From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f46.google.com (mail-pa0-f46.google.com [209.85.220.46]) by kanga.kvack.org (Postfix) with ESMTP id 6B5A46B0035 for ; Wed, 13 Aug 2014 17:08:03 -0400 (EDT) Received: by mail-pa0-f46.google.com with SMTP id lj1so351888pab.33 for ; Wed, 13 Aug 2014 14:08:03 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id uj2si2352484pbc.60.2014.08.13.14.08.02 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Aug 2014 14:08:02 -0700 (PDT) Date: Wed, 13 Aug 2014 14:08:00 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: introduce for_each_vma helpers Message-Id: <20140813140800.df0310a05e5fad6ed6b55886@linux-foundation.org> In-Reply-To: <1407887208.2695.9.camel@buesod1.americas.hpqcorp.net> References: <1407865523.2633.3.camel@buesod1.americas.hpqcorp.net> <20140812215213.GB17497@node.dhcp.inet.fi> <1407887208.2695.9.camel@buesod1.americas.hpqcorp.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Davidlohr Bueso Cc: "Kirill A. Shutemov" , Martin Schwidefsky , Heiko Carstens , "James E.J. Bottomley" , Helge Deller , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Robert Richter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, aswin@hp.com On Tue, 12 Aug 2014 16:46:48 -0700 Davidlohr Bueso wrote: > On Wed, 2014-08-13 at 00:52 +0300, Kirill A. Shutemov wrote: > > On Tue, Aug 12, 2014 at 10:45:23AM -0700, Davidlohr Bueso wrote: > > > The most common way of iterating through the list of vmas, is via: > > > for (vma = mm->mmap; vma; vma = vma->vm_next) > > > > > > This patch replaces this logic with a new for_each_vma(vma) helper, > > > which 1) encapsulates this logic, and 2) make it easier to read. > > > > Why does it need to be encapsulated? > > Do you have problem with reading plain for()? > > > > Your for_each_vma(vma) assumes "mm" from the scope. This can be confusing > > for reader: whether it uses "mm" from the scope or "current->mm". This > > will lead to very hard to find bug one day. > > I think its fairly obvious to see where the mm is coming from -- the > helpers *do not* necessarily use current, it uses whatever mm was > already there in the first place. I have not changed anything related to > this from the callers. It is a bit of a hand-grenade for those (rare) situations where code is dealing with other-tasks-mm. It's simple enough to add an `mm' arg? > The only related change I can think of, is for some callers that do: > > for (vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) > > So we just add a local mm from current->mm and replace the for() with > for_each_vma(). I don't see anything particularly ambiguous with that. Adding a local to support a macro which secretly uses that local is pretty nasty. Overall, I'm not really sure that - for (vma = mm->mmap; vma; vma = vma->vm_next) { + for_each_vma(mm, vma) { is much of an improvement. I'll wait to see what others think... -- 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