) Received: by mail-wr0-f200.google.com with SMTP id 31so6543844wru.0 for ; Tue, 16 Jan 2018 11:35:12 -0800 (PST) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id c21si19974wrc.92.2018.01.16.11.35.10 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 16 Jan 2018 11:35:10 -0800 (PST) Date: Tue, 16 Jan 2018 20:34:59 +0100 (CET) From: Thomas Gleixner Subject: Re: [PATCH 07/16] x86/mm: Move two more functions from pgtable_64.h to pgtable.h In-Reply-To: <20180116191105.GC28161@8bytes.org> Message-ID: References: <1516120619-1159-1-git-send-email-joro@8bytes.org> <1516120619-1159-8-git-send-email-joro@8bytes.org> <727a7eba-41a0-d5bb-df54-8e58b33fde76@intel.com> <20180116191105.GC28161@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Joerg Roedel Cc: Dave Hansen , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andy Lutomirski , Josh Poimboeuf , Juergen Gross , Peter Zijlstra , Borislav Petkov , Jiri Kosina , Boris Ostrovsky , Brian Gerst , David Laight , Denys Vlasenko , Eduardo Valentin , Greg KH , Will Deacon , aliguori@amazon.com, daniel.gruss@iaik.tugraz.at, hughd@google.com, keescook@google.com, Andrea Arcangeli , Waiman Long , jroedel@suse.de On Tue, 16 Jan 2018, Joerg Roedel wrote: > On Tue, Jan 16, 2018 at 10:03:09AM -0800, Dave Hansen wrote: > > On 01/16/2018 08:36 AM, Joerg Roedel wrote: > > > + return (((ptr & ~PAGE_MASK) / sizeof(pgd_t)) < KERNEL_PGD_BOUNDARY); > > > +} > > > > One of the reasons to implement it the other way: > > > > - return (ptr & ~PAGE_MASK) < (PAGE_SIZE / 2); > > > > is that the compiler can do this all quickly. KERNEL_PGD_BOUNDARY > > depends on PAGE_OFFSET which depends on a variable. IOW, the compiler > > can't do it. > > > > How much worse is the code that this generates? > > I havn't looked at the actual code this generates, but the > (PAGE_SIZE / 2) comparison doesn't work on 32 bit where the address > space is not always evenly split. I'll look into a better way to check > this. It should be trivial enough to do return (ptr & ~PAGE_MASK) < PGD_SPLIT_SIZE); and define it PAGE_SIZE/2 for 64bit and for PAE make it depend on the configured address space split. Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org