On Fri, Nov 11, 2016 at 02:30:39AM -0800, David Rientjes wrote:

On Fri, 11 Nov 2016, Joonsoo Kim wrote:

quoted

Hello, David.

Maintaining acitve/free_slab counters looks so complex. And, I think
that we don't need to maintain these counters for faster slabinfo.
Key point is to remove iterating n->slabs_partial list.

We can calculate active slab/object by following equation as you did in
this patch.

active_slab(n) = n->num_slab - the number of free_slab
active_object(n) = n->num_slab * cachep->num - n->free_objects

To get the number of free_slab, we need to iterate n->slabs_free list
but I guess it would be small enough.

If you don't like to iterate n->slabs_free list in slabinfo, just
maintaining the number of slabs_free would be enough.

Hi Joonsoo,

It's a good point, although I don't think the patch has overly complex 
logic to keep track of slab state.

We don't prefer to do any iteration in get_slabinfo() since users can 
read /proc/slabinfo constantly; it's better to just settle the stats when 
slab state changes instead of repeating an expensive operation over and 
over if someone is running slabtop(1) or /proc/slabinfo is scraped 
regularly for stats.

That said, I imagine there are more clever ways to arrive at the same 
answer, and you bring up a good point about maintaining a n->num_slabs and 
n->free_slabs rather than n->active_slabs and n->free_slabs.

I don't feel strongly about either approach, but I think some improvement, 
such as what this patch provides, is needed to prevent how expensive 
simply reading /proc/slabinfo can be.

Hello,

Sorry for long delay.
I agree that this improvement is needed. Could you try the approach
that maintains n->num_slabs and n->free_slabs? I guess that it would be
simpler than this patch so more maintainable.

Thanks.

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