Re: [PATCH] [8/16] HWPOISON: Use bitmask/action code for try_to_unmap behaviour

Wu Fengguang
2009-06-10T02:27:44Z

On Tue, Jun 09, 2009 at 05:57:25PM +0800, Nick Piggin wrote:
> On Wed, Jun 03, 2009 at 08:46:41PM +0200, Andi Kleen wrote:
> >
> > try_to_unmap currently has multiple modi (migration, munlock, normal unmap)
> > which are selected by magic flag variables. The logic is not very straight
> > forward, because each of these flag change multiple behaviours (e.g.
> > migration turns off aging, not only sets up migration ptes etc.)
> > Also the different flags interact in magic ways.
> >
> > A later patch in this series adds another mode to try_to_unmap, so
> > this becomes quickly unmanageable.
> >
> > Replace the different flags with a action code (migration, munlock, munmap)
> > and some additional flags as modifiers (ignore mlock, ignore aging).
> > This makes the logic more straight forward and allows easier extension
> > to new behaviours. Change all the caller to declare what they want to
> > do.
> >
> > This patch is supposed to be a nop in behaviour. If anyone can prove
> > it is not that would be a bug.
> >
> > Cc: Lee.Schermerhorn@hp.com
> > Cc: npiggin@suse.de
> >
> > Signed-off-by: Andi Kleen <ak@linux.intel.com>
> >
> > ---
> > include/linux/rmap.h | 14 +++++++++++++-
> > mm/migrate.c | 2 +-
> > mm/rmap.c | 40 ++++++++++++++++++++++------------------
> > mm/vmscan.c | 2 +-
> > 4 files changed, 37 insertions(+), 21 deletions(-)
> >
> > Index: linux/include/linux/rmap.h
> > ===================================================================
> > --- linux.orig/include/linux/rmap.h 2009-06-03 19:36:23.000000000 +0200
> > +++ linux/include/linux/rmap.h 2009-06-03 20:39:50.000000000 +0200
> > @@ -84,7 +84,19 @@
> > * Called from mm/vmscan.c to handle paging out
> > */
> > int page_referenced(struct page *, int is_locked, struct mem_cgroup *cnt);
> > -int try_to_unmap(struct page *, int ignore_refs);
> > +
> > +enum ttu_flags {
> > + TTU_UNMAP = 0, /* unmap mode */
> > + TTU_MIGRATION = 1, /* migration mode */
> > + TTU_MUNLOCK = 2, /* munlock mode */
> > + TTU_ACTION_MASK = 0xff,
> > +
> > + TTU_IGNORE_MLOCK = (1 << 8), /* ignore mlock */
> > + TTU_IGNORE_ACCESS = (1 << 9), /* don't age */
> > +};
> > +#define TTU_ACTION(x) ((x) & TTU_ACTION_MASK)
>
> I still think this is nasty and should work like Gfp flags.

I don't see big problems here.

We have page_zone() and gfp_zone(), so why not TTU_ACTION()? We could
allocate one bit for each action code, but in principle they are exclusive.