Messages in this thread | | | Subject | Re: [patch] zone_watermark_ok() rework | From | Nick Piggin <> | Date | Tue, 04 Oct 2005 10:38:14 +1000 |
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On Tue, 2005-10-04 at 01:41 +0800, Coywolf Qi Hunt wrote: > Hello, > > In zone_watermark_ok(), the original algorithm seems not logical. This is a > rework. Comments? > > Coywolf > > > Signed-off-by: Coywolf Qi Hunt <coywolf@sosdg.org> > --- > > page_alloc.c | 15 +++++---------- > 1 file changed, 5 insertions(+), 10 deletions(-) > > --- 2.6.14-rc2-mm1/mm/page_alloc.c~orig 2005-09-29 20:37:07.000000000 +0800 > +++ 2.6.14-rc2-mm1/mm/page_alloc.c 2005-10-04 01:19:31.000000000 +0800 > @@ -772,7 +772,7 @@ > int zone_watermark_ok(struct zone *z, int order, unsigned long mark, > int classzone_idx, int can_try_harder, int gfp_high) > { > - /* free_pages my go negative - that's OK */ > + /* free_pages may go negative - that's OK */ > long min = mark, free_pages = z->free_pages - (1 << order) + 1; > int o; >
Typo. Thanks.
> @@ -783,17 +783,12 @@ > > if (free_pages <= min + z->lowmem_reserve[classzone_idx]) > return 0; > - for (o = 0; o < order; o++) { > - /* At the next order, this order's pages become unavailable */ > - free_pages -= z->free_area[o].nr_free << o; > > - /* Require fewer higher order pages to be free */ > - min >>= 1; > - > - if (free_pages <= min) > - return 0; > + for (o = order; o < MAX_ORDER; o++) { > + if (z->free_area[o].nr_free) > + return 1; > } > - return 1; > + return 0; > } > > static inline int
Well the original algorithm's intention is to include some watermarks for higher order pages for eg. GFP_ATOMIC and PF_MEMALLOC. To that goal I believe the algorithm is logical?
Yours is correct if our intention was simply to ensure _any_ higher order page is available, however it is also redundant because rmqueue will catch that for us. However, that is not the intention :)
Any reasons why it should be changed?
Thanks, Nick
-- SUSE Labs, Novell Inc.
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