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SubjectRe: [v4 PATCH 1/2] mm: swap: check if swap backing device is congested or not
On Thu, Jan 03, 2019 at 09:10:13AM -0800, Yang Shi wrote:
> How about the below description:
>
> The test with page_fault1 of will-it-scale (sometimes tracing may just show
> runtest.py that is the wrapper script of page_fault1), which basically
> launches NR_CPU threads to generate 128MB anonymous pages for each thread, 
> 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();

That's better, thanks!

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