linux-kernel - Re: [RFC PATCH] mm: silence soft lockups from unlock

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Date:   Mon, 3 Aug 2020 10:56:17 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [RFC PATCH] mm: silence soft lockups from unlock_page

On Mon, Aug 3, 2020 at 6:14 AM Michal Hocko <mhocko@...e.com> wrote:
>
> I hope I got it right and this is the latest version of your patches. Btw.
> do you still think that increasing PAGE_WAIT_TABLE_BITS is reasonable.

I suspect it's still very reasonable, but I'd love to have numbers for it.

> In the meantime I have learned that the customer suffering from the
> issue is very unlikely to reboot the machine anytime soon or even
> willing to test a non-trivial patch. We do not own any machine which
> exhibit this problem unfortunately. So it is quite unlikely I can
> help with testing.

Ok.

> Also does it make sense to put this into mmotm tree for a while to get a
> larger testing coverage?

Well, I did the 5.8 release yesterday, so I just put it in the tree
for the 5.9 merge window - I've been running it locally since I posted
it, and while Hugh couldn't prove it improved anything, his results
certainly also didn't say it was bad.

So anybody that tests my top-of-tree will be testing that thing now,
which is likely more than linux-next or mmotm gets (outside of build
testing and the robots).

Of course, I don't know how many people run my development tree,
particularly during the busy merge window, but hey, at worst it will
be in the next linux-next that way. At best, it's not just me, but a
number of other developers.

                   Linus