Messages in this thread | | | Date | Tue, 1 Mar 2011 08:25:08 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration |
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On Tue, Mar 01, 2011 at 12:07:12AM +0100, Andrea Arcangeli wrote: > On Tue, Mar 01, 2011 at 08:01:31AM +0900, Minchan Kim wrote: > > I am not sure it's good if we release the lock whenever lru->lock was contended > > unconditionally? There are many kinds of lru_lock operations(add to lru, > > del from lru, isolation, reclaim, activation, deactivation and so on). > > This is mostly to mirror cond_resched_lock (which actually uses > spin_needbreak but it's ok to have it also when preempt is off). I > doubt it makes a big difference but I tried to mirror > cond_resched_lock.
But what's the benefit of releasing lock in here when lock contentionn happen where activate_page for example? > > > Do we really need to release the lock whenever all such operations were contened? > > I think what we need is just spin_is_contended_irqcontext. > > Otherwise, please write down the comment for justifying for it. > > What is spin_is_contended_irqcontext?
I thought what we need function is to check lock contention happened in only irq context for short irq latency.
> > > This patch is for reducing for irq latency but do we have to check signal > > in irq hold time? > > I think it's good idea to check the signal in case the loop is very > long and this is run in direct compaction context.
I don't oppose the signal check. I am not sure why we should check by just sign of lru_lock contention.
How about this by coarse-grained?
/* give a chance to irqs before checking need_resched() */ if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) { if (fatal_signal_pending(current)) break; spin_unlock_irq(&zone->lru_lock); unlocked = true; } if (need_resched() || spin_is_contended(&zone->lru_lock)) { if (!unlocked) spin_unlock_irq(&zone->lru_lock); cond_resched(); spin_lock_irq(&zone->lru_lock); } else if (unlocked) spin_lock_irq(&zone->lru_lock);
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-- Kind regards, Minchan Kim
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