From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christoph Lameter <cl@gentwo.de>
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
Date: Wed, 10 Mar 2021 10:17:43 -0800 [thread overview]
Message-ID: <CAHk-=whJCPchWozS0-4gF8zJ+9SfRv3h7jCSmivr+fs+eJJuZA@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2103100757530.128125@gentwo.de>
On Tue, Mar 9, 2021 at 10:59 PM Christoph Lameter <cl@gentwo.de> wrote:
>
> >
> > it really looks like this might well have been very intentional
> > indeed. Or at least very beneficial for _some_ loads.
>
> 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.
I wonder if we might have a "try twice before failing" middle ground,
rather than break out on the very first cmpxchg failure (or continue
forever).
Yes, yes, it claims a "Fixes:", but the commit it claims to fix really
does explicitly _mention_ avoiding the loop in the commit message, and
this kernel test robot report very much implies that that original
commit was right, and the "fix" is wrong.
Jann - if you had other loads that showed problems, that would be
worth documenting.
And as mentioned, maybe having a _limited_ retry, rather than a
"continue for as long as there is contention" that clearly regresses
on this (perhaps odd) load?
But for now, I think the thing to do is revert.
Linus
prev parent reply other threads:[~2021-03-10 18:18 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-01 8:04 [mm, slub] 8ff60eb052: stress-ng.rawpkt.ops_per_sec -47.9% regression kernel test robot
2021-03-09 23:56 ` Linus Torvalds
2021-03-10 6:59 ` Christoph Lameter
2021-03-10 18:17 ` Linus Torvalds [this message]
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