On Wed, Feb 03, 2016 at 11:06:20AM +0100, Martijn Coenen wrote: > The window size used for calculating vm pressure > events was previously fixed at 512 pages. The > window size has a big impact on the rate of notifications > sent off to userspace, in particular when using the > "low" level. On machines with a lot of memory, the > current value may be excessive. > > On the other hand, making the window size depend on > machine size does not allow userspace to change the > notification rate based on the current state of the > system. For example, when a lot of memory is still > available, userspace may want to increase the window > since it's not interested in receiving notifications > for every 2MB scanned. > > This patch makes vmpressure_window a sysctl tunable. If the machine is just cleaning up use-once cache, frequent events make no sense. And if the machine is struggling, the notifications better be in time. That's hardly a tunable. It's a factor that needs constant dynamic adjustment depending on VM state. The same state this mechanism is supposed to report. If we can't get this right, how will userspace? A better approach here would be to 1) find a minimum window size that makes us confident that there are no false positives - this is likely to be based on machine size, maybe the low watermark? - and 2) limit reporting of lower levels, so you're not flooded with ALLGOOD! events. VMPRESSURE_CRITICAL: report every vmpressure_win VMPRESSURE_MEDIUM: report every vmpressure_win*2 VMPRESSURE_LOW: report every vmpressure_win*4 Pick your favorite scaling factor here. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
