Re: computing drop-able caches

[Daniel Walker]

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.

Daniel