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SubjectRe: [External] Re: [PATCH] mm/memory.c: Introduce non-atomic __{Set,Clear}PageSwapCache
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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
PG_locked has been set before SetPageSwapCache() is involved.

Would you please to check the rest places? :)

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
>
>
>

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