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Date:   Wed, 10 Mar 2021 07:59:51 +0100 (CET)
From:   Christoph Lameter <cl@gentwo.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
cc:     kernel test robot <oliver.sang@intel.com>,
        Jann Horn <jannh@google.com>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Pekka Enberg <penberg@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        kernel test robot <lkp@intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Feng Tang <feng.tang@intel.com>, zhengjun.xing@intel.com
Subject: Re: [mm, slub] 8ff60eb052: stress-ng.rawpkt.ops_per_sec -47.9%
 regression
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On Tue, 9 Mar 2021, Linus Torvalds wrote:

> So when you wrote:
>
>     However, the current code accidentally stops looking at the partial list
>     completely in that case.  Especially on kernels without CONFIG_NUMA set,
>     this means that get_partial() fails and new_slab_objects() falls back to
>     new_slab(), allocating new pages.  This could lead to an unnecessary
>     increase in memory fragmentation.
>
> it really looks like this might well have been very intentional
> indeed. Or at least very beneficial for _some_ loads.
>
> Comments?

Yes the thought was that adding an additional page when contention is
there on the page objects will increase possible concurrency while
avoiding locks and increase the ability to allocate / free concurrently
from a multitude of objects.