Re: computing drop-able caches
From: Johannes Weiner <hannes@cmpxchg.org>
Date: 2016-01-29 22:33:46
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On Fri, Jan 29, 2016 at 01:21:47PM -0800, Daniel Walker wrote:
On 01/28/2016 05:55 PM, Johannes Weiner wrote:quoted
On Thu, Jan 28, 2016 at 05:29:41PM -0800, Daniel Walker wrote:quoted
On 01/28/2016 05:03 PM, Daniel Walker wrote: [regarding MemAvaiable] This new metric purportedly helps usrespace assess available memory. But, its again based on heuristic, it takes 1/2 of page cache as reclaimable..No, it takes the smaller value of cache/2 and the low watermark, which is a fraction of memory. Actually, that does look a little weird. Rik? We don't age cache without memory pressure, you don't know how much is used until you start taking some away. Heuristics is all we can offer.With a simple busybox root system I get this, MemTotal: 16273996 kB MemFree: 16137920 kB MemAvailable: 16046132 kB shouldn't MemAvailable be at least the same as MemFree ? I changed the code somewhat so it subtracted the wmark_low only, or the pagecache/2 only, both are still under MemFree. This system has very little drop-able caches.
No, a portion of memory is reserved for the kernel and not available to userland. If the kernel doesn't use it it will remain free. Hence the lower MemAvailable. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>