Re: [External] Re: [PATCH v10 10/11] mm/hugetlb: Gather discrete indexes of tail page

[Muchun Song]

On Fri, Dec 18, 2020 at 5:06 PM Oscar Salvador <osalvador@xxxxxxx> wrote:
>
> On Thu, Dec 17, 2020 at 08:13:02PM +0800, Muchun Song wrote:
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 6c02f49959fd..78dd88dda857 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1360,7 +1360,7 @@ static inline void hwpoison_subpage_deliver(struct hstate *h, struct page *head)
> >       if (!PageHWPoison(head) || !free_vmemmap_pages_per_hpage(h))
> >               return;
> >
> > -     page = head + page_private(head + 4);
> > +     page = head + page_private(head + SUBPAGE_INDEX_HWPOISON);
> >
> >       /*
> >        * Move PageHWPoison flag from head page to the raw error page,
> > @@ -1379,7 +1379,7 @@ static inline void hwpoison_subpage_set(struct hstate *h, struct page *head,
> >               return;
> >
> >       if (free_vmemmap_pages_per_hpage(h)) {
> > -             set_page_private(head + 4, page - head);
> > +             set_page_private(head + SUBPAGE_INDEX_HWPOISON, page - head);
>
> Ok, I was too eager here.
>
> If CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is not set for whatever reason
> (e.g: CONFIG_MEMORY_HOTREMOVE is disabled), when you convert "+4"
> to its index (SUBPAGE_INDEX_HWPOISON), this will no longer build
> since we only define SUBPAGE_INDEX_HWPOISON when the config
> option CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set.

Yeah, it is my mistake. Thanks for pointing that out.

>
> Different things can be done to fix this:
>
> e.g:
>
>  - Define a two different hwpoison_subpage_{deliver,set}
>    and have them under
>    #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
>    ...
>    #else
>    ...
>    #endif
>
>  - Work it around as is with IS_ENABLED(CONFIG_HUGETLB_...
>  - Have a common entry and decide depending on whether
>    the config is enabled.
>
> I guess option #1 might be cleaner.

Thanks for your suggestion. I also prefer option #1.

>
> --
> Oscar Salvador
> SUSE L3



-- 
Yours,
Muchun