Messages in this thread |  | | | From | Nikanth Karthikesan <> | | Subject | Re: [PATCH] After swapout/swapin private dirty mappings become clean | | Date | Tue, 14 Sep 2010 22:42:29 +0530 |
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On Tuesday 14 September 2010 17:03:59 Richard Guenther wrote: > 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. >
A filename might have it as suffix!
> Though a much simpler thing would be to account > the clean anon pages as Private_Dirty (with respect to the backing > file displayed).
Agreed.
> 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. >
anonymous pages can be dirty as well. Even these pages now marked as clean would be marked as dirty again, if they are re-dirtied.
Thanks Nikanth
> Thanks, > Richard. > > > Signed-off-by: Nikanth Karthikesan <knikanth@suse.de> > > > > --- > > > > 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); >
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