Re: writeback completion soft lockup BUG in folio_wake_bit()

[Matthew Wilcox <willy@infradead.org>]

On Mon, Oct 24, 2022 at 01:28:31PM -0700, Linus Torvalds wrote:
> 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?

I've been carrying a pair of patches in my tree to rip out the wait
bookmarks since March, waiting for me to write a userspace testcase to
reproduce the problem against v4.13 and then check it no longer does so
against v5.0.  Unfortunately, that hasn't happened.  I'm happy to add
Arechiga's Tested-by, and submit them to Andrew and have him bring them
into v6.2, since this doesn't seem urgent?