From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id C95026B004A for ; Tue, 14 Sep 2010 07:34:03 -0400 (EDT) Date: Tue, 14 Sep 2010 13:33:59 +0200 (CEST) From: Richard Guenther Subject: Re: [PATCH] After swapout/swapin private dirty mappings become clean In-Reply-To: <201009141640.55650.knikanth@suse.de> Message-ID: References: <201009141640.55650.knikanth@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Nikanth Karthikesan Cc: linux-mm@kvack.org, Andrew Morton , balbir@linux.vnet.ibm.com, Michael Matz , Matt Mackall , linux-kernel@vger.kernel.org List-ID: On Tue, 14 Sep 2010, Nikanth Karthikesan wrote: > /proc/$pid/smaps broken: After swapout/swapin private dirty mappings become > clean. > > When a page with private file mapping becomes dirty, the vma will be in both > i_mmap tree and anon_vma list. The /proc/$pid/smaps will account these pages > as dirty and backed by the file. > > But when those dirty pages gets swapped out, and when they are read back from > swap, they would be marked as clean, as it should be, as they are part of swap > cache now. > > But the /proc/$pid/smaps would report the vma as a mapping of a file and it is > clean. The pages are actually in same state i.e., dirty with respect to file > still, but which was once reported as dirty is now being reported as clean to > user-space. > > This confuses tools like gdb which uses this information. Those tools think > that those pages were never modified and it creates problem when they create > dumps. > > The file mapping of the vma also cannot be broken as pages never read earlier, > will still have to come from the file. Just that those dirty pages have become > clean anonymous pages. > > During swaping in, restoring the exact state as dirty file-backed pages before > swapout would be useless, as there in no real bug. Breaking the vma with only > anonymous pages as seperate vmas unnecessary may not be a good thing as well. > So let us just export the information that a file-backed vma has anonymous > dirty pages. > > Export this information in smaps by prepending file-names with "[anon]+", when > some of the pages in a file backed vma become anonymous. For the sake of not breaking existing tools I'd prefer appending " [anon]" instead. Though a much simpler thing would be to account the clean anon pages as Private_Dirty (with respect to the backing file displayed). Anonymous vmas in /proc/smaps seem to contain Private_Dirty pages as well. So I still don't understand why this isn't just an accounting bug. Thanks, Richard. > Signed-off-by: Nikanth Karthikesan > > --- > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 439fc1f..68f9806 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -242,6 +242,8 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma) > */ > if (file) { > pad_len_spaces(m, len); > + if (vma->anon_vma) > + seq_puts(m, "[anon]+"); > seq_path(m, &file->f_path, "\n"); > } else { > const char *name = arch_vma_name(vma); > > > -- Richard Guenther Novell / SUSE Labs SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746 - GF: Markus Rex -- 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