Re: [External] Re: [PATCH v12 12/13] mm/hugetlb: Gather discrete indexes of tail page

[Muchun Song]

On Thu, Jan 14, 2021 at 8:18 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> On 1/6/21 6:19 AM, Muchun Song wrote:
> > For HugeTLB page, there are more metadata to save in the struct page.
> > But the head struct page cannot meet our needs, so we have to abuse
> > other tail struct page to store the metadata. In order to avoid
> > conflicts caused by subsequent use of more tail struct pages, we can
> > gather these discrete indexes of tail struct page. In this case, it
> > will be easier to add a new tail page index later.
> >
> > There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
> > page structs that can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP,
> > so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> > ---
> >  include/linux/hugetlb.h        | 14 ++++++++++++++
> >  include/linux/hugetlb_cgroup.h | 15 +++++++++------
> >  mm/hugetlb.c                   | 25 ++++++++++++-------------
> >  mm/hugetlb_vmemmap.c           |  8 ++++++++
> >  4 files changed, 43 insertions(+), 19 deletions(-)
>
> My apologies!  I did not get to this patch in previous versions of the
> series.  My "RFC create hugetlb flags to consolidate state" was done
> before I even noticed your efforts here.
>
> At least we agree the metadata could be better organized. :)
>
> IMO, using page.private of the head page to consolidate flags will be
> easier to manage.  So, I would like to use that.

Agree. Using page.private to manage the page flag is a good
choice. When your RFC patch is applied, I will rebase it and
rework this patch.

>
> The BUILD_BUG_ON in this patch makes sense.
> --
> Mike Kravetz