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Date:   Wed, 10 Mar 2021 18:27:53 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Jim Newsome <jnewsome@torproject.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Christian Brauner <christian@brauner.io>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] do_wait: make PIDTYPE_PID case O(1) instead of O(n)
Message-ID: <20210310172752.GA8973@redhat.com>
References: <20210309203919.15920-1-jnewsome@torproject.org>
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On 03/09, Jim Newsome wrote:
>
> do_wait is an internal function used to implement waitpid, waitid,
> wait4, etc. To handle the general case, it does an O(n) linear scan of
> the thread group's children and tracees.
>
> This patch adds a special-case when waiting on a pid to skip these scans
> and instead do an O(1) lookup. This improves performance when waiting on
> a pid from a thread group with many children and/or tracees.
>
> Signed-off-by: James Newsome <jnewsome@torproject.org>

Reviewed-by: Oleg Nesterov <oleg@redhat.com>