Re: [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock

[Matthew Wilcox]

On Tue, Nov 19, 2019 at 08:23:17PM +0800, Alex Shi wrote:
> +static inline struct lruvec *lock_page_lruvec_irqsave(struct page *page,
> +				struct pglist_data *pgdat, unsigned long *flags)
> +{
> +	struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);
> +
> +	spin_lock_irqsave(&lruvec->lru_lock, *flags);
> +
> +	return lruvec;
> +}

This should be a macro, not a function.  You basically can't do this;
spin_lock_irqsave needs to write to a variable which can then be passed
to spin_unlock_irqrestore().  What you're doing here will dereference the
pointer in _this_ function, but won't propagate the modified value back to
the caller.  I suppose you could do something like this ...

static inline struct lruvec *lock_page_lruvec_irqsave(struct page *page,
			struct pglist_data *pgdat, unsigned long *flagsp)
{
	unsigned long flags;
	struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);

	spin_lock_irqsave(&lruvec->lru_lock, flags);
	*flagsp = flags;

	return lruvec;
}

Almost certainly easier to write a macro though.

You shouldn't need the two prior patches with this kind of change.