Re: [PATCH 2/6] mm: differentiate unmap for vmscan from other unmap.

[Jerome Glisse]

On Sun, Jun 29, 2014 at 08:58:17PM -0700, John Hubbard wrote:
> On Fri, 27 Jun 2014, Jérôme Glisse wrote:
> 
> > From: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > 
> > New code will need to be able to differentiate between a regular unmap and
> > an unmap trigger by vmscan in which case we want to be as quick as possible.
> > 
> > Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > ---
> >  include/linux/rmap.h | 15 ++++++++-------
> >  mm/memory-failure.c  |  2 +-
> >  mm/vmscan.c          |  4 ++--
> >  3 files changed, 11 insertions(+), 10 deletions(-)
> > 
> > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> > index be57450..eddbc07 100644
> > --- a/include/linux/rmap.h
> > +++ b/include/linux/rmap.h
> > @@ -72,13 +72,14 @@ struct anon_vma_chain {
> >  };
> >  
> >  enum ttu_flags {
> > -	TTU_UNMAP = 1,			/* unmap mode */
> > -	TTU_MIGRATION = 2,		/* migration mode */
> > -	TTU_MUNLOCK = 4,		/* munlock mode */
> > -
> > -	TTU_IGNORE_MLOCK = (1 << 8),	/* ignore mlock */
> > -	TTU_IGNORE_ACCESS = (1 << 9),	/* don't age */
> > -	TTU_IGNORE_HWPOISON = (1 << 10),/* corrupted page is recoverable */
> > +	TTU_VMSCAN = 1,			/* unmap for vmscan */
> > +	TTU_POISON = 2,			/* unmap for poison */
> > +	TTU_MIGRATION = 4,		/* migration mode */
> > +	TTU_MUNLOCK = 8,		/* munlock mode */
> > +
> > +	TTU_IGNORE_MLOCK = (1 << 9),	/* ignore mlock */
> > +	TTU_IGNORE_ACCESS = (1 << 10),	/* don't age */
> > +	TTU_IGNORE_HWPOISON = (1 << 11),/* corrupted page is recoverable */
> 
> Unless there is a deeper purpose that I am overlooking, I think it would 
> be better to leave the _MLOCK, _ACCESS, and _HWPOISON at their original 
> values. I just can't quite see why they would need to start at bit 9 
> instead of bit 8...

This code change to have various TTU_* be bitflag instead of value. I am
not sure what was the win in that, would need to dig up that patch that
did that. But in all the case i preserve that change here hence starting
at 9.
> 
> >  };
> >  
> >  #ifdef CONFIG_MMU
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index a7a89eb..ba176c4 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -887,7 +887,7 @@ static int page_action(struct page_state *ps, struct page *p,
> >  static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
> >  				  int trapno, int flags, struct page **hpagep)
> >  {
> > -	enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
> > +	enum ttu_flags ttu = TTU_POISON | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
> >  	struct address_space *mapping;
> >  	LIST_HEAD(tokill);
> >  	int ret;
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 6d24fd6..5a7d286 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1163,7 +1163,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
> >  	}
> >  
> >  	ret = shrink_page_list(&clean_pages, zone, &sc,
> > -			TTU_UNMAP|TTU_IGNORE_ACCESS,
> > +			TTU_VMSCAN|TTU_IGNORE_ACCESS,
> >  			&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
> >  	list_splice(&clean_pages, page_list);
> >  	mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
> > @@ -1518,7 +1518,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> >  	if (nr_taken == 0)
> >  		return 0;
> >  
> > -	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
> > +	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_VMSCAN,
> >  				&nr_dirty, &nr_unqueued_dirty, &nr_congested,
> >  				&nr_writeback, &nr_immediate,
> >  				false);
> > -- 
> > 1.9.0
> > 
> > --
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> > the body to majordomo@xxxxxxxxxx  For more info on Linux MM,
> > see: http://www.linux-mm.org/ .
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> > 
> 
> Other than that, looks good.
> 
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> 
> thanks,
> John H.

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