Re: SLUB: percpu partial object count is highly inaccurate, causing some memory wastage and maybe also worse tail latencies?

From: Michal Hocko
Date: Mon Jan 18 2021 - 06:05:14 EST

On Thu 14-01-21 10:27:40, Vlastimil Babka wrote:
> On 1/12/21 5:35 PM, Christoph Lameter wrote:
> > On Tue, 12 Jan 2021, Jann Horn wrote:
> >
> >> [This is not something I intend to work on myself. But since I
> >> stumbled over this issue, I figured I should at least document/report
> >> it, in case anyone is willing to pick it up.]
> >
> > Well yeah all true. There is however a slabinfo tool that has an -s option
> > to shrink all slabs.
> >
> > slabinfo -s
> >
> > So you could put that somewhere that executes if the system is
> > idle or put it into cron or so.
> Hm this would be similar to recommending a periodical echo > drop_caches
> operation. We actually discourage from that (and yeah, some tools do that, and
> we now report those in dmesg). I believe the kernel should respond to memory
> pressure and not OOM prematurely by itself, including SLUB.

Absolutely agreed! Partial caches are a very deep internal
implementation detail of the allocator and admin has no bussiness into
fiddling with that. This would only lead to more harm than good.
Comparision to drop_caches is really exact!

Michal Hocko