Re: [PATCH v3 1/3] mm/gup: restrict CMA region by using allocation scope API

[Vlastimil Babka]

On 7/31/20 9:35 AM, js1304@xxxxxxxxx wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> 
> We have well defined scope API to exclude CMA region.
> Use it rather than manipulating gfp_mask manually. With this change,
> we can now restore __GFP_MOVABLE for gfp_mask like as usual migration
> target allocation. It would result in that the ZONE_MOVABLE is also
> searched by page allocator. For hugetlb, gfp_mask is redefined since
> it has a regular allocation mask filter for migration target.
> __GPF_NOWARN is added to hugetlb gfp_mask filter since a new user for
> gfp_mask filter, gup, want to be silent when allocation fails.
> 
> Note that this can be considered as a fix for the commit 9a4e9f3b2d73
> ("mm: update get_user_pages_longterm to migrate pages allocated from
> CMA region"). However, "Fixes" tag isn't added here since it is just
> suboptimal but it doesn't cause any problem.
> 
> Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  include/linux/hugetlb.h |  2 ++
>  mm/gup.c                | 17 ++++++++---------
>  2 files changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 6b9508d..2660b04 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -708,6 +708,8 @@ static inline gfp_t htlb_modify_alloc_mask(struct hstate *h, gfp_t gfp_mask)
>  	/* Some callers might want to enfoce node */
>  	modified_mask |= (gfp_mask & __GFP_THISNODE);
>  
> +	modified_mask |= (gfp_mask & __GFP_NOWARN);
> +
>  	return modified_mask;
>  }
>  
> diff --git a/mm/gup.c b/mm/gup.c
> index a55f1ec..3990ddc 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1601,10 +1601,12 @@ static struct page *new_non_cma_page(struct page *page, unsigned long private)
>  	 * Trying to allocate a page for migration. Ignore allocation
>  	 * failure warnings. We don't force __GFP_THISNODE here because
>  	 * this node here is the node where we have CMA reservation and
> -	 * in some case these nodes will have really less non movable
> +	 * in some case these nodes will have really less non CMA
>  	 * allocation memory.
> +	 *
> +	 * Note that CMA region is prohibited by allocation scope.
>  	 */
> -	gfp_t gfp_mask = GFP_USER | __GFP_NOWARN;
> +	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_NOWARN;
>  
>  	if (PageHighMem(page))
>  		gfp_mask |= __GFP_HIGHMEM;
> @@ -1612,6 +1614,8 @@ static struct page *new_non_cma_page(struct page *page, unsigned long private)
>  #ifdef CONFIG_HUGETLB_PAGE
>  	if (PageHuge(page)) {
>  		struct hstate *h = page_hstate(page);
> +
> +		gfp_mask = htlb_modify_alloc_mask(h, gfp_mask);
>  		/*
>  		 * We don't want to dequeue from the pool because pool pages will
>  		 * mostly be from the CMA region.
> @@ -1626,11 +1630,6 @@ static struct page *new_non_cma_page(struct page *page, unsigned long private)
>  		 */
>  		gfp_t thp_gfpmask = GFP_TRANSHUGE | __GFP_NOWARN;
>  
> -		/*
> -		 * Remove the movable mask so that we don't allocate from
> -		 * CMA area again.
> -		 */
> -		thp_gfpmask &= ~__GFP_MOVABLE;
>  		thp = __alloc_pages_node(nid, thp_gfpmask, HPAGE_PMD_ORDER);
>  		if (!thp)
>  			return NULL;
> @@ -1773,7 +1772,6 @@ static long __gup_longterm_locked(struct mm_struct *mm,
>  				     vmas_tmp, NULL, gup_flags);
>  
>  	if (gup_flags & FOLL_LONGTERM) {
> -		memalloc_nocma_restore(flags);
>  		if (rc < 0)
>  			goto out;
>  
> @@ -1786,9 +1784,10 @@ static long __gup_longterm_locked(struct mm_struct *mm,
>  
>  		rc = check_and_migrate_cma_pages(mm, start, rc, pages,
>  						 vmas_tmp, gup_flags);
> +out:
> +		memalloc_nocma_restore(flags);
>  	}
>  
> -out:
>  	if (vmas_tmp != vmas)
>  		kfree(vmas_tmp);
>  	return rc;
>