Re: [PATCH] mm/rmap: Move anon_vma initialization to anon_vma_ctor()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

+cc David, Liam

On Wed, Apr 16, 2025 at 09:34:30AM +0800, Ye Liu wrote:
>
> 在 2025/4/15 19:28, Harry Yoo 写道:
> > On Tue, Apr 15, 2025 at 05:25:48PM +0800, Ye Liu wrote:
> >> From: Ye Liu <liuye@kylinos.cn>
> >>
> >> Currently, some initialization of anon_vma is performed in
> >> anon_vma_alloc(). Move the initialization to anon_vma_ctor()
> >> so that all object setup is handled in one place.
> >>
> >> Signed-off-by: Ye Liu <liuye@kylinos.cn>
> >> ---
> > NACK unless the patch explains how the object's initial state
> > ('constructed state') is preserved between uses.
> >
> > anon_vma_ctor() is a slab constructor. That means it is called only once
> > when a slab (folio) is allocated, and not called again when an anon_vma
> > is allocated from an existing slab (folio). In other words it is not called
> > everytime an object allocated via kmem_cache_alloc() interface.
> Thank you for the feedback. You're absolutely right — I misunderstood
> how the slab constructor (ctor) works. I had assumed it would be called
> every time an object is allocated via kmem_cache_alloc(), but I now
> realize it is only called once when a new slab is initialized, not on
> every object allocation.
> > This patch looks very dangerous to me and makes me question whether you
> > tested it before submission.
> >
> Appreciate you catching this — and yes, I'll test it more thoroughly
> before submitting other patches.
>
> Drop it.
>
> Thanks,
> Ye
>

I agree with Harry's assessment, also this is something that needs to be cc'd to
other developers - I am more generally working on anon_vma at the moment and
this is vma-adjacent even if slab-ish :)

It isn't your fault that you didn't, we need a MAINTAINERS entry for this which
I will submit, but for any future revision, please do cc Harry, David, Liam,
Vlastimil + myself.

I should be sending a MAINTAINERS patch later today which should correct this
going forward!

Cheers, Lorenzo