On Thu, Sep 06, 2012 at 01:24:49PM +0100, Mel Gorman wrote: > On Thu, Sep 06, 2012 at 06:44:29PM +0800, Shaohua Li 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. > > > > Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx> > > --- > > mm/compaction.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > Index: linux/mm/compaction.c > > =================================================================== > > --- linux.orig/mm/compaction.c 2012-09-06 14:46:13.923144263 +0800 > > +++ linux/mm/compaction.c 2012-09-06 14:46:58.118588574 +0800 > > @@ -295,9 +295,9 @@ isolate_migratepages_range(struct zone * > > } > > > > /* Time to isolate some pages for migration */ > > - cond_resched(); > > Why did you remove the cond_resched()? I expect it's because > compact_checklock_irqsave() does a need_resched() check and if it is true > will either call cond_resched() or abort compaction. If it is aborting it > will not call cond_resched() but there is a reasonable expectation that > the caller will schedule soon. If this is the reasoning then it should be > included in the changelog. If it's an accident then leave the cond_resched() > where it is. Ok, looks I overlooked at it, will change it in next post. > > - spin_lock_irqsave(&zone->lru_lock, flags); > > - locked = true; > > + locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc); > > + if (!locked) > > + goto skip; > > There is no need for the goto. No useful work has taken place at this > point and there is no need to even trigger the tracepoint. Just return > 0. Just want to print out something in trace, but that's fine, I'll fix this. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>