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Date:   Wed, 27 Apr 2022 12:21:47 -0300
From:   Marcelo Tosatti <mtosatti@redhat.com>
To:     Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc:     Minchan Kim <minchan@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>
Subject: Re: [RFC PATCH 0/6] Drain remote per-cpu directly
Message-ID: <Ymlfi2vas76Tgk4W@fuller.cnet>
References: <20220420095906.27349-1-mgorman@techsingularity.net>
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 <cf861ff3bf106b71994886cad7c4570b6ce9af0d.camel@redhat.com>
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On Tue, Apr 26, 2022 at 01:06:12PM +0200, Nicolas Saenz Julienne wrote:
> On Mon, 2022-04-25 at 15:58 -0700, Minchan Kim wrote:
> > On Wed, Apr 20, 2022 at 10:59:00AM +0100, Mel Gorman wrote:
> > > This series has the same intent as Nicolas' series "mm/page_alloc: Remote
> > > per-cpu lists drain support" -- avoid interference of a high priority
> > > task due to a workqueue item draining per-cpu page lists. While many
> > > workloads can tolerate a brief interruption, it may be cause a real-time
> > > task runnning on a NOHZ_FULL CPU to miss a deadline and at minimum,
> > > the draining in non-deterministic.
> > 
> > Yeah, the non-deterministic is a problem. I saw the kworker-based draining
> > takes 100+ms(up to 300ms observed) sometimes in alloc_contig_range if CPUs
> > are heavily loaded.
> > 
> > I am not sure Nicolas already observed. it's not only problem of
> > per_cpu_pages but it is also lru_pvecs (pagevec) draining.
> > Do we need to introduce similar(allow remote drainning with spin_lock)
> > solution for pagevec?
> 
> Yes, I'm aware of the lru problem. I'll start working on it too once we're done
> with the page allocator (and if no-one beats me to it). That said, I don't know
> if we can apply the exact same approach, the devil is in the details. :)

I think one necessary step for that (adding spinlock to protect per-CPU
lru_pvecs) would be to find a suitable testcase.

Mel, do you have anything in mind ?


> 
> -- 
> Nicol?s S?enz
> 
>