RE: [RFC] mm: change mm_advise_free to clear page dirty

["Wang, Yalin" <Yalin.Wang@sonymobile.com>]

> -----Original Message-----
> From: Minchan Kim [mailto:minchan.kim@gmail.com] On Behalf Of Minchan Kim
> Sent: Saturday, February 28, 2015 9:56 PM
> To: Wang, Yalin
> Cc: 'Michal Hocko'; Andrew Morton; linux-kernel@vger.kernel.org; linux-
> mm@kvack.org; Rik van Riel; Johannes Weiner; Mel Gorman; Shaohua Li
> Subject: Re: [RFC] mm: change mm_advise_free to clear page dirty
> 
> On Sat, Feb 28, 2015 at 10:11:13AM +0800, Wang, Yalin wrote:
> > > -----Original Message-----
> > > From: Michal Hocko [mailto:mstsxfx@gmail.com] On Behalf Of Michal Hocko
> > > Sent: Saturday, February 28, 2015 5:03 AM
> > > To: Wang, Yalin
> > > Cc: 'Minchan Kim'; Andrew Morton; linux-kernel@vger.kernel.org; linux-
> > > mm@kvack.org; Rik van Riel; Johannes Weiner; Mel Gorman; Shaohua Li
> > > Subject: Re: [RFC] mm: change mm_advise_free to clear page dirty
> > >
> > > On Fri 27-02-15 11:37:18, Wang, Yalin wrote:
> > > > This patch add ClearPageDirty() to clear AnonPage dirty flag,
> > > > the Anonpage mapcount must be 1, so that this page is only used by
> > > > the current process, not shared by other process like fork().
> > > > if not clear page dirty for this anon page, the page will never be
> > > > treated as freeable.
> > >
> > > Very well spotted! I haven't noticed that during the review.
> > >
> > > > Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
> > > > ---
> > > >  mm/madvise.c | 15 +++++----------
> > > >  1 file changed, 5 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > > index 6d0fcb8..257925a 100644
> > > > --- a/mm/madvise.c
> > > > +++ b/mm/madvise.c
> > > > @@ -297,22 +297,17 @@ static int madvise_free_pte_range(pmd_t *pmd,
> > > unsigned long addr,
> > > >  			continue;
> > > >
> > > >  		page = vm_normal_page(vma, addr, ptent);
> > > > -		if (!page)
> > > > +		if (!page || !PageAnon(page) || !trylock_page(page))
> > > >  			continue;
> > >
> > > PageAnon check seems to be redundant because we are not allowing
> > > MADV_FREE on any !anon private mappings AFAIR.
> > I only see this check:
> > /* MADV_FREE works for only anon vma at the moment */
> > 	if (vma->vm_file)
> > 		return -EINVAL;
> >
> > but for file private map, there are also AnonPage sometimes, do we need
> change
> > to like this:
> > 	if (vma->vm_flags & VM_SHARED)
> > 		return -EINVAL;
> 
> I couldn't understand your point. In this stage, we intentionally
> disabled madvise_free on file mapped area(AFAIRC, some guys tried
> it long time ago but it had many issues so dropped).
> So, how can file-private mmaped can reach this code?
> Could you elaborate it more about that why we need PageAnon check
> in here?
> 
I send a new patch:
[RFC V2] mm: change mm_advise_free to clear page dirty
Please have a look at it.
Thanks for your comments!