Messages in this thread | | | Date | Mon, 23 Jul 2018 16:04:20 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 13/19] mm/migrate: Use xchg instead of spinlock |
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On Mon, Jul 23, 2018 at 04:20:32AM -0700, Srikar Dronamraju wrote: > > If you maybe write that like: > > > > if (time_after(jiffies, next_window) && > > xchg(&pgdat->numabalancing_migrate_nr_pages, 0UL)) { > > > > do { > > next_window += interval; > > } while (unlikely(time_after(jiffies, next_window))); > > > > WRITE_ONCE(pgdat->numabalancing_migrate_next_window, next_window); > > } > > > > Then you avoid an indent level and line-wrap, resulting imo easier to > > read code. > > > > Okay will do.
FWIW, that code seems to rely on @nr_pages != 0, otherwise you can have the xchg fail even though time_after is true.
Probably not a problem, but it is a semantic change vs the spinlock. Also, the spinlock thing could probably have changed to a trylock and you'd have seens similar 'gains' I suppose.
Another difference vs the lock+unlock is that you lost the release ordering. Again, probably not a big deal, but it does make the whole things a little dodgy.
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