linux-kernel - Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page

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Message-ID: <CA+55aFzy981a8Ab+89APi6Qnb9U9xap=0A6XNc+wZsAWngWPzA@mail.gmail.com>
Date:   Fri, 25 Aug 2017 17:31:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        Christopher Lameter <cl@...ux.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 v2] sched/wait: Introduce lock breaker in wake_up_page_bit

On Fri, Aug 25, 2017 at 4:03 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Let this be a lesson in just *how* little tested, and *how* crap that
> patch probably still is.

I haven't had time to look at it any more (trying to merge the pull
requests that came in today instead), but the more I think about it,
the more I think it was a mistake to do that page_wait_struct
allocation on the stack.

It made it way more fragile and complicated, having to rewrite things
so carefully. A simple slab cache would likely be a lot cleaner and
simpler.

So even if that thing can be made to work, it's probably not worth the pain.

               Linus