Re: computing drop-able caches

From: Rik van Riel
Date: Fri Jan 29 2016 - 17:41:51 EST

On 01/28/2016 08:55 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?

No, not quite. The page cache calculation spans two lines:

pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
pagecache -= min(pagecache / 2, wmark_low);

The assumption is that ALL of active & inactive file LRUs are
freeable, except for the minimum of the low watermark, or
half the page cache.

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