linux-kernel - Re: [PATCH 01/12] Revert "mm: pgtable: make ptlock be freed by RCU"

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Message-ID: <CAOUHufaKRXJA=vZucoJMmgQw264LSxWuTtNcFQMLD7UNz_6wyw@mail.gmail.com>
Date: Sat, 14 Dec 2024 11:29:35 -0700
From: Yu Zhao <yuzhao@...gle.com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: peterz@...radead.org, tglx@...utronix.de, david@...hat.com, 
	jannh@...gle.com, hughd@...gle.com, willy@...radead.org, 
	muchun.song@...ux.dev, vbabka@...nel.org, lorenzo.stoakes@...cle.com, 
	akpm@...ux-foundation.org, rientjes@...gle.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/12] Revert "mm: pgtable: make ptlock be freed by RCU"

On Sat, Dec 14, 2024 at 2:03 AM Qi Zheng <zhengqi.arch@...edance.com> wrote:
>
> This reverts commit 2f3443770437e49abc39af26962d293851cbab6d.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>

Bloating struct pt_lock is unnecessary. Glad to see it's reverted.

Acked-by: Yu Zhao <yuzhao@...gle.com>


> ---
>  include/linux/mm.h       |  2 +-
>  include/linux/mm_types.h |  9 +--------
>  mm/memory.c              | 22 ++++++----------------
>  3 files changed, 8 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e7902980439cc..5e73e53c34e9e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2988,7 +2988,7 @@ void ptlock_free(struct ptdesc *ptdesc);
>
>  static inline spinlock_t *ptlock_ptr(struct ptdesc *ptdesc)
>  {
> -       return &(ptdesc->ptl->ptl);
> +       return ptdesc->ptl;
>  }
>  #else /* ALLOC_SPLIT_PTLOCKS */
>  static inline void ptlock_cache_init(void)
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index df8f5152644ec..5d8779997266e 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -434,13 +434,6 @@ FOLIO_MATCH(flags, _flags_2a);
>  FOLIO_MATCH(compound_head, _head_2a);
>  #undef FOLIO_MATCH
>
> -#if ALLOC_SPLIT_PTLOCKS
> -struct pt_lock {
> -       spinlock_t ptl;
> -       struct rcu_head rcu;
> -};
> -#endif
> -
>  /**
>   * struct ptdesc -    Memory descriptor for page tables.
>   * @__page_flags:     Same as page flags. Powerpc only.
> @@ -485,7 +478,7 @@ struct ptdesc {
>         union {
>                 unsigned long _pt_pad_2;
>  #if ALLOC_SPLIT_PTLOCKS
> -               struct pt_lock *ptl;
> +               spinlock_t *ptl;
>  #else
>                 spinlock_t ptl;
>  #endif
> diff --git a/mm/memory.c b/mm/memory.c
> index d9af83dd86bbf..83765632e20b0 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -7041,34 +7041,24 @@ static struct kmem_cache *page_ptl_cachep;
>
>  void __init ptlock_cache_init(void)
>  {
> -       page_ptl_cachep = kmem_cache_create("page->ptl", sizeof(struct pt_lock), 0,
> +       page_ptl_cachep = kmem_cache_create("page->ptl", sizeof(spinlock_t), 0,
>                         SLAB_PANIC, NULL);
>  }
>
>  bool ptlock_alloc(struct ptdesc *ptdesc)
>  {
> -       struct pt_lock *pt_lock;
> +       spinlock_t *ptl;
>
> -       pt_lock = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
> -       if (!pt_lock)
> +       ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
> +       if (!ptl)
>                 return false;
> -       ptdesc->ptl = pt_lock;
> +       ptdesc->ptl = ptl;
>         return true;
>  }
>
> -static void ptlock_free_rcu(struct rcu_head *head)
> -{
> -       struct pt_lock *pt_lock;
> -
> -       pt_lock = container_of(head, struct pt_lock, rcu);
> -       kmem_cache_free(page_ptl_cachep, pt_lock);
> -}
> -
>  void ptlock_free(struct ptdesc *ptdesc)
>  {
> -       struct pt_lock *pt_lock = ptdesc->ptl;
> -
> -       call_rcu(&pt_lock->rcu, ptlock_free_rcu);
> +       kmem_cache_free(page_ptl_cachep, ptdesc->ptl);
>  }
>  #endif
>
> --
> 2.20.1
>