linux-kernel - Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap

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Message-ID: <20180130075553.GM21609@dhcp22.suse.cz>
Date:   Tue, 30 Jan 2018 08:55:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "He, Roger" <Hongbo.He@....com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: Re: [PATCH] mm/swap: add function get_total_swap_pages to expose
 total_swap_pages

On Tue 30-01-18 02:56:51, He, Roger wrote:
> Hi Michal:
> 
> We need a API to tell TTM module the system totally has how many swap
> cache.  Then TTM module can use it to restrict how many the swap cache
> it can use to prevent triggering OOM.  For Now we set the threshold of
> swap size TTM used as 1/2 * total size and leave the rest for others
> use.

Why do you so much memory? Are you going to use TB of memory on large
systems? What about memory hotplug when the memory is added/released?
 
> But get_nr_swap_pages is the only API we can accessed from other
> module now.  It can't cover the case of the dynamic swap size
> increment.  I mean: user can use "swapon" to enable new swap file or
> swap disk dynamically or "swapoff" to disable swap space.

Exactly. Your scaling configuration based on get_nr_swap_pages or the
available memory simply sounds wrong.
-- 
Michal Hocko
SUSE Labs