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    SubjectRe: [PATCH 16/22] Do not setup zonelist cache when there is only one node
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    On Wed, 2009-04-22 at 13:24 -0700, David Rientjes wrote:
    > On Wed, 22 Apr 2009, Mel Gorman wrote:
    >
    > > There is a zonelist cache which is used to track zones that are not in
    > > the allowed cpuset or found to be recently full. This is to reduce cache
    > > footprint on large machines. On smaller machines, it just incurs cost
    > > for no gain. This patch only uses the zonelist cache when there are NUMA
    > > nodes.
    > >
    > > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > > Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
    > > ---
    > > mm/page_alloc.c | 7 +++++--
    > > 1 files changed, 5 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > > index 7f45de1..e59bb80 100644
    > > --- a/mm/page_alloc.c
    > > +++ b/mm/page_alloc.c
    > > @@ -1467,8 +1467,11 @@ this_zone_full:
    > > if (NUMA_BUILD)
    > > zlc_mark_zone_full(zonelist, z);
    >
    > If zonelist caching is never used for UMA machines, why should they ever
    > call zlc_mark_zone_full()? It will always dereference
    > zonelist->zlcache_ptr and immediately return without doing anything.
    >
    > Wouldn't it better to just add
    >
    > if (num_online_nodes() == 1)
    > continue;
    >
    > right before this call to zlc_mark_zone_full()? This should compile out
    > the remainder of the loop for !CONFIG_NUMA kernels anyway.

    Shouldn't it already do that? NUMA_BUILD is defined as 0 when
    !CONFIG_NUMA to avoid #ifdef's in the code while still allowing compiler
    error checking in the dead code.

    Lee

    >
    > > try_next_zone:
    > > - if (NUMA_BUILD && !did_zlc_setup) {
    > > - /* we do zlc_setup after the first zone is tried */
    > > + if (NUMA_BUILD && !did_zlc_setup && num_online_nodes() > 1) {
    > > + /*
    > > + * we do zlc_setup after the first zone is tried but only
    > > + * if there are multiple nodes make it worthwhile
    > > + */
    > > allowednodes = zlc_setup(zonelist, alloc_flags);
    > > zlc_active = 1;
    > > did_zlc_setup = 1;
    > > --
    > > 1.5.6.5
    >
    > --
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