Re: [PATCH/RFC 3/14] Reclaim Scalability: move isolate_lru_page() to vmscan.c

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

On Mon, 2007-09-17 at 14:50 +0530, Balbir Singh wrote:
> Lee Schermerhorn wrote:
> > +int isolate_lru_page(struct page *page)
> > +{
> > +	int ret = -EBUSY;
> > +
> > +	if (PageLRU(page)) {
> > +		struct zone *zone = page_zone(page);
> > +
> > +		spin_lock_irq(&zone->lru_lock);
> > +		if (PageLRU(page)) {
> > +			ret = 0;
> > +			ClearPageLRU(page);
> > +			if (PageActive(page))
> > +				del_page_from_active_list(zone, page);
> > +			else
> > +				del_page_from_inactive_list(zone, page);
> > +		}
> 
> Wouldn't using a pagelist as an argument and moving to that be easier?
> Are there any cases where we just remove from the list and not move it
> elsewhere?

Actually, isolate_lru_page() used to do that, and Nick removed that
aspect for use with the mlock patches--so as not to have to use a dummy
list for single pages in the mlock code.  Nick's way is probably OK
performance-wise for the current usage in migration and mlock code.
Might need to rethink this if this function gets wider usage, now that
it's globally visible.

> 
> > +		spin_unlock_irq(&zone->lru_lock);
> > +	}
> > +	return ret;
> > +}
> > +
> 
> Any chance we could merge __isolate_lru_page() and isolate_lru_page()?

I wondered about this in one of the patch descriptions.  Peter Z
proposed a wrapper around __isolate_lru_pages() to do this.  The other
changes that I made to __isolate_lru_pages complicate this a bit, but I
think it could be managable.  Note that isolate_lru_page() is called
with the zone lru_lock unlocked and it updates the list stats.
__isolate_lru_page is called from a batch *isolate_lru_pages*() function
and does not update the stats.  The wrapper can handle these extra
tasks, I think--efficiently, I hope.

Lee

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