linux-kernel - Re: [RFC 2/2] mm/slub: prefer NUMA locality over slight memory saving on NUMA machines

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Date:   Tue, 8 Aug 2023 11:59:09 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Feng Tang <feng.tang@...el.com>,
        "Sang, Oliver" <oliver.sang@...el.com>,
        Jay Patel <jaypatel@...ux.ibm.com>,
        Binder Makin <merimus@...gle.com>, aneesh.kumar@...ux.ibm.com,
        tsahu@...ux.ibm.com, piyushs@...ux.ibm.com, fengwei.yin@...el.com,
        ying.huang@...el.com, lkp <lkp@...el.com>,
        "oe-lkp@...ts.linux.dev" <oe-lkp@...ts.linux.dev>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] mm/slub: prefer NUMA locality over slight memory saving
 on NUMA machines

On 8/7/23 10:39, Hyeonggon Yoo wrote:
> On Thu, Aug 3, 2023 at 11:54 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
> 
> Thank you for looking at it!
> 
> Yeah, it was a PoC for what I thought "oh, it might be useful"
> and definitely I will try to measure it.
> 
>> We could also postpone this until we have tried the percpu arrays
>> improvements discussed at LSF/MM.
> 
> Possibly, but can you please share your plans/opinions on it?

Here's the very first attempt :)
https://lore.kernel.org/linux-mm/20230808095342.12637-7-vbabka@suse.cz/

> I think one possible way is simply to allow the cpu freelist to be
> mixed by objects from different slabs

I didn't try that way, might be much trickier than it looks.

> if we want to minimize changes, Or introduce a per cpu array similar
> to what SLAB does now.

Yes.

> And one thing I'm having difficulty understanding is - what is the
> mind behind/or impact of managing objects
> on a slab basis, other than avoiding array queues in 2007?

"The mind" is Christoph's so I'll leave that question to him :)