From: Joel Fernandes <joel@joelfernandes.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, rcu <rcu@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Peter Zijlstra <peterz@infradead.org>,
Neil Brown <neilb@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
Josh Triplett <josh@joshtriplett.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free memory pattern
Date: Wed, 1 Apr 2020 10:45:56 -0400 [thread overview]
Message-ID: <CAEXW_YTpXojYiskwiqZGHpT45v3xZYhuvy0CubaeyB3fMrmw7g@mail.gmail.com> (raw)
In-Reply-To: <20200401131426.GN3772@suse.de>
On Wed, Apr 1, 2020 at 9:14 AM Mel Gorman <mgorman@suse.de> wrote:
>
> On Wed, Apr 01, 2020 at 09:23:59AM +0200, Michal Hocko wrote:
> > > Can you suggest what prevents other users of GFP_MEMALLOC from doing that
> > > also?
> >
> > There is no explicit mechanism which is indeed unfortunate. The only
> > user real user of the flag is Swap over NFS AFAIK. I have never dared to
> > look into details on how the complete reserves depletion is prevented.
> > Mel would be much better fit here.
> >
>
> It's "prevented" by the fact that every other memory allocation request
> that is not involved with reclaiming memory gets stalled in the allocator
> with only the swap subsystem making any progress until the machine
> recovers. Potentially only kswapd is still running until the system
> recovers if stressed hard enough.
>
> The naming is terrible but is mased on kswapd's use of the PF_MEMALLOC
> flag. For swap-over-nfs, GFP_MEMALLOC saying "this allocation request is
> potentially needed for kswapd to make forward progress and not freeze".
>
> I would not be comfortable with kfree_rcu() doing the same thing because
> there can be many callers in parallel and it's freeing slab objects.
> Swap over NFS should free at least one page, freeing a slab object is
> not guaranteed to free anything.
Got it Mel. Just to clarify to the onlooker. It seemed to fit the
pattern that's why I proposed it as RFC, I was never sure it was the
right approach -- I just proposed it for discussion-sake because I
thought it was worth talking about at least. It was not even merged in
my tree, was just RFC.
Thanks Mel for clarifying the usage of the flag.
- Joel
next prev parent reply other threads:[~2020-04-01 14:46 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-31 13:16 [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free memory pattern Joel Fernandes (Google)
2020-03-31 14:04 ` Uladzislau Rezki
2020-03-31 15:09 ` Joel Fernandes
2020-03-31 16:01 ` Uladzislau Rezki
2020-03-31 17:02 ` Uladzislau Rezki
2020-03-31 17:49 ` Paul E. McKenney
2020-03-31 18:30 ` Joel Fernandes
2020-04-01 12:25 ` Uladzislau Rezki
2020-04-01 13:47 ` Paul E. McKenney
2020-04-01 18:16 ` Uladzislau Rezki
2020-04-01 18:26 ` Paul E. McKenney
2020-04-01 18:37 ` Uladzislau Rezki
2020-04-01 18:54 ` Paul E. McKenney
2020-04-01 19:05 ` Uladzislau Rezki
2020-04-01 19:34 ` Paul E. McKenney
2020-04-01 19:35 ` Uladzislau Rezki
2020-03-31 14:58 ` Joel Fernandes
2020-03-31 15:34 ` Michal Hocko
2020-03-31 16:01 ` Joel Fernandes
2020-03-31 22:19 ` NeilBrown
2020-04-01 3:25 ` Joel Fernandes
2020-04-01 4:52 ` NeilBrown
2020-04-01 7:23 ` Michal Hocko
2020-04-01 11:14 ` joel
2020-04-01 12:05 ` Michal Hocko
2020-04-01 13:14 ` Mel Gorman
2020-04-01 14:45 ` Joel Fernandes [this message]
2020-03-31 16:12 ` Uladzislau Rezki
2020-04-01 7:09 ` Michal Hocko
2020-04-01 12:32 ` Uladzislau Rezki
2020-04-01 12:55 ` Michal Hocko
2020-04-01 13:08 ` Uladzislau Rezki
2020-04-01 13:15 ` Michal Hocko
2020-04-01 13:22 ` Uladzislau Rezki
2020-04-01 15:28 ` Michal Hocko
2020-04-01 15:46 ` Uladzislau Rezki
2020-04-01 15:57 ` Paul E. McKenney
2020-04-01 16:10 ` Michal Hocko
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