[dm-devel] slab: introduce the flag SLAB_MINIMIZE_WASTE

[Mikulas Patocka]

On Mon, 16 Apr 2018, Christopher Lameter wrote:

> On Mon, 16 Apr 2018, Mikulas Patocka wrote:
> 
> > >
> > > Or an increase in slab_max_order
> >
> > But that will increase it for all slabs (often senselessly - i.e.
> > kmalloc-4096 would have order 4MB).
> 
> 4MB? Nope.... That is a power of two slab so no wasted space even with
> order 0.

See this email:
https://www.redhat.com/archives/dm-devel/2018-March/msg00387.html

If you boot with slub_max_order=10, the kmalloc-8192 cache has 64 pages. 
So yes, it increases the order of all slab caches (although not up to 
4MB).

> Its not a senseless increase. The more objects you fit into a slab page
> the higher the performance of the allocator.
> 
> 
> > I need to increase it just for dm-bufio slabs.
> 
> If you do this then others will want the same...

If others need it, they can turn on the flag SLAB_MINIMIZE_WASTE too.

Mikulas