linux-kernel - Re: [PATCH v9 11/17] mm: replace vm_lock and detached flag with a reference count

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Message-ID: <CAJuCfpG3OMHpBg5BFcXH5935aYD9v7ON8dQrHr1t9HS3m_htvQ@mail.gmail.com>
Date: Mon, 13 Jan 2025 13:16:41 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: akpm@...ux-foundation.org, peterz@...radead.org, willy@...radead.org, 
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Subject: Re: [PATCH v9 11/17] mm: replace vm_lock and detached flag with a
 reference count

On Sun, Jan 12, 2025 at 6:38 PM Wei Yang <richard.weiyang@...il.com> wrote:
>
> On Fri, Jan 10, 2025 at 08:25:58PM -0800, Suren Baghdasaryan wrote:
> > static inline void vma_end_read(struct vm_area_struct *vma) {}
> >@@ -908,12 +948,8 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
> >       vma->vm_mm = mm;
> >       vma->vm_ops = &vma_dummy_vm_ops;
> >       INIT_LIST_HEAD(&vma->anon_vma_chain);
> >-#ifdef CONFIG_PER_VMA_LOCK
> >-      /* vma is not locked, can't use vma_mark_detached() */
> >-      vma->detached = true;
> >-#endif
> >       vma_numab_state_init(vma);
> >-      vma_lock_init(vma);
> >+      vma_lock_init(vma, false);
>
> vma_init(vma, mm)
>   memset(vma, 0, sizeof(*vma))
>   ...
>   vma_lock_init(vma, false);
>
> It looks the vm_refcnt must be reset.
>
> BTW, I don't figure out why we want to skip the reset of vm_refcnt. Is this
> related to SLAB_TYPESAFE_BY_RCU?

Earlier memset(vma, 0, sizeof(*vma)) already zeroes the entire
structure, so vm_refcnt is already 0 and does not need to be reset
again.

>
> > }
> >
>
> --
> Wei Yang
> Help you, Help me