linux-kernel - Re: [RFC PATCH 0/5] Remove dependency on congestion

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Date:   Mon, 20 Sep 2021 12:42:44 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Linux-MM <linux-mm@...ck.org>, NeilBrown <neilb@...e.de>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Rik van Riel <riel@...riel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/5] Remove dependency on congestion_wait in mm/

On Mon, Sep 20, 2021 at 09:54:31AM +0100, Mel Gorman wrote:
> This has been lightly tested only and the testing was useless as the
> relevant code was not executed. The workload configurations I had that
> used to trigger these corner cases no longer work (yey?) and I'll need
> to implement a new synthetic workload. If someone is aware of a realistic
> workload that forces reclaim activity to the point where reclaim stalls
> then kindly share the details.

The stereeotypical "stalling on I/O" problem is to plug in one of the
crap USB drives you were given at a trade show and simply
	dd if=/dev/zero of=/dev/sdb
	sync

You can also set up qemu to have extremely slow I/O performance:
https://serverfault.com/questions/675704/extremely-slow-qemu-storage-performance-with-qcow2-images