linux-kernel - Re: [RFC PATCH 0/6] Drain remote per-cpu directly

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Message-ID: <cf861ff3bf106b71994886cad7c4570b6ce9af0d.camel@redhat.com>
Date:   Tue, 26 Apr 2022 13:06:12 +0200
From:   Nicolas Saenz Julienne <nsaenzju@...hat.com>
To:     Minchan Kim <minchan@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     Marcelo Tosatti <mtosatti@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [RFC PATCH 0/6] Drain remote per-cpu directly

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. :)

-- 
Nicolás Sáenz