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    SubjectRe: [PATCH] [8/16] HWPOISON: Use bitmask/action code for try_to_unmap behaviour
    On Wed, Jun 10, 2009 at 10:27:36AM +0800, Wu Fengguang wrote:
    > 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.

    I haven't actually applied the patchset and looked at the resulting
    try_to_unmap function, so I'll hold my tounge until I do that. I'll
    send a patch if I can find something that looks nicer. So don't worry
    about it for the moment.




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