On Fri, Jan 29, 2016 at 01:21:47PM -0800, Daniel Walker wrote: > On 01/28/2016 05:55 PM, Johannes Weiner wrote: > >On Thu, Jan 28, 2016 at 05:29:41PM -0800, Daniel Walker wrote: > >>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.
