linux-kernel - Re: [PATCH 2/4] signal: Make flush_sigqueue() use free

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Date:   Fri, 22 Mar 2019 14:12:01 -0400
From:   Waiman Long <longman@...hat.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        selinux@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH 2/4] signal: Make flush_sigqueue() use free_q to release
 memory

On 03/22/2019 01:50 PM, Christopher Lameter wrote:
> On Fri, 22 Mar 2019, Waiman Long wrote:
>
>> I am looking forward to it.
> There is also alrady rcu being used in these paths. kfree_rcu() would not
> be enough? It is an estalished mechanism that is mature and well
> understood.
>
In this case, the memory objects are from kmem caches, so they can't
freed using kfree_rcu().

There are certainly overhead using the kfree_rcu(), or a
kfree_rcu()-like mechanism. Also I think the actual freeing is done at
SoftIRQ context which can be a problem if there are too many memory
objects to free.

I think what Oleg is trying to do is probably the most efficient way.

Cheers,
Longman