Re: [PATCH V7 2/2] mm: memcg detect no memcgs above softlimit under zone reclaim

[Rik van Riel <riel@redhat.com>]

On 08/01/2012 03:04 PM, Ying Han wrote:

> That is true. Hmm, then two things i can do:
>
> 1. for kswapd case, make sure not counting the root cgroup
> 2. or check nr_scanned. I like the nr_scanned which is telling us
> whether or not the reclaim ever make any attempt ?

I am looking at a more advanced case of (3) right
now.  Once I have the basics working, I will send
you a prototype (that applies on top of your patches)
to play with.

Basically, for every LRU in the system, we can keep
track of 4 things:
- reclaim_stat->recent_scanned
- reclaim_stat->recent_rotated
- reclaim_stat->recent_pressure
- LRU size

The first two represent the fraction of pages on the
list that are actively used.  The larger the fraction
of recently used pages, the more valuable the cache
is. The inverse of that can be used to show us how
hard to reclaim this cache, compared to other caches
(everything else being equal).

The recent pressure can be used to keep track of how
many pages we have scanned on each LRU list recently.
Pressure is scaled with LRU size.

This would be the basic formula to decide which LRU
to reclaim from:

           recent_scanned   LRU size
score =   -------------- * ----------------
           recent_rotated   recent_pressure


In other words, the less the objects on an LRU are
used, the more we should reclaim from that LRU. The
larger an LRU is, the more we should reclaim from
that LRU.

The more we have already scanned an LRU, the lower
its score becomes. At some point, another LRU will
have the top score, and that will be the target to
scan.

We can adjust the score for different LRUs in different
ways, eg.:
- swappiness adjustment for file vs anon LRUs, within
   an LRU set
- if an LRU set contains a file LRU with more inactive
   than active pages, reclaim from this LRU set first
- if an LRU set is over it's soft limit, reclaim from
   this LRU set first

This also gives us a nice way to balance memory pressure
between zones, etc...

--
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>