On Mon, 10 Sep 2012 09:18:50 +0800
Shaohua Li <shli@xxxxxxxxxx> wrote:
> isolate_migratepages_range will take zone->lru_lock first and check if the lock
> is contented, if yes, it will release the lock. This isn't efficient. If the
> lock is truly contented, a lock/unlock pair will increase the lock contention.
> We'd better check if the lock is contended first. compact_trylock_irqsave
> perfectly meets the requirement.
>
> V2:
> leave cond_resched() pointed out by Mel.
>
> Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
> ---
> mm/compaction.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> Index: linux/mm/compaction.c
> ===================================================================
> --- linux.orig/mm/compaction.c 2012-09-10 08:49:40.377869710 +0800
> +++ linux/mm/compaction.c 2012-09-10 08:53:10.295230575 +0800
> @@ -295,8 +295,9 @@ isolate_migratepages_range(struct zone *
>
> /* Time to isolate some pages for migration */
> cond_resched();
> - spin_lock_irqsave(&zone->lru_lock, flags);
> - locked = true;
> + locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc);
> + if (!locked)
> + return 0;
> for (; low_pfn < end_pfn; low_pfn++) {
> struct page *page;
Geeze that compact_checklock_irqsave stuff is naaaasty.
What happens if a process has need_resched set? It cannot perform
compaction? There is no relationship between the concepts "user
pressed ^C" and "this device driver or subsystem wants a high-order
allocation".
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