Re: [RFC PATCH v0] mm/slub: Let number of online CPUs determine the slub page order

Mel Gorman
2021-01-28T14:44:21Z

On Thu, Jan 28, 2021 at 02:57:10PM +0100, Michal Hocko wrote:
> On Thu 28-01-21 13:45:12, Mel Gorman wrote:
> [...]
> > So mostly this is down to the number of times SLUB calls into the page
> > allocator which only caches order-0 pages on a per-cpu basis. I do have
> > a prototype for a high-order per-cpu allocator but it is very rough --
> > high watermarks stop making sense, code is rough, memory needed for the
> > pcpu structures quadruples etc.
>
> Thanks this is really useful. But it really begs a question whether this
> is a general case or more an exception. And as such maybe we want to
> define high throughput caches which would gain a higher order pages to
> keep pace with allocation and reduce the churn or deploy some other
> techniques to reduce the direct page allocator involvement.

I don't think we want to define "high throughput caches" because it'll
be workload dependant and a game of whack-a-mole. If the "high throughput
cache" is a kmalloc cache for some set of workloads and one of the inode
caches or dcaches for another one, there will be no setting that is
universally good.

--
Mel Gorman
SUSE Labs