[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20200331153450.GM30449@dhcp22.suse.cz>
Date: Tue, 31 Mar 2020 17:34:50 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Joel Fernandes <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
rcu@...r.kernel.org, willy@...radead.org, peterz@...radead.org,
neilb@...e.com, vbabka@...e.cz, mgorman@...e.de,
Andrew Morton <akpm@...ux-foundation.org>,
Josh Triplett <josh@...htriplett.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free
memory pattern
On Tue 31-03-20 10:58:06, Joel Fernandes wrote:
[...]
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 4be763355c9fb..965deefffdd58 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3149,7 +3149,7 @@ static inline struct rcu_head *attach_rcu_head_to_object(void *obj)
> >
> > if (!ptr)
> > ptr = kmalloc(sizeof(unsigned long *) +
> > - sizeof(struct rcu_head), GFP_ATOMIC | __GFP_NOWARN);
> > + sizeof(struct rcu_head), GFP_MEMALLOC);
>
> Just to add, the main requirements here are:
> 1. Allocation should be bounded in time.
> 2. Allocation should try hard (possibly tapping into reserves)
> 3. Sleeping is Ok but should not affect the time bound.
__GFP_ATOMIC | __GFP_HIGH is the way to get an additional access to
memory reserves regarless of the sleeping status.
Using __GFP_MEMALLOC is quite dangerous because it can deplete _all_ the
memory. What does prevent the above code path to do that?
If a partial access to reserves is sufficient then why the existing
modifiers (mentioned above are not sufficient?
--
Michal Hocko
SUSE Labs
Powered by blists - more mailing lists