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

[Qi Zheng <zhengqi.arch@bytedance.com>]

On 2024/12/15 02:29, Yu Zhao wrote:
> On Sat, Dec 14, 2024 at 2:03 AM Qi Zheng <zhengqi.arch@bytedance.com> wrote:
>>
>> This reverts commit 2f3443770437e49abc39af26962d293851cbab6d.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> Bloating struct pt_lock is unnecessary. Glad to see it's reverted.

Indeed!

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

Thanks! Once the review of this patch series is completed, we can simply
drop "mm: pgtable: make ptlock be freed by RCU" from mm tree.

> 
> 
>> ---
>>   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
>>