Messages in this thread | | | Date | Tue, 19 Nov 2019 11:44:48 -0500 | From | Johannes Weiner <> | Subject | Re: [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock |
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On Tue, Nov 19, 2019 at 07:57:04AM -0800, Matthew Wilcox wrote: > 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 ...
This works because spin_lock_irqsave and local_irq_save() are macros. It boils down to '*flags = arch_local_irq_save()' in this function, and therefor does the right thing.
We exploit that in quite a few places:
$ git grep 'spin_lock_irqsave(.*\*flags' | wc -l 39
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