On Tue, 30 Nov 2010 12:44:13 -0800
Ying Han <yinghan@xxxxxxxxxx> wrote:
> On Mon, Nov 29, 2010 at 11:21 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > On Mon, 29 Nov 2010 22:49:43 -0800
> > Ying Han <yinghan@xxxxxxxxxx> wrote:
> >
> >> The per cgroup kswapd is invoked at mem_cgroup_charge when the cgroup's memory
> >> usage above a threshold--low_wmark. Then the kswapd thread starts to reclaim
> >> pages in a priority loop similar to global algorithm. The kswapd is done if the
> >> memory usage below a threshold--high_wmark.
> >>
> >> The per cgroup background reclaim is based on the per cgroup LRU and also adds
> >> per cgroup watermarks. There are two watermarks including "low_wmark" and
> >> "high_wmark", and they are calculated based on the limit_in_bytes(hard_limit)
> >> for each cgroup. Each time the hard_limit is change, the corresponding wmarks
> >> are re-calculated. Since memory controller charges only user pages, there is
> >> no need for a "min_wmark". The current calculation of wmarks is a function of
> >> "memory.min_free_kbytes" which could be adjusted by writing different values
> >> into the new api. This is added mainly for debugging purpose.
> >>
> >> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
> >
> > A few points.
> >
> > 1. I can understand the motivation for including low/high watermark to
> > Â res_coutner. But, sadly, compareing all charge will make the counter slow.
> > Â IMHO, as memory controller threshold-check or soft limit, checking usage
> > Â periodically based on event counter is enough. It will be low cost.
>
> If we have other limits using the event counter, this sounds a
> feasible try for the
> wmarks. I can look into that.
>
> >
> > 2. min_free_kbytes must be automatically calculated.
> > Â For example, max(3% of limit, 20MB) or some.
>
> Now the wmark is automatically calculated based on the limit. Adding
> the min_free_kbytes gives
> us more flexibility to adjust the portion of the threshold. This could
> just be a performance tuning
> parameter later. I need it now at least at the beginning before
> figuring out a reasonable calculation
> formula.
>
mm/page_alloc.c::init_per_zone_wmark_min() can be reused.
My question is.
> >> +void setup_per_memcg_wmarks(struct mem_cgroup *mem)
> >> +{
> >> + Â Â u64 limit;
> >> + Â Â unsigned long min_free_kbytes;
> >> +
> >> + Â Â min_free_kbytes = get_min_free_kbytes(mem);
> >> + Â Â limit = mem_cgroup_get_limit(mem);
> >> + Â Â if (min_free_kbytes == 0) {
I think this min_free_kbyte is always 0 until a user set it.
Please set this when the limit is changed, automatically.
I wonder
struct mem_cgroup {
unsigned long min_free_kbytes;
unsigned long min_free_kbytes_user_set; /* use this always if set */
}
may be necessary if we never adjust min_free_kbytes once a user set it.
Thanks,
-Kame
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