linux-kernel - Re: [PATCH 1/2] sched/wait: Break up long wake list walk

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Date:   Wed, 23 Aug 2017 16:30:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk

On Wed, Aug 23, 2017 at 11:17 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Aug 23, 2017 at 8:58 AM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
>>
>> Will you still consider the original patch as a fail safe mechanism?
>
> I don't think we have much choice, although I would *really* want to
> get this root-caused rather than just papering over the symptoms.

Oh well. Apparently we're not making progress on that, so I looked at
the patch again.

Can we fix it up a bit? In particular, the "bookmark_wake_function()"
thing added no value, and definitely shouldn't have been exported.
Just use NULL instead.

And the WAITQUEUE_WALK_BREAK_CNT thing should be internal to
__wake_up_common(), not in some common header file. Again, there's no
value in exporting it to anybody else.

And doing

                if (curr->flags & WQ_FLAG_BOOKMARK)

looks odd, when we just did

                unsigned flags = curr->flags;

one line earlier, so that can be just simplified.

So can you test that simplified version of the patch? I'm attaching my
suggested edited patch, but you may just want to do those changes
directly to your tree instead.

Hmm?

               Linus

View attachment "patch.diff" of type "text/plain" (5018 bytes)