Re: [External] Re: [PATCH] mm/memory.c: Introduce non-atomic __{Set,Clear}PageSwapCache

["Xu, Yanfei" <yanfei.xu@windriver.com>]

On 10/20/20 9:08 PM, Muchun Song wrote:
> On Tue, Oct 20, 2020 at 7:51 PM Xu, Yanfei <yanfei.xu@windriver.com> wrote:
>>
>>
>>
>> On 10/19/20 10:58 PM, Muchun Song wrote:
>>> On Mon, Oct 19, 2020 at 8:31 PM Michal Hocko <mhocko@suse.com> wrote:
>>>>
>>>> On Mon 19-10-20 18:15:20, Muchun Song wrote:
>>>>> For the exclusive reference page, the non-atomic operations is enough,
>>>>> so replace them to non-atomic operations.
>>>>
>>>> I do expect you do not see any difference in runtime and this is mostly
>>>> driven by the code reading, right? Being explicit about this in the code
>>>> would be preferred.
>>>
>>> Yeah, just code reading.And the set_bit and __set_bit is actually different
>>> on some architectures. Thanks.
>>>
>>>>
>>>> No objection to the change.
>>>>
>>>>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>>>>
>>>> With an improved changelog
>>>> Acked-by: Michal Hocko <mhocko@suse.com>
>>>>
>>>>> ---
>>>>>    include/linux/page-flags.h | 2 ++
>>>>>    mm/memory.c                | 4 ++--
>>>>>    2 files changed, 4 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>>>>> index fbbb841a9346..ec039dde5e4b 100644
>>>>> --- a/include/linux/page-flags.h
>>>>> +++ b/include/linux/page-flags.h
>>>>> @@ -401,6 +401,8 @@ static __always_inline int PageSwapCache(struct page *page)
>>>>>    }
>>>>>    SETPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)
>>>>>    CLEARPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)
>>>>> +__SETPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)
>>>>> +__CLEARPAGEFLAG(SwapCache, swapcache, PF_NO_TAIL)
>>>>>    #else
>>>>>    PAGEFLAG_FALSE(SwapCache)
>>>>>    #endif
>>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>>> index 2d267ef6621a..02dd62da26e0 100644
>>>>> --- a/mm/memory.c
>>>>> +++ b/mm/memory.c
>>>>> @@ -3128,10 +3128,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>>>>>                                 set_page_private(page, entry.val);
>>>>>
>>>>>                                 /* Tell memcg to use swap ownership records */
>>>>> -                             SetPageSwapCache(page);
>>>>> +                             __SetPageSwapCache(page);
>>
>> Good evening, Muchun. I found there are still some places could be
>> replaced with __SetPageSwapCache（）. Such as shmem_replace_page（）, why
> 
> Yeah, thanks for your suggestion.
> 
>> PG_locked has been set before SetPageSwapCache（） is involved.
> 
> In this case, It doesn't matter whether PG_locked is set before
> SetPageSwapCache.
> 
Sorry for this mistake. PG_locked is used for disk I/O.
>>
>> Would you please to check the rest places? :)
> 
> Ok, I'll take a look. Thanks.
> 
>>
>> Thanks
>>
>> Acked-by: Yanfei Xu <yanfei.xu@windriver.com>
>>
>>>>>                                 err = mem_cgroup_charge(page, vma->vm_mm,
>>>>>                                                         GFP_KERNEL);
>>>>> -                             ClearPageSwapCache(page);
>>>>> +                             __ClearPageSwapCache(page);
>>>>>                                 if (err) {
>>>>>                                         ret = VM_FAULT_OOM;
>>>>>                                         goto out_page;
>>>>> --
>>>>> 2.20.1
>>>>>
>>>>
>>>> --
>>>> Michal Hocko
>>>> SUSE Labs
>>>
>>>
>>>
> 
> 
> 
> --
> Yours,
> Muchun
>