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    SubjectRe: [patch] zone_watermark_ok() rework
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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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