On Mon, 4 Dec 2006 14:07:47 +0000
[email protected] (Mel Gorman) wrote:
> o copy_strings() and variants are no longer setting the flag as the pages
> are not obviously movable when I took a much closer look.
>
> o The arch function alloc_zeroed_user_highpage() is now called
> __alloc_zeroed_user_highpage and takes flags related to
> movability that will be applied. alloc_zeroed_user_highpage()
> calls __alloc_zeroed_user_highpage() with no additional flags to
> preserve existing behavior of the API for out-of-tree users and
> alloc_zeroed_user_highpage_movable() sets the __GFP_MOVABLE flag.
>
> o new_inode() documents that it uses GFP_HIGH_MOVABLE and callers are expected
> to call mapping_set_gfp_mask() if that is not suitable.
umm, OK. Could we please have some sort of statement pinning down the
exact semantics of __GFP_MOVABLE, and what its envisaged applications are?
My concern is that __GFP_MOVABLE is useful for fragmentation-avoidance, but
useless for memory hot-unplug. So that if/when hot-unplug comes along
we'll add more gunk which is a somewhat-superset of the GFP_MOVABLE
infrastructure, hence we didn't need the GFP_MOVABLE code. Or something.
That depends on how we do hot-unplug, if we do it. I continue to suspect
that it'll be done via memory zones: effectively by resurrecting
GFP_HIGHMEM. In which case there's little overlap with anti-frag. (btw, I
have a suspicion that the most important application of memory hot-unplug
will be power management: destructively turning off DIMMs).
I'd also like to pin down the situation with lumpy-reclaim versus
anti-fragmentation. No offence, but I would of course prefer to avoid
merging the anti-frag patches simply based on their stupendous size. It
seems to me that lumpy-reclaim is suitable for the e1000 problem, but
perhaps not for the hugetlbpage problem. Whereas anti-fragmentation adds
vastly more code, but can address both problems? Or something.
IOW: big-picture where-do-we-go-from-here stuff.
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