On Fri 29-01-21 10:46:15, Mike Kravetz wrote:
> On 1/28/21 2:15 PM, Andrew Morton wrote:
> > On Thu, 28 Jan 2021 14:00:29 -0800 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
> >>
> >> Michal suggested that comments describing synchronization be added for each
> >> flag. Since I did 'one patch per flag', that would be an update to each patch.
> >> Or, I could simply add a patch to update the comment block based on what you
> >> already have.
> >>
> >> Let me know what is best/easiest for you.
> >
> > I guess just one patch is best for reviewers. Then I'll split up into
> > a sprinkle of -fix patches if I'm feeling energetic ;)
>
> Here is a patch to update the comments for all those flags. It should
> apply on top of what is in your tree.
>
> From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Date: Fri, 29 Jan 2021 10:36:12 -0800
> Subject: [PATCH] huegtlb: add synchronization information for new hugetlb
> specific flags
>
> Adding comments, no functional change.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks Mike!
> ---
> include/linux/hugetlb.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index e5e6ffd55392..cf70795d2209 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -480,14 +480,24 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> * HPG_restore_reserve - Set when a hugetlb page consumes a reservation at
> * allocation time. Cleared when page is fully instantiated. Free
> * routine checks flag to restore a reservation on error paths.
> + * Synchronization: Examined or modified by code that knows it has
> + * the only reference to page. i.e. After allocation but before use
> + * or when the page is being freed.
> * HPG_migratable - Set after a newly allocated page is added to the page
> * cache and/or page tables. Indicates the page is a candidate for
> * migration.
> + * Synchronization: Initially set after new page allocation with no
> + * locking. When examined and modified during migration processing
> + * (isolate, migrate, putback) the hugetlb_lock is held.
> * HPG_temporary - - Set on a page that is temporarily allocated from the buddy
> * allocator. Typically used for migration target pages when no pages
> * are available in the pool. The hugetlb free page path will
> * immediately free pages with this flag set to the buddy allocator.
> + * Synchronization: Can be set after huge page allocation from buddy when
> + * code knows it has only reference. All other examinations and
> + * modifications require hugetlb_lock.
> * HPG_freed - Set when page is on the free lists.
> + * Synchronization: hugetlb_lock held for examination and modification.
> */
> enum hugetlb_page_flags {
> HPG_restore_reserve = 0,
> --
> 2.29.2
>
--
Michal Hocko
SUSE Labs
