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

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

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.