Re: slab: introduce the flag SLAB_MINIMIZE_WASTE

[Mikulas Patocka]

On Tue, 17 Apr 2018, Christopher Lameter wrote:

> On Mon, 16 Apr 2018, Mikulas Patocka wrote:
> 
> > dm-bufio deals gracefully with allocation failure, because it preallocates
> > some buffers with vmalloc, but other subsystems may not deal with it and
> > they cound return ENOMEM randomly or misbehave in other ways. So, the
> > "SLAB_MINIMIZE_WASTE" flag is also saying that the allocation may fail and
> > the caller is prepared to deal with it.
> >
> > The slub subsystem does actual fallback to low-order when the allocation
> > fails (it allows different order for each slab in the same cache), but
> > slab doesn't fallback and you get NULL if higher-order allocation fails.
> > So, SLAB_MINIMIZE_WASTE is needed for slab because it will just randomly
> > fail with higher order.
> 
> Fix Slab instead of adding a flag that is only useful for one allocator?

Slab assumes that all slabs have the same order, so it's not so easy to 
fix it.

Mikulas