linux-kernel - [PATCH v2 2/4] mm/gup: restrict CMA region by using allocation scope API

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Date:   Mon, 20 Jul 2020 13:56:16 +0900
From:   js1304@...il.com
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v2 2/4] mm/gup: restrict CMA region by using allocation scope API

From: Joonsoo Kim <iamjoonsoo.kim@....com>

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@...e.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 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 5daadae..bbd36a1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1619,10 +1619,12 @@ 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;
@@ -1630,6 +1632,8 @@ 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.
@@ -1644,11 +1648,6 @@ 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;
@@ -1794,7 +1793,6 @@ static long __gup_longterm_locked(struct task_struct *tsk,
 				     vmas_tmp, NULL, gup_flags);
 
 	if (gup_flags & FOLL_LONGTERM) {
-		memalloc_nocma_restore(flags);
 		if (rc < 0)
 			goto out;
 
@@ -1807,9 +1805,10 @@ static long __gup_longterm_locked(struct task_struct *tsk,
 
 		rc = check_and_migrate_cma_pages(tsk, mm, start, rc, pages,
 						 vmas_tmp, gup_flags);
+out:
+		memalloc_nocma_restore(flags);
 	}
 
-out:
 	if (vmas_tmp != vmas)
 		kfree(vmas_tmp);
 	return rc;
-- 
2.7.4