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

[Xu, Yanfei]

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 
PG_locked has been set before SetPageSwapCache（） is involved.

Would you please to check the rest places? :)

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