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From: Michal Hocko <mhocko@kernel.org>
Newsgroups: linux.kernel
Subject: Re: [PATCH 03/10] proc, oom_adj: extract oom_score_adj setting into  a helper
Date: Tue, 21 Jun 2016 14:20:01 +0200
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On Tue 21-06-16 17:27:57, Hillf Danton wrote:
> > 
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > Currently we have two proc interfaces to set oom_score_adj. The legacy
> > /proc/<pid>/oom_adj and /proc/<pid>/oom_score_adj which both have their
> > specific handlers. Big part of the logic is duplicated so extract the
> > common code into __set_oom_adj helper. Legacy knob still expects some
> > details slightly different so make sure those are handled same way - e.g.
> > the legacy mode ignores oom_score_adj_min and it warns about the usage.
> > 
> > This patch shouldn't introduce any functional changes.
> > 
> > Acked-by: Oleg Nesterov <oleg@redhat.com>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> >  fs/proc/base.c | 94 +++++++++++++++++++++++++++-------------------------------
> >  1 file changed, 43 insertions(+), 51 deletions(-)
> > 
> > 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?
-- 
Michal Hocko
SUSE Labs