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    SubjectRe: [RFC][PATCH] mm: remove unnecessary loop inside shrink_inactive_list()
    From
    2009/8/20 Wu Fengguang <fengguang.wu@intel.com>:
    > shrink_inactive_list() won't be called to scan too much pages
    > (unless in hibernation code which is fine) or too few pages (ie.
    > batching is taken care of by the callers).  So we can just remove the
    > big loop and isolate the exact number of pages requested.
    >
    > Just a RFC, and a scratch patch to show the basic idea.
    > Please kindly NAK quick if you don't like it ;)

    Hm, I think this patch taks only cleanups. right?
    if so, I don't find any objection reason.




    > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > ---
    >  mm/vmscan.c |   32 ++++++++++++++++----------------
    >  1 file changed, 16 insertions(+), 16 deletions(-)
    >
    > --- linux.orig/mm/vmscan.c      2009-08-20 10:16:18.000000000 +0800
    > +++ linux/mm/vmscan.c   2009-08-20 10:24:34.000000000 +0800
    > @@ -1032,16 +1032,22 @@ int isolate_lru_page(struct page *page)
    >  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
    >  * of reclaimed pages
    >  */
    > -static unsigned long shrink_inactive_list(unsigned long max_scan,
    > +static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
    >                        struct zone *zone, struct scan_control *sc,
    >                        int priority, int file)
    >  {
    >        LIST_HEAD(page_list);
    >        struct pagevec pvec;
    > -       unsigned long nr_scanned = 0;
    > -       unsigned long nr_reclaimed = 0;
    > +       unsigned long nr_reclaimed;
    >        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
    > -       int lumpy_reclaim = 0;
    > +       int lumpy_reclaim;
    > +       struct page *page;
    > +       unsigned long nr_taken;
    > +       unsigned long nr_scan;
    > +       unsigned long nr_freed;
    > +       unsigned long nr_active;
    > +       unsigned int count[NR_LRU_LISTS] = { 0, };
    > +       int mode;
    >
    >        /*
    >         * If we need a large contiguous chunk of memory, or have
    > @@ -1054,21 +1060,17 @@ static unsigned long shrink_inactive_lis
    >                lumpy_reclaim = 1;
    >        else if (sc->order && priority < DEF_PRIORITY - 2)
    >                lumpy_reclaim = 1;
    > +       else
    > +               lumpy_reclaim = 0;
    > +
    > +       mode = lumpy_reclaim ? ISOLATE_BOTH : ISOLATE_INACTIVE;
    >
    >        pagevec_init(&pvec, 1);
    >
    >        lru_add_drain();
    >        spin_lock_irq(&zone->lru_lock);
    > -       do {
    > -               struct page *page;
    > -               unsigned long nr_taken;
    > -               unsigned long nr_scan;
    > -               unsigned long nr_freed;
    > -               unsigned long nr_active;
    > -               unsigned int count[NR_LRU_LISTS] = { 0, };
    > -               int mode = lumpy_reclaim ? ISOLATE_BOTH : ISOLATE_INACTIVE;
    >
    > -               nr_taken = sc->isolate_pages(sc->swap_cluster_max,
    > +               nr_taken = sc->isolate_pages(nr_to_scan,
    >                             &page_list, &nr_scan, sc->order, mode,
    >                                zone, sc->mem_cgroup, 0, file);
    >                nr_active = clear_active_flags(&page_list, count);
    > @@ -1093,7 +1095,6 @@ static unsigned long shrink_inactive_lis
    >
    >                spin_unlock_irq(&zone->lru_lock);
    >
    > -               nr_scanned += nr_scan;
    >                nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
    >
    >                /*
    > @@ -1117,7 +1118,7 @@ static unsigned long shrink_inactive_lis
    >                                                        PAGEOUT_IO_SYNC);
    >                }
    >
    > -               nr_reclaimed += nr_freed;
    > +               nr_reclaimed = nr_freed;

    maybe, nr_freed can be removed perfectly. it have the same meaning as
    nr_reclaimed.



    >                local_irq_disable();
    >                if (current_is_kswapd()) {
    >                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
    > @@ -1158,7 +1159,6 @@ static unsigned long shrink_inactive_lis
    >                                spin_lock_irq(&zone->lru_lock);
    >                        }
    >                }
    > -       } while (nr_scanned < max_scan);
    >        spin_unlock(&zone->lru_lock);
    >  done:
    >        local_irq_enable();
    >
    > --
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