On Wed, Feb 08, 2017 at 02:23:19PM +0100, Thomas Gleixner wrote: > On Wed, 8 Feb 2017, Mel Gorman wrote: > > It may be worth noting that patches in Andrew's tree no longer disable > > interrupts in the per-cpu allocator and now per-cpu draining will > > be from workqueue context. The reasoning was due to the overhead of > > the page allocator with figures included. Interrupts will bypass the > > per-cpu allocator and use the irq-safe zone->lock to allocate from > > the core. It'll collide with the RT patch. Primary patch of interest is > > http://www.ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch > > Yeah, we'll sort that out once it hits Linus tree and we move RT forward. > Though I have once complaint right away: > > + preempt_enable_no_resched(); > > This is a nono, even in mainline. You effectively disable a preemption > point. > This came up during review on whether it should or shouldn't be a preemption point. Initially it was preempt_enable() but a preemption point didn't exist before, the reviewer pushed for it and as it was the allocator fast path that was unlikely to need a reschedule or preempt, I made the change. I can alter it before it hits mainline if you say RT is going to have an issue with it. > > The draining from workqueue context may be a problem for RT but one > > option would be to move the drain to only drain for high-order pages > > after direct reclaim combined with only draining for order-0 if > > __alloc_pages_may_oom is about to be called. > > Why would the draining from workqueue context be an issue on RT? > It probably isn't. The latency of the operation is likely longer than an IPI was but given the context it occurs in, I severely doubted it mattered. I couldn't think of a reason why it would matter to RT but there was no harm double checking. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
