linux-kernel - Re: [PATCH 2/3] mm, meminit: Recalculate pcpu batch and high limits after init completes

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Message-ID: <20191020093235.GL3321@techsingularity.net>
Date:   Sun, 20 Oct 2019 10:32:35 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Borislav Petkov <bp@...en8.de>, Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mm, meminit: Recalculate pcpu batch and high limits
 after init completes

On Fri, Oct 18, 2019 at 06:40:24PM -0700, Andrew Morton wrote:
> On Fri, 18 Oct 2019 15:09:59 +0100 Mel Gorman <mgorman@...hsingularity.net> wrote:
> 
> > > > Cc: stable@...r.kernel.org # v4.15+
> > > 
> > > Hmm, are you sure about 4.15? Doesn't this go all the way down to
> > > deferred initialization? I do not see any recent changes on when
> > > setup_per_cpu_pageset is called.
> > > 
> > 
> > No, I'm not 100% sure. It looks like this was always an issue from the
> > code but did not happen on at least one 4.12-based distribution kernel for
> > reasons that are non-obvious. Either way, the tag should have been "v4.1+"
> 
> I could mark
> 
> mm-pcp-share-common-code-between-memory-hotplug-and-percpu-sysctl-handler.patch
> mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
> 
> as Cc: <stable@...r.kernel.org>	[4.1+]
> 

That would be fine.

> But for backporting purposes it's a bit cumbersome that [2/3] is the
> important patch.  I think I'll switch the ordering so that
> mm-meminit-recalculate-pcpu-batch-and-high-limits-after-init-completes.patch
> is the first patch and the other two can be queued for 5.5-rc1, OK?
> 

It might be easier to simply collapse patch 1 and 2 together. They were
only split to make the review easier and to avoid two relatively big
changes in one patch.

> Also, is a Reported-by:Matt appropriate here?
> 

I don't object but I'm not actually sure who reported this first. I think
it was Thomas who talked to Boris about an EPYC performance issue, who
talked to Matt thinking it might be a scheduler issue who identified it
was my problem :P

-- 
Mel Gorman
SUSE Labs