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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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