linux-kernel - Re: [PATCH 2/4] mm: move per-vma lock into vm_area

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Message-ID: <CAJuCfpGOjnwXuDh4y3O=8NzRtGFwMS8qEpmiYMSaC9JbWFLfZg@mail.gmail.com>
Date: Tue, 12 Nov 2024 08:58:05 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: akpm@...ux-foundation.org, willy@...radead.org, liam.howlett@...cle.com, 
	lorenzo.stoakes@...cle.com, mhocko@...e.com, hannes@...xchg.org, 
	mjguzik@...il.com, oliver.sang@...el.com, mgorman@...hsingularity.net, 
	david@...hat.com, peterx@...hat.com, oleg@...hat.com, dave@...olabs.net, 
	paulmck@...nel.org, brauner@...nel.org, dhowells@...hat.com, hdanton@...a.com, 
	hughd@...gle.com, minchan@...gle.com, jannh@...gle.com, 
	shakeel.butt@...ux.dev, souravpanda@...gle.com, pasha.tatashin@...een.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 2/4] mm: move per-vma lock into vm_area_struct

On Tue, Nov 12, 2024 at 8:08 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Tue, Nov 12, 2024 at 7:57 AM Vlastimil Babka <vbabka@...e.cz> wrote:
> >
> > On 11/11/24 21:55, Suren Baghdasaryan wrote:
> > > @@ -511,7 +476,6 @@ void __vm_area_free(struct vm_area_struct *vma)
> > >  {
> > >       vma_numab_state_free(vma);
> > >       free_anon_vma_name(vma);
> > > -     vma_lock_free(vma);
> > >       kmem_cache_free(vm_area_cachep, vma);
> > >  }
> >
> > Have you investigated if this allows to perform vma_numab_state_free() and
> > free_anon_vma_name() immediately, and only kfree_rcu() the vma itself,
> > instead of performing all this in a call_rcu() callback?
>
> Yes, it should be fine to free them immediately. lock_vma_under_rcu()
> does not use neither vma->numab_state, nor vma->anon_name.
>
> >
> > Of course if we succeed converting vma's to SLAB_TYPESAFE_RCU this immediate
> > freeing of numab state and anon_vma_name would be implied, but maybe it's an
> > useful intermediate step on its own.
>
> I'm thinking maybe I should post SLAB_TYPESAFE_RCU conversion before
> anything else. It's simple and quite uncontroversial. I will probably
> do that today.

Uh, I forgot that I can't post SLAB_TYPESAFE_RCU until I eliminate
this vma_lock_free() call inside __vm_area_free(). So, I have to
bundle moving vm_lock into vm_area_struct with SLAB_TYPESAFE_RCU.