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    SubjectRe: [PATCH v3 16/21] mm: handle lruvec relocks in compaction
    On Thu, 23 Feb 2012 17:52:56 +0400
    Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

    > Prepare for lru_lock splitting in memory compaction code.
    >
    > * disable irqs in acct_isolated() for __mod_zone_page_state(),
    > lru_lock isn't required there.
    >
    > Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
    > ---
    > mm/compaction.c | 30 ++++++++++++++++--------------
    > 1 files changed, 16 insertions(+), 14 deletions(-)
    >
    > diff --git a/mm/compaction.c b/mm/compaction.c
    > index a976b28..54340e4 100644
    > --- a/mm/compaction.c
    > +++ b/mm/compaction.c
    > @@ -224,8 +224,10 @@ static void acct_isolated(struct zone *zone, struct compact_control *cc)
    > list_for_each_entry(page, &cc->migratepages, lru)
    > count[!!page_is_file_cache(page)]++;
    >
    > + local_irq_disable();
    > __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
    > __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
    > + local_irq_enable();

    Why we need to disable Irq here ??



    > }
    >
    > /* Similar to reclaim, but different enough that they don't share logic */
    > @@ -262,7 +264,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    > unsigned long nr_scanned = 0, nr_isolated = 0;
    > struct list_head *migratelist = &cc->migratepages;
    > isolate_mode_t mode = ISOLATE_ACTIVE|ISOLATE_INACTIVE;
    > - struct lruvec *lruvec;
    > + struct lruvec *lruvec = NULL;
    >
    > /* Do not scan outside zone boundaries */
    > low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
    > @@ -294,25 +296,24 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    >
    > /* Time to isolate some pages for migration */
    > cond_resched();
    > - spin_lock_irq(&zone->lru_lock);
    > for (; low_pfn < end_pfn; low_pfn++) {
    > struct page *page;
    > - bool locked = true;
    >
    > /* give a chance to irqs before checking need_resched() */
    > if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
    > - spin_unlock_irq(&zone->lru_lock);
    > - locked = false;
    > + if (lruvec)
    > + unlock_lruvec_irq(lruvec);
    > + lruvec = NULL;
    > }
    > - if (need_resched() || spin_is_contended(&zone->lru_lock)) {
    > - if (locked)
    > - spin_unlock_irq(&zone->lru_lock);
    > + if (need_resched() ||
    > + (lruvec && spin_is_contended(&zone->lru_lock))) {
    > + if (lruvec)
    > + unlock_lruvec_irq(lruvec);
    > + lruvec = NULL;
    > cond_resched();
    > - spin_lock_irq(&zone->lru_lock);
    > if (fatal_signal_pending(current))
    > break;
    > - } else if (!locked)
    > - spin_lock_irq(&zone->lru_lock);
    > + }
    >
    > /*
    > * migrate_pfn does not necessarily start aligned to a
    > @@ -359,7 +360,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    > continue;
    > }
    >
    > - if (!PageLRU(page))
    > + if (!__lock_page_lruvec_irq(&lruvec, page))
    > continue;

    Could you add more comments onto __lock_page_lruvec_irq() ?

    Thanks,
    -Kame



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