linux-kernel - Re: [PATCH 1/2] mm/slub: Introduce two counters for the partial objects

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Message-ID: <alpine.DEB.2.22.394.2008071258020.55871@www.lameter.com>
Date:   Fri, 7 Aug 2020 13:02:43 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Pekka Enberg <penberg@...il.com>
cc:     Vlastimil Babka <vbabka@...e.cz>,
        Xunlei Pang <xlpang@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wen Yang <wenyang@...ux.alibaba.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Roman Gushchin <guro@...com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 1/2] mm/slub: Introduce two counters for the partial
 objects

On Fri, 7 Aug 2020, Pekka Enberg wrote:

> I think we can just default to the counters. After all, if I
> understood correctly, we're talking about up to 100 ms time period
> with IRQs disabled when count_partial() is called. As this is
> triggerable from user space, that's a performance bug whatever way you
> look at it.


Well yes under extreme conditions and this is only happening for sysfs
counter retrieval.

There could be other solutions to this. This solution here is penalizing
evertu hotpath slab allocation for the sake of relatively infrequently
used counter monitoring. There the possibility of not traversing the list
ande simply estimating the value based on the number of slab pages
allocated on that node.

> Christoph, others, any objections?

Obviously .... ;-)