Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758851AbYARKPx (ORCPT ); Fri, 18 Jan 2008 05:15:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754792AbYARKPq (ORCPT ); Fri, 18 Jan 2008 05:15:46 -0500 Received: from viefep18-int.chello.at ([213.46.255.22]:48294 "EHLO viefep16-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751004AbYARKPp (ORCPT ); Fri, 18 Jan 2008 05:15:45 -0500 X-SourceIP: 80.56.237.116 Subject: Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped files From: Peter Zijlstra To: Miklos Szeredi Cc: salikhmetov@gmail.com, linux-mm@kvack.org, jakob@unthought.net, linux-kernel@vger.kernel.org, valdis.kletnieks@vt.edu, riel@redhat.com, ksm@42.dk, staubach@redhat.com, jesper.juhl@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, protasnb@gmail.com, r.e.wolff@bitwizard.nl, hidave.darkstar@gmail.com, hch@infradead.org In-Reply-To: References: <12006091182260-git-send-email-salikhmetov@gmail.com> <12006091211208-git-send-email-salikhmetov@gmail.com> Content-Type: text/plain Date: Fri, 18 Jan 2008 11:15:36 +0100 Message-Id: <1200651337.5920.9.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.21.5 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2125 Lines: 69 On Fri, 2008-01-18 at 10:51 +0100, Miklos Szeredi wrote: > > diff --git a/mm/msync.c b/mm/msync.c > > index a4de868..a49af28 100644 > > --- a/mm/msync.c > > +++ b/mm/msync.c > > @@ -13,11 +13,33 @@ > > #include > > > > /* > > + * Scan the PTEs for pages belonging to the VMA and mark them read-only. > > + * It will force a pagefault on the next write access. > > + */ > > +static void vma_wrprotect(struct vm_area_struct *vma) > > +{ > > + unsigned long addr; > > + > > + for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) { > > + spinlock_t *ptl; > > + pgd_t *pgd = pgd_offset(vma->vm_mm, addr); > > + pud_t *pud = pud_offset(pgd, addr); > > + pmd_t *pmd = pmd_offset(pud, addr); > > + pte_t *pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > > + > > + if (pte_dirty(*pte) && pte_write(*pte)) > > + *pte = pte_wrprotect(*pte); > > + pte_unmap_unlock(pte, ptl); > > + } > > +} > > What about ram based filesystems? They don't start out with read-only > pte's, so I think they don't want them read-protected now either. > Unless this is essential for correct mtime/ctime accounting on these > filesystems (I don't think it really is). But then the mapping should > start out read-only as well, otherwise the time update will only work > after an msync(MS_ASYNC). page_mkclean() has all the needed logic for this, it also walks the rmap and cleans out all other users, which I think is needed too for consistencies sake: Process A Process B mmap(foo.txt) mmap(foo.txt) dirty page dirty page msync(MS_ASYNC) dirty page msync(MS_ASYNC) <--- now what?! So what I would suggest is using the page table walkers from mm, and walks the page range, obtain the page using vm_normal_page() and call page_mkclean(). (Oh, and ensure you don't nest the pte lock :-) All in all, that sounds rather expensive.. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/