On Thu, Jan 28, 2021 at 02:57:10PM +0100, Michal Hocko wrote:

On Thu 28-01-21 13:45:12, Mel Gorman wrote:
[...]

quoted

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