From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f49.google.com (mail-pa0-f49.google.com [209.85.220.49]) by kanga.kvack.org (Postfix) with ESMTP id 345B56B008C for ; Fri, 24 Oct 2014 00:00:20 -0400 (EDT) Received: by mail-pa0-f49.google.com with SMTP id hz1so360130pad.36 for ; Thu, 23 Oct 2014 21:00:19 -0700 (PDT) Received: from heian.cn.fujitsu.com ([59.151.112.132]) by mx.google.com with ESMTP id c4si3088961pds.247.2014.10.23.21.00.18 for ; Thu, 23 Oct 2014 21:00:19 -0700 (PDT) Message-ID: <5449C8A6.9080403@cn.fujitsu.com> Date: Fri, 24 Oct 2014 11:33:58 +0800 From: Lai Jiangshan MIME-Version: 1.0 Subject: Re: [RFC][PATCH 4/6] SRCU free VMAs References: <20141020215633.717315139@infradead.org> <20141020222841.419869904@infradead.org> <5448D515.90006@cn.fujitsu.com> <20141023110346.GP21513@worktop.programming.kicks-ass.net> In-Reply-To: <20141023110346.GP21513@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: torvalds@linux-foundation.org, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, akpm@linux-foundation.org, riel@redhat.com, mgorman@suse.de, oleg@redhat.com, mingo@redhat.com, minchan@kernel.org, kamezawa.hiroyu@jp.fujitsu.com, viro@zeniv.linux.org.uk, dave@stgolabs.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org On 10/23/2014 07:03 PM, Peter Zijlstra wrote: > On Thu, Oct 23, 2014 at 06:14:45PM +0800, Lai Jiangshan wrote: >> >>> >>> +struct vm_area_struct *find_vma_srcu(struct mm_struct *mm, unsigned long addr) >>> +{ >>> + struct vm_area_struct *vma; >>> + unsigned int seq; >>> + >>> + WARN_ON_ONCE(!srcu_read_lock_held(&vma_srcu)); >>> + >>> + do { >>> + seq = read_seqbegin(&mm->mm_seq); >>> + vma = __find_vma(mm, addr); >> >> will the __find_vma() loops for ever due to the rotations in the RBtree? > > No, a rotation takes a tree and generates a tree, furthermore the > rotation has a fairly strict fwd progress guarantee seeing how its now > done with preemption disabled. I can't get the magic. __find_vma is visiting vma_a, vma_a is rotated to near the top due to multiple updates to the mm. __find_vma is visiting down to near the bottom, vma_b. now vma_b is rotated up to near the top again. __find_vma is visiting down to near the bottom, vma_c. now vma_c is rotated up to near the top again. ... > > Therefore, even if we're in a node that's being rotated up, we can only > 'loop' for as long as it takes for the new pointer stores to become > visible on our CPU. > > Thus we have a tree descent termination guarantee. > . > -- 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