Re: writeback completion soft lockup BUG in folio_wake_bit()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Mon, Oct 24, 2022 at 1:13 PM Dan Williams <dan.j.williams@intel.com> wrote:
>
> Arechiga reports that his test case that failed "fast" before now ran
> for 28 hours without a soft lockup report with the proposed patches
> applied. So, I would consider those:
>
> Tested-by: Jesus Arechiga Lopez <jesus.a.arechiga.lopez@intel.com>

Ok, great.

I really like that patch myself (and obviously liked it back when it
was originally proposed), but I think it was always held back by the
fact that we didn't really have any hard data for it.

It does sound like we now very much have hard data for "the page
waitlist complexity is now a bigger problem than the historical
problem it tried to solve".

So I'll happily apply it. The only question is whether it's a "let's
do this for 6.2", or if it's something that we'd want to back-port
anyway, and might as well apply sooner rather than later as a fix.

I think that in turn then depends on just how artificial the test case
was. If the test case was triggered by somebody seeing problems in
real life loads, that would make the urgency a lot higher. But if it
was purely a synthetic test case with no accompanying "this is what
made us look at this" problem, it might be a 6.2 thing.

Arechiga?

Also, considering that Willy authored the patch (even if it's really
just a "remove this whole code logic"), maybe he has opinions? Willy?

                 Linus