From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754856AbZBDCMx (ORCPT ); Tue, 3 Feb 2009 21:12:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752254AbZBDCMp (ORCPT ); Tue, 3 Feb 2009 21:12:45 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:48992 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752178AbZBDCMo (ORCPT ); Tue, 3 Feb 2009 21:12:44 -0500 From: KOSAKI Motohiro To: MinChan Kim Subject: Re: [PATCH v2] fix mlocked page counter mistmatch Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton , linux mm , linux kernel , Nick Piggin , Rik van Riel In-Reply-To: <20090203234408.GA6212@barrios-desktop> References: <2f11576a0902030844l64c25496sa5f2892bbb04e47c@mail.gmail.com> <20090203234408.GA6212@barrios-desktop> Message-Id: <20090204103648.ECAF.KOSAKI.MOTOHIRO@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.42 [ja] Date: Wed, 4 Feb 2009 11:12:37 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Wed, Feb 04, 2009 at 01:44:52AM +0900, KOSAKI Motohiro wrote: > > Hi MinChan, > > > > I'm confusing now. > > Can you teach me? > > No problem. :) > > > > > > When I tested following program, I found that mlocked counter > > > is strange. > > > It couldn't free some mlocked pages of test program. > > > It is caused that try_to_unmap_file don't check real > > > page mapping in vmas. > > > > What meanining is "real" page mapping? > > What I mean is that if the page is mapped at the vma, > I call it's "real" page mapping. > I explain it more detaily below. > > > > > > > > That's because goal of address_space for file is to find all processes > > > into which the file's specific interval is mapped. > > > What I mean is that it's not related page but file's interval. > > > > hmmm. No. > > I ran your reproduce program. > > > > two vma pointing the same page cause this leaking. > > I don't think so. Please confirm by actual machine and kernel. I confirmed by printk debugging. > > iow, any library have .text and .data segment. then the tail of .text > > and the head of .data vma point the same page. > > its page was leaked. > > > > > > > Even if the page isn't really mapping at the vma, it returns > > > SWAP_MLOCK since the vma have VM_LOCKED, then calls > > > try_to_mlock_page. After all, mlocked counter is increased again. > > > > > > COWed anon page in a file-backed vma could be a such case. > > > This patch resolves it. > > > > What meaning is "anon page in a file-backed"? > > As far as I know, if cow happend on private mapping page, new page is > > treated truth anon. > > > > vm_area_struct's annotation can explain about your question. > > struct vm_area_struct { > struct mm_struct * vm_mm; /* The address space we belong to. */ > .... > .... > /* > * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma > * list, after a COW of one of the file pages. A MAP_SHARED vma > * can only be in the i_mmap tree. An anonymous MAP_PRIVATE, stack > * or brk vma (with NULL file) can only be in an anon_vma list. > */ > struct list_head anon_vma_node; /* Serialized by anon_vma->lock */ > struct anon_vma *anon_vma; /* Serialized by page_table_lock */ > .... > .... > } > > Let us call it anon page in a file-backed. > In this case, the new page is mapped at the vma. > the vma don't include old page any more but i_mmap tree still have > the vma. hmhm. thanks. my understanding largely improvement. I agree page_check_address() checking is necessary. > So, the i_mmap tree can have the vma which don't include > the page if the one is anon page in a file-backed. > > This problem is caused by that. > Is it enough ? Could you please teach me why this issue doesn't happend on munlockall()? your scenario seems to don't depend on exit_mmap().