Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs aredisabled while isolating pages for migration

From: Andrea Arcangeli
Date: Mon Feb 28 2011 - 18:07:48 EST

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

> 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?

> 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.
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