From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 0E2986B004D for ; Fri, 9 Dec 2011 15:24:08 -0500 (EST) Date: Fri, 9 Dec 2011 12:24:06 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: simplify find_vma_prev Message-Id: <20111209122406.11f9e31a.akpm@linux-foundation.org> In-Reply-To: <1323461345-12805-1-git-send-email-kosaki.motohiro@gmail.com> References: <1323461345-12805-1-git-send-email-kosaki.motohiro@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: kosaki.motohiro@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, KOSAKI Motohiro , Hugh Dickins , Peter Zijlstra , Shaohua Li On Fri, 9 Dec 2011 15:09:04 -0500 kosaki.motohiro@gmail.com wrote: > From: KOSAKI Motohiro > > commit 297c5eee37 (mm: make the vma list be doubly linked) added > vm_prev member into vm_area_struct. Therefore we can simplify > find_vma_prev() by using it. Also, this change help to imporove > page fault performance becuase it has strong locality of reference. > > Signed-off-by: KOSAKI Motohiro > --- > mm/mmap.c | 34 ++++++---------------------------- > 1 files changed, 6 insertions(+), 28 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index eae90af..955750c 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1605,37 +1605,15 @@ EXPORT_SYMBOL(find_vma); > > /* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */ > struct vm_area_struct * > -find_vma_prev(struct mm_struct *mm, unsigned long addr, > - struct vm_area_struct **pprev) > +find_vma_prev(struct mm_struct *mm, unsigned long addr, struct vm_area_struct **pprev) > { > - struct vm_area_struct *vma = NULL, *prev = NULL; > - struct rb_node *rb_node; > - if (!mm) > - goto out; > - > - /* Guard against addr being lower than the first VMA */ > - vma = mm->mmap; > - > - /* Go through the RB tree quickly. */ > - rb_node = mm->mm_rb.rb_node; > - > - while (rb_node) { > - struct vm_area_struct *vma_tmp; > - vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb); > + struct vm_area_struct *vma; > > - if (addr < vma_tmp->vm_end) { > - rb_node = rb_node->rb_left; > - } else { > - prev = vma_tmp; > - if (!prev->vm_next || (addr < prev->vm_next->vm_end)) > - break; > - rb_node = rb_node->rb_right; > - } > - } > + vma = find_vma(mm, addr); > + if (vma) > + *pprev = vma->vm_prev; > > -out: > - *pprev = prev; > - return prev ? prev->vm_next : vma; > + return vma; > } This changes the (undocumented, naturally) interface in disturbing ways. Currently, *pprev will always be written to. With this change, *pprev will only be written to if find_vma_prev() returns non-NULL. Looking through the code, this is mostly benign. But it will cause the CONFIG_STACK_GROWSUP version of find_extend_vma() to use an uninitialised stack slot in ways which surely will crash the kernel. So please have a think about that and fix it up. And please add documentation for find_vma_prev()'s interface so we don't break it next time. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org