linux-kernel - Re: [v4 PATCH 1/2] mm: swap: check if swap backing device is congested or not

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Date:   Wed, 2 Jan 2019 15:00:54 -0800
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     ying.huang@...el.com, tim.c.chen@...el.com, minchan@...nel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v4 PATCH 1/2] mm: swap: check if swap backing device is
 congested or not

On Sun, Dec 30, 2018 at 12:49:34PM +0800, Yang Shi wrote:
> The test on my virtual machine with congested HDD shows long tail
> latency is reduced significantly.
> 
> Without the patch
>  page_fault1_thr-1490  [023]   129.311706: funcgraph_entry:      #57377.796 us |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.369103: funcgraph_entry:        5.642us   |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.369119: funcgraph_entry:      #1289.592 us |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.370411: funcgraph_entry:        4.957us   |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.370419: funcgraph_entry:        1.940us   |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.378847: funcgraph_entry:      #1411.385 us |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.380262: funcgraph_entry:        3.916us   |  do_swap_page();
>  page_fault1_thr-1490  [023]   129.380275: funcgraph_entry:      #4287.751 us |  do_swap_page();
> 
> With the patch
>       runtest.py-1417  [020]   301.925911: funcgraph_entry:      #9870.146 us |  do_swap_page();
>       runtest.py-1417  [020]   301.935785: funcgraph_entry:        9.802us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935799: funcgraph_entry:        3.551us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935806: funcgraph_entry:        2.142us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935853: funcgraph_entry:        6.938us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935864: funcgraph_entry:        3.765us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935871: funcgraph_entry:        3.600us   |  do_swap_page();
>       runtest.py-1417  [020]   301.935878: funcgraph_entry:        7.202us   |  do_swap_page();

Hi Yang, I guess runtest.py just calls page_fault1_thr?  Being explicit about
this may improve the changelog for those unfamiliar with will-it-scale.

May also be useful to name will-it-scale and how it was run (#thr, runtime,
system cpus/memory/swap) for more context.