Re: [PATCH 0/1] mm: Remove the SLAB allocator

[Christopher Lameter]

On Wed, 17 Apr 2019, Jesper Dangaard Brouer wrote:

> I do think SLUB have a number of pathological cases where SLAB is
> faster.  If was significantly more difficult to get good bulk-free
> performance for SLUB.  SLUB is only fast as long as objects belong to
> the same page.  To get good bulk-free performance if objects are
> "mixed", I coded this[1] way-too-complex fast-path code to counter
> act this (joined work with Alex Duyck).

Right. SLUB usually compensates for that with superior allocation
performance.

> > It's, of course, worth thinking about other pathological cases too.
> > Workloads that cause large allocations is one. Workloads that cause lots
> > of slab cache shrinking is another.
>
> I also worry about long uptimes when SLUB objects/pages gets too
> fragmented... as I said SLUB is only efficient when objects are
> returned to the same page, while SLAB is not.

??? Why would SLUB pages get more fragmented? SLUB has fragmentation
prevention methods that SLAB does not have.