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

[Johannes Weiner]

On Fri, Mar 03, 2017 at 11:52:37AM +0900, Minchan Kim wrote:
> On Tue, Feb 28, 2017 at 04:32:38PM -0800, akpm@xxxxxxxxxxxxxxxxxxxx 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@xxxxxx>
> > 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@xxxxxx
> > Signed-off-by: Shaohua Li <shli@xxxxxx>
> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Rik van Riel <riel@xxxxxxxxxx>
> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > ---
> 
> < 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@xxxxxxxxxx>
> 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@xxxxxxxxxx>

Agreed, this is a litle easier to follow.

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

> ---
>  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.