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    SubjectRe: [PATCH] mm: vmscan: handle isolated pages with lru lock released
    On Sat, 14 Jan 2012, Hillf Danton wrote:
    >
    > When shrinking inactive lru list, isolated pages are queued on locally private
    > list, so the lock-hold time could be reduced if pages are counted without lock
    > protection. To achive that, firstly updating reclaim stat is delayed until the
    > putback stage, which is pointed out by Hugh, after reacquiring the lru lock.
    >
    > Secondly operations related to vm and zone stats, are now proteced with
    > preemption disabled as they are per-cpu operation.
    >
    > Thanks for comments and ideas received.
    >
    >
    > Signed-off-by: Hillf Danton <dhillf@gmail.com>

    Thank you, I like this a lot: it undoes a little of the cleanup I just
    did, but for much better reason than I had. I'm running with it now.

    Acked-by: Hugh Dickins <hughd@google.com>

    > ---
    >
    > --- a/mm/vmscan.c Sat Jan 14 14:02:20 2012
    > +++ b/mm/vmscan.c Sat Jan 14 20:00:46 2012
    > @@ -1414,7 +1414,6 @@ update_isolated_counts(struct mem_cgroup
    > unsigned long *nr_anon,
    > unsigned long *nr_file)
    > {
    > - struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
    > struct zone *zone = mz->zone;
    > unsigned int count[NR_LRU_LISTS] = { 0, };
    > unsigned long nr_active = 0;
    > @@ -1435,6 +1434,7 @@ update_isolated_counts(struct mem_cgroup
    > count[lru] += numpages;
    > }
    >
    > + preempt_disable();
    > __count_vm_events(PGDEACTIVATE, nr_active);
    >
    > __mod_zone_page_state(zone, NR_ACTIVE_FILE,
    > @@ -1449,8 +1449,9 @@ update_isolated_counts(struct mem_cgroup
    > *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
    > *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
    >
    > - reclaim_stat->recent_scanned[0] += *nr_anon;
    > - reclaim_stat->recent_scanned[1] += *nr_file;
    > + __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
    > + __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
    > + preempt_enable();
    > }
    >
    > /*
    > @@ -1512,6 +1513,7 @@ shrink_inactive_list(unsigned long nr_to
    > unsigned long nr_writeback = 0;
    > isolate_mode_t reclaim_mode = ISOLATE_INACTIVE;
    > struct zone *zone = mz->zone;
    > + struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(mz);
    >
    > while (unlikely(too_many_isolated(zone, file, sc))) {
    > congestion_wait(BLK_RW_ASYNC, HZ/10);
    > @@ -1546,19 +1548,13 @@ shrink_inactive_list(unsigned long nr_to
    > __count_zone_vm_events(PGSCAN_DIRECT, zone,
    > nr_scanned);
    > }
    > + spin_unlock_irq(&zone->lru_lock);
    >
    > - if (nr_taken == 0) {
    > - spin_unlock_irq(&zone->lru_lock);
    > + if (nr_taken == 0)
    > return 0;
    > - }
    >
    > update_isolated_counts(mz, &page_list, &nr_anon, &nr_file);
    >
    > - __mod_zone_page_state(zone, NR_ISOLATED_ANON, nr_anon);
    > - __mod_zone_page_state(zone, NR_ISOLATED_FILE, nr_file);
    > -
    > - spin_unlock_irq(&zone->lru_lock);
    > -
    > nr_reclaimed = shrink_page_list(&page_list, mz, sc, priority,
    > &nr_dirty, &nr_writeback);
    >
    > @@ -1570,6 +1566,9 @@ shrink_inactive_list(unsigned long nr_to
    > }
    >
    > spin_lock_irq(&zone->lru_lock);
    > +
    > + reclaim_stat->recent_scanned[0] += nr_anon;
    > + reclaim_stat->recent_scanned[1] += nr_file;
    >
    > if (current_is_kswapd())
    > __count_vm_events(KSWAPD_STEAL, nr_reclaimed);


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