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

[Muchun Song]

On Tue, Oct 20, 2020 at 7:51 PM Xu, Yanfei <yanfei.xu@xxxxxxxxxxxxx> wrote:
>
>
>
> On 10/19/20 10:58 PM, Muchun Song wrote:
> > On Mon, Oct 19, 2020 at 8:31 PM Michal Hocko <mhocko@xxxxxxxx> 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@xxxxxxxxxxxxx>
> >>
> >> With an improved changelog
> >> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> >>
> >>> ---
> >>>   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.

>
> Would you please to check the rest places? :)

Ok, I'll take a look. Thanks.

>
> Thanks
>
> Acked-by: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
>
> >>>                                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