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SubjectRe: [PATCH 1/5] Swap Migration V5: LRU operations
Christoph Lameter <clameter@engr.sgi.com> 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.

But lru_add_drain_per_cpu() will be called from interrupt context: the IPI
handler.

I'm asking whether it is safe for the IPI handler to reenable interupts on
all architectures. It might be so, but I don't recall ever having seen it
discussed, nor have I seen code which does it.
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