On Fri, Oct 21, 2022 at 04:36:22PM +0000, James Houghton wrote:
> This allows us to add more data into the shared structure, which we will
> use to store whether or not HGM is enabled for this VMA or not, as HGM
> is only available for shared mappings.
>
> It may be better to include HGM as a VMA flag instead of extending the
> VMA lock structure.
>
> Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
> ---
> include/linux/hugetlb.h | 4 +++
> mm/hugetlb.c | 65 +++++++++++++++++++++--------------------
> 2 files changed, 37 insertions(+), 32 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index a899bc76d677..534958499ac4 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -121,6 +121,10 @@ struct hugetlb_vma_lock {
> struct vm_area_struct *vma;
> };
>
> +struct hugetlb_shared_vma_data {
> + struct hugetlb_vma_lock vma_lock;
> +};
How about add a comment above hugetlb_vma_lock showing how it should be
used correctly? We lacked documents on the lock for pmd sharing
protections, now if to reuse the same lock for HGM pgtables I think some
doc will definitely help.
To summarize, I think so far it means:
- Read lock needed when one wants to stablize VM_SHARED pgtables (covers
both pmd shared pgtables or hgm low-level pgtables)
- Write lock needed when one wants to release VM_SHARED pgtable pages
(covers both pmd unshare or releasing hgm low-level pgtables)
Or something like that.
--
Peter Xu
