Re: + mm-reclaim-madv_free-pages.patch added to -mm tree

[Minchan Kim <minchan@kernel.org>]

On Mon, Mar 06, 2017 at 10:49:06AM -0500, Johannes Weiner wrote:
> On Mon, Mar 06, 2017 at 12:03:44PM +0900, Minchan Kim wrote:
> > On Fri, Mar 03, 2017 at 10:18:51AM -0500, Johannes Weiner wrote:
> > > On Fri, Mar 03, 2017 at 11:52:37AM +0900, Minchan Kim wrote:
> > > > On Tue, Feb 28, 2017 at 04:32:38PM -0800, akpm@linux-foundation.org wrote:
> > > > > 
> > > > > The patch titled
> > > > >      Subject: mm: reclaim MADV_FREE pages
> > > > > has been added to the -mm tree.  Its filename is
> > > > >      mm-reclaim-madv_free-pages.patch
> > > > > 
> > > > > This patch should soon appear at
> > > > >     http://ozlabs.org/~akpm/mmots/broken-out/mm-reclaim-madv_free-pages.patch
> > > > > and later at
> > > > >     http://ozlabs.org/~akpm/mmotm/broken-out/mm-reclaim-madv_free-pages.patch
> > > > > 
> > > > > Before you just go and hit "reply", please:
> > > > >    a) Consider who else should be cc'ed
> > > > >    b) Prefer to cc a suitable mailing list as well
> > > > >    c) Ideally: find the original patch on the mailing list and do a
> > > > >       reply-to-all to that, adding suitable additional cc's
> > > > > 
> > > > > *** Remember to use Documentation/SubmitChecklist when testing your code ***
> > > > > 
> > > > > The -mm tree is included into linux-next and is updated
> > > > > there every 3-4 working days
> > > > > 
> > > > > ------------------------------------------------------
> > > > > From: Shaohua Li <shli@fb.com>
> > > > > Subject: mm: reclaim MADV_FREE pages
> > > > > 
> > > > > When memory pressure is high, we free MADV_FREE pages.  If the pages are
> > > > > not dirty in pte, the pages could be freed immediately.  Otherwise we
> > > > > can't reclaim them.  We put the pages back to anonumous LRU list (by
> > > > > setting SwapBacked flag) and the pages will be reclaimed in normal swapout
> > > > > way.
> > > > > 
> > > > > We use normal page reclaim policy.  Since MADV_FREE pages are put into
> > > > > inactive file list, such pages and inactive file pages are reclaimed
> > > > > according to their age.  This is expected, because we don't want to
> > > > > reclaim too many MADV_FREE pages before used once pages.
> > > > > 
> > > > > Based on Minchan's original patch
> > > > > 
> > > > > Link: http://lkml.kernel.org/r/14b8eb1d3f6bf6cc492833f183ac8c304e560484.1487965799.git.shli@fb.com
> > > > > Signed-off-by: Shaohua Li <shli@fb.com>
> > > > > Acked-by: Minchan Kim <minchan@kernel.org>
> > > > > Acked-by: Michal Hocko <mhocko@suse.com>
> > > > > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > > > > Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
> > > > > Cc: Hugh Dickins <hughd@google.com>
> > > > > Cc: Rik van Riel <riel@redhat.com>
> > > > > Cc: Mel Gorman <mgorman@techsingularity.net>
> > > > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > > > > ---
> > > > 
> > > > < snip >
> > > > 
> > > > > @@ -1419,11 +1413,21 @@ static int try_to_unmap_one(struct page
> > > > >  			VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
> > > > >  				page);
> > > > >  
> > > > > -			if (!PageDirty(page)) {
> > > > > +			/*
> > > > > +			 * swapin page could be clean, it has data stored in
> > > > > +			 * swap. We can't silently discard it without setting
> > > > > +			 * swap entry in the page table.
> > > > > +			 */
> > > > > +			if (!PageDirty(page) && !PageSwapCache(page)) {
> > > > >  				/* It's a freeable page by MADV_FREE */
> > > > >  				dec_mm_counter(mm, MM_ANONPAGES);
> > > > > -				rp->lazyfreed++;
> > > > >  				goto discard;
> > > > > +			} else if (!PageSwapBacked(page)) {
> > > > > +				/* dirty MADV_FREE page */
> > > > > +				set_pte_at(mm, address, pvmw.pte, pteval);
> > > > > +				ret = SWAP_DIRTY;
> > > > > +				page_vma_mapped_walk_done(&pvmw);
> > > > > +				break;
> > > > >  			}
> > > > 
> > > > There is no point to make this logic complicated with clean swapin-page.
> > > > 
> > > > Andrew,
> > > > Could you fold below patch into the mm-reclaim-madv_free-pages.patch
> > > > if others are not against?
> > > > 
> > > > Thanks.
> > > > 
> > > > From 0c28f6560fbc4e65da4f4a8cc4664ab9f7b11cf3 Mon Sep 17 00:00:00 2001
> > > > From: Minchan Kim <minchan@kernel.org>
> > > > Date: Fri, 3 Mar 2017 11:42:52 +0900
> > > > Subject: [PATCH] mm: clean up lazyfree page handling
> > > > 
> > > > We can make it simple to understand without need to be aware of
> > > > clean-swapin page.
> > > > This patch just clean up lazyfree page handling in try_to_unmap_one.
> > > > 
> > > > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > > 
> > > Agreed, this is a litle easier to follow.
> > > 
> > > Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> > 
> > Thanks, Johannes.
> > 
> > > 
> > > > ---
> > > >  mm/rmap.c | 22 +++++++++++-----------
> > > >  1 file changed, 11 insertions(+), 11 deletions(-)
> > > > 
> > > > diff --git a/mm/rmap.c b/mm/rmap.c
> > > > index bb45712..f7eab40 100644
> > > > --- a/mm/rmap.c
> > > > +++ b/mm/rmap.c
> > > > @@ -1413,17 +1413,17 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> > > >  			VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
> > > >  				page);
> > > 
> > > Since you're removing the PageSwapCache() check and we're now assuming
> > > that !swapbacked is not in the swapcache, can you modify this to check
> > > PageSwapBacked(page) != PageSwapCache(page)?
> > > 
> > > Better yet, change it into a warning and SWAP_FAIL.
> > 
> > Maybe, what you wanted is
> > 
> >  !!PageSwapBacked(page) != !!PageSwapCache(page)
> 
> Those testers return 0 or 1 ints, on x86 even bool.

You're right.
It seems PageXXX() was not in old day. Hmm, but seem to have corrected.

> 
> > Personally, I prefer && style rather than equation expression
> > in this case.
> 
> > @@ -1413,20 +1413,24 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> >  			 * Store the swap location in the pte.
> >  			 * See handle_pte_fault() ...
> >  			 */
> > -			VM_BUG_ON_PAGE(!PageSwapCache(page) && PageSwapBacked(page),
> > -				page);
> > +			if (VM_WARN_ON_ONCE(PageSwapBacked(page) &&
> > +						!PageSwapCache(page))) {
> > +				ret = SWAP_FAIL;
> 
> But you're not adding the !swapbacked && swapcache case?

PageSwapcache checks already includes PageSwapBacked check so practically,
it would be pointless at this moment. But yes, it would be bad on relying
on the current implemenation as considering the future.

As a bonus from side-effect, seeing the warning always only means
it is from PageSwapbacked && !swapcache so we don't need to introduce
VM_WARN_ON_ONCE_PAGE at this moment. :)

I will resend it.

Thanks for the review!