linux-kernel - Re: [RFC v2] prctl: prctl(PR_SET_IDLE, PR_IDLE_MODE

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Date:   Sat, 18 Nov 2017 20:19:54 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Shawn Landden <slandden@...il.com>
Cc:     Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-api@...r.kernel.org
Subject: Re: [RFC v2] prctl: prctl(PR_SET_IDLE, PR_IDLE_MODE_KILLME), for
 stateless idle loops

On Fri, Nov 17, 2017 at 08:45:03PM -0800, Shawn Landden wrote:
> On Fri, Nov 3, 2017 at 2:09 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > On Thu 02-11-17 23:35:44, Shawn Landden wrote:
> > > 16 bytes per process is kinda spendy, but I want to keep
> > > lru behavior, which mem_score_adj does not allow. When a supervisor,
> > > like Android's user input is keeping track this can be done in
> > user-space.
> > > It could be pulled out of task_struct if an cross-indexing additional
> > > red-black tree is added to support pid-based lookup.
> >
> > This is still an abuse and the patch is wrong. We really do have an API
> > to use I fail to see why you do not use it.
> >
> When I looked at wait_queue_head_t it was 20 byes.

24 bytes actually; the compiler will add 4 bytes of padding between
the spinlock and the list_head.  But there's one for the entire system.
Then you add a 40 byte structure (wait_queue_entry) on the stack for each
sleeping process.  There's no per-process cost.