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    SubjectRe: [PATCH 06/10] vmscan: Split shrink_zone to reduce stack usage
    On Thu, Apr 15, 2010 at 06:21:39PM +0100, Mel Gorman wrote:
    > shrink_zone() calculculates how many pages it needs to shrink from each
    > LRU list in a given pass. It uses a number of temporary variables to
    > work this out that then remain on the stack. This patch splits the
    > function so that some of the stack variables can be discarded.
    >
    > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > ---
    > mm/vmscan.c | 29 +++++++++++++++++++----------
    > 1 files changed, 19 insertions(+), 10 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 1ace7c6..a374879 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -1595,19 +1595,14 @@ static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
    > return nr;
    > }
    >
    > -/*
    > - * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
    > - */
    > -static void shrink_zone(struct zone *zone, struct scan_control *sc)
    > +/* Calculate how many pages from each LRU list should be scanned */
    > +static void calc_scan_trybatch(struct zone *zone,
    > + struct scan_control *sc, unsigned long *nr)
    > {
    > - unsigned long nr[NR_LRU_LISTS];
    > - unsigned long nr_to_scan;
    > - unsigned long percent[2]; /* anon @ 0; file @ 1 */
    > enum lru_list l;
    > - unsigned long nr_reclaimed = sc->nr_reclaimed;
    > - unsigned long nr_to_reclaim = sc->nr_to_reclaim;
    > + unsigned long percent[2]; /* anon @ 0; file @ 1 */
    > + int noswap = 0 ;
    > struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
    > - int noswap = 0;
    >
    > /* If we have no swap space, do not bother scanning anon pages. */
    > if (!sc->may_swap || (nr_swap_pages <= 0)) {
    > @@ -1629,6 +1624,20 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
    > nr[l] = nr_scan_try_batch(scan,
    > &reclaim_stat->nr_saved_scan[l]);
    > }
    > +}
    > +
    > +/*
    > + * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
    > + */
    > +static void shrink_zone(struct zone *zone, struct scan_control *sc)
    > +{
    > + unsigned long nr[NR_LRU_LISTS];
    > + unsigned long nr_to_scan;
    > + unsigned long nr_reclaimed = sc->nr_reclaimed;
    > + unsigned long nr_to_reclaim = sc->nr_to_reclaim;
    > + enum lru_list l;
    > +
    > + calc_scan_trybatch(zone, sc, nr);

    Uh, that does not sound very nice! How about calculate_scan_work() or
    something like that? Might as well use the function to abstract detail :)

    Other than that (and with the noinline_for_stack):

    Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>


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