Re: [PATCH v2 1/2] seqlock: Do the lockdep annotation before locking in do_write_seqcount_begin_nested()

Michal Hocko
2023-08-03T14:49:59Z

On Thu 03-08-23 22:18:10, Tetsuo Handa wrote:
> On 2023/07/31 23:25, Michal Hocko wrote:
> > On Sat 29-07-23 20:05:43, Tetsuo Handa wrote:
> >> On 2023/07/29 14:31, Tetsuo Handa wrote:
> >>> On 2023/07/28 0:10, Sebastian Andrzej Siewior wrote:
> >>>> On 2023-06-28 21:14:16 [+0900], Tetsuo Handa wrote:
> >>>>>> Anyway, please do not do this change only because of printk().
> >>>>>> IMHO, the current ordering is more logical and the printk() problem
> >>>>>> should be solved another way.
> >>>>>
> >>>>> Then, since [PATCH 1/2] cannot be applied, [PATCH 2/2] is automatically
> >>>>> rejected.
> >>>>
> >>>> My understanding is that this patch gets applied and your objection will
> >>>> be noted.
> >>>
> >>> My preference is that zonelist_update_seq is not checked by !__GFP_DIRECT_RECLAIM
> >>> allocations, which is a low-hanging fruit towards GFP_LOCKLESS mentioned at
> >>> https://lkml.kernel.org/r/ZG3+l4qcCWTPtSMD@dhcp22.suse.cz and
> >>> https://lkml.kernel.org/r/ZJWWpGZMJIADQvRS@dhcp22.suse.cz .
> >>>
> >>> Maybe we can defer checking zonelist_update_seq till retry check like below,
> >>> for this is really an infrequent event.
> >>>
> >>
> >> An updated version with comments added.
> >
> > Seriously, don't you see how hairy all this is? And for what? Nitpicking
> > something that doesn't seem to be a real problem in the first place?
>
> Seriously, can't you find "zonelist_update_seq is not checked by !__GFP_DIRECT_RECLAIM
> allocations, which is a low-hanging fruit towards GFP_LOCKLESS" !?

I do not think we have concluded that we want to support GFP_LOCKLESS.
This might be trivial straightforward now but it imposes some constrains
for future maintainability. So far we haven't heard about many usecases
where this would be needed and a single one is not sufficient IMHO.
--
Michal Hocko
SUSE Labs