linux-kernel - Re: [PATCH 03/10] proc, oom_adj: extract oom_score

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Date:	Wed, 22 Jun 2016 11:17:12 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"'Michal Hocko'" <mhocko@...nel.org>
Cc:	"'Oleg Nesterov'" <oleg@...hat.com>,
	"'linux-kernel'" <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH 03/10] proc, oom_adj: extract oom_score_adj setting into a helper


> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index 968d5ea06e62..a6a8fbdd5a1b 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -1037,7 +1037,47 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count,
> > >  	return simple_read_from_buffer(buf, count, ppos, buffer, len);
> > >  }
> > >
> > > -static DEFINE_MUTEX(oom_adj_mutex);
> > > +static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
> > > +{
> > > +	static DEFINE_MUTEX(oom_adj_mutex);
> >
> > Writers are not excluded for readers!
> > Is this a hot path?
> 
> I am not sure I follow you question. This is a write path... Who would
> be the reader?
> 
Currently oom_adj_read() and oom_adj_write() are serialized with 
task->sighand->siglock, and in this work oom_adj_mutex is introduced to
only keep writers in hose.

Plus, oom_adj_write() and oom_badness() are currently serialized 
with task->alloc_lock, and they may be handled in subsequent patches.

thanks
Hillf