Re: [PATCH 1/5] Swap Migration V5: LRU operations

[Lee Schermerhorn <lee.schermerhorn@hp.com>]

On Tue, 2005-11-15 at 08:38 -0800, Christoph Lameter wrote:
> On Mon, 14 Nov 2005, Andrew Morton wrote:
> 
> > >  +int isolate_lru_page(struct page *page)
> > >  +{
> > >  +	int rc = 0;
> > >  +	struct zone *zone = page_zone(page);
> > >  +
> > >  +redo:
> > >  +	spin_lock_irq(&zone->lru_lock);
> > >  +	rc = __isolate_lru_page(zone, page);
> > >  +	spin_unlock_irq(&zone->lru_lock);
> > >  +	if (rc == 0) {
> > >  +		/*
> > >  +		 * Maybe this page is still waiting for a cpu to drain it
> > >  +		 * from one of the lru lists?
> > >  +		 */
> > >  +		smp_call_function(&lru_add_drain_per_cpu, NULL, 0 , 1);
> > 
> > lru_add_drain() ends up doing spin_unlock_irq(), so we'll enable interrupts
> > within the smp_call_function() handler.  Is that legal on all
> > architectures?
> 
> isolate_lru_pages() is only called within a process context in the swap 
> migration patches. The hotplug folks may have to address this if they want 
> to isolate pages from interrupts etc.
> 

I believe Andrew is refering to the calls from the interprocessor
interrupt handlers triggered by the smp_call_function().  Looks like
ia64 runs IPI handlers with interrupts enabled [SA_INTERRUPT], so should
be OK there, but maybe not for all archs?

Lee