Re: [PATCH v4 4/5] mm: rename zone->lock to zone->_lock

[Dmitry Ilvokhin <d@ilvokhin.com>]

On Thu, Mar 05, 2026 at 10:27:07AM +0100, Vlastimil Babka (SUSE) wrote:
> On 3/4/26 16:13, SeongJae Park wrote:
> > On Wed, 4 Mar 2026 13:01:45 +0000 Dmitry Ilvokhin <d@ilvokhin.com> wrote:
> > 
> >> On Tue, Mar 03, 2026 at 05:50:34PM -0800, SeongJae Park wrote:
> >> > On Tue, 3 Mar 2026 14:25:55 +0000 Dmitry Ilvokhin <d@ilvokhin.com> wrote:
> >> > 
> >> > > On Mon, Mar 02, 2026 at 02:37:43PM -0800, Andrew Morton wrote:
> >> > > > On Mon, 2 Mar 2026 15:10:03 +0100 "Vlastimil Babka (SUSE)" <vbabka@kernel.org> wrote:
> >> > > > 
> >> > > > > On 2/27/26 17:00, Dmitry Ilvokhin wrote:
> >> > > > > > This intentionally breaks direct users of zone->lock at compile time so
> >> > > > > > all call sites are converted to the zone lock wrappers. Without the
> >> > > > > > rename, present and future out-of-tree code could continue using
> >> > > > > > spin_lock(&zone->lock) and bypass the wrappers and tracing
> >> > > > > > infrastructure.
> >> > > > > > 
> >> > > > > > No functional change intended.
> >> > > > > > 
> >> > > > > > Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> >> > > > > > Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
> >> > > > > > Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
> >> > > > > > Acked-by: SeongJae Park <sj@kernel.org>
> >> > > > > 
> >> > > > > I see some more instances of 'zone->lock' in comments in
> >> > > > > include/linux/mmzone.h and under Documentation/ but otherwise LGTM.
> >> > > > > 
> >> > > > 
> >> > > > I fixed (most of) that in the previous version but my fix was lost.
> >> > > 
> >> > > Thanks for the fixups, Andrew.
> >> > > 
> >> > > I still see a few 'zone->lock' references in Documentation remain on
> >> > > mm-new. This patch cleans them up, as noted by Vlastimil.
> >> > > 
> >> > > I'm happy to adjust this patch if anything else needs attention.
> >> > > 
> >> > > From 9142d5a8b60038fa424a6033253960682e5a51f4 Mon Sep 17 00:00:00 2001
> >> > > From: Dmitry Ilvokhin <d@ilvokhin.com>
> >> > > Date: Tue, 3 Mar 2026 06:13:13 -0800
> >> > > Subject: [PATCH] mm: fix remaining zone->lock references
> >> > > 
> >> > > Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
> >> > > ---
> >> > >  Documentation/mm/physical_memory.rst | 4 ++--
> >> > >  Documentation/trace/events-kmem.rst  | 8 ++++----
> >> > >  2 files changed, 6 insertions(+), 6 deletions(-)
> >> > > 
> >> > > diff --git a/Documentation/mm/physical_memory.rst b/Documentation/mm/physical_memory.rst
> >> > > index b76183545e5b..e344f93515b6 100644
> >> > > --- a/Documentation/mm/physical_memory.rst
> >> > > +++ b/Documentation/mm/physical_memory.rst
> >> > > @@ -500,11 +500,11 @@ General
> >> > >  ``nr_isolate_pageblock``
> >> > >    Number of isolated pageblocks. It is used to solve incorrect freepage counting
> >> > >    problem due to racy retrieving migratetype of pageblock. Protected by
> >> > > -  ``zone->lock``. Defined only when ``CONFIG_MEMORY_ISOLATION`` is enabled.
> >> > > +  ``zone_lock``. Defined only when ``CONFIG_MEMORY_ISOLATION`` is enabled.
> >> > 
> >> > Dmitry's original patch [1] was doing 's/zone->lock/zone->_lock/', which aligns
> >> > to my expectation.  But this patch is doing 's/zone->lock/zone_lock/'.  Same
> >> > for the rest of this patch.
> >> > 
> >> > I was initially thinking this is just a mistake, but I also found Andrew is
> >> > doing same change [2], so I'm bit confused.  Is this an intentional change?
> >> > 
> >> > [1] https://lore.kernel.org/d61500c5784c64e971f4d328c57639303c475f81.1772206930.git.d@ilvokhin.com
> >> > [2] https://lore.kernel.org/20260302143743.220eed4feb36d7572fe726cc@linux-foundation.org
> >> > 
> >> 
> >> Good catch, thanks for pointing this out, SJ.
> >> 
> >> Originally the mechanical rename was indeed zone->lock -> zone->_lock.
> >> However, in Documentation I intentionally switched references to
> >> zone_lock instead of zone->_lock. The reasoning is that _lock is now an
> >> internal implementation detail, and direct access is discouraged. The
> >> intended interface is via the zone_lock_*() / zone_unlock_*() wrappers,
> >> so referencing zone_lock in documentation felt more appropriate than
> >> mentioning the private struct field (zone->_lock).
> > 
> > Thank you for this nice and kind clarification, Dmitry!  I agree mentioning
> > zone_[un]lock_*() helpers instead of the hidden member (zone->_lock) can be
> > better.
> > 
> > But, I'm concerned if people like me might not aware the intention under
> > 'zone_lock'.  If there is a well-known convention that allows people to know it
> > is for 'zone_[un]lock_*()' helpers, making it more clear would be nice, in my
> > humble opinion.  If there is such a convention but I'm just missing it, please
> > ignore.  If I'm not, for eaxmaple,
> > 
> > "protected by ``zone->lock``" could be re-wrote to
> > "protected by ``zone_[un]lock_*()`` locking helpers" or,
> > "protected by zone lock helper functions (``zone_[un]lock_*()``)" ?
> > 
> >> 
> >> That said, I agree this creates inconsistency with the mechanical
> >> rename, and I'm happy to adjust either way: either consistently refer
> >> to the wrapper API, or keep documentation aligned with zone->_lock.
> >> 
> >> I slightly prefer referring to the wrapper API, but don't have a strong
> >> preference as long as we're consistent.
> > 
> > I also think both approaches are good.  But for the wrapper approach, I think
> > giving more contexts rather than just ``zone_lock`` to readers would be nice.
> 
> Grep tells me that we also have comments mentioning simply "zone lock", btw.
> And it's also a term used often in informal conversations. Maybe we could
> just standardize on that in comments/documentations as it's easier to read.
> Discovering that the field is called _lock and that wrappers should be used,
> is hopefully not that difficult.

Thanks for the suggestion, Vlastimil. That sounds reasonable to me as
well. I'll update the comments and documentation to consistently use
"zone lock".