linux-kernel - [PATCH 6/7] mm/hugetlb: Drop vma_has

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Message-ID: <20241201212240.533824-7-peterx@redhat.com>
Date: Sun,  1 Dec 2024 16:22:39 -0500
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: Rik van Riel <riel@...riel.com>,
	Breno Leitao <leitao@...ian.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	peterx@...hat.com,
	Muchun Song <muchun.song@...ux.dev>,
	Oscar Salvador <osalvador@...e.de>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Naoya Horiguchi <nao.horiguchi@...il.com>,
	Ackerley Tng <ackerleytng@...gle.com>
Subject: [PATCH 6/7] mm/hugetlb: Drop vma_has_reserves()

After the previous cleanup, vma_has_reserves() is mostly an empty helper
except that it says "use reserve count" is inverted meaning from "needs a
global reserve count", which is still true.

To avoid confusions on having two inverted ways to ask the same question,
always use the gbl_chg everywhere, and drop the function.

When at it, rename "chg" to "gbl_chg" in dequeue_hugetlb_folio_vma().  It
might be helpful for readers to see that the "chg" here is the global
reserve count, not the vma resv count.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 mm/hugetlb.c | 23 ++++++-----------------
 1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b7e16b3c4e67..10251ef3289a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1246,16 +1246,6 @@ void clear_vma_resv_huge_pages(struct vm_area_struct *vma)
 	hugetlb_dup_vma_private(vma);
 }
 
-/* Returns true if the VMA has associated reserve pages */
-static bool vma_has_reserves(long chg)
-{
-	/*
-	 * Now "chg" has all the conditions considered for whether we
-	 * should use an existing reservation.
-	 */
-	return chg == 0;
-}
-
 static void enqueue_hugetlb_folio(struct hstate *h, struct folio *folio)
 {
 	int nid = folio_nid(folio);
@@ -1341,7 +1331,7 @@ static unsigned long available_huge_pages(struct hstate *h)
 
 static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 				struct vm_area_struct *vma,
-				unsigned long address, long chg)
+				unsigned long address, long gbl_chg)
 {
 	struct folio *folio = NULL;
 	struct mempolicy *mpol;
@@ -1350,11 +1340,10 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 	int nid;
 
 	/*
-	 * A child process with MAP_PRIVATE mappings created by their parent
-	 * have no page reserves. This check ensures that reservations are
-	 * not "stolen". The child may still get SIGKILLed
+	 * gbl_chg==1 means the allocation requires a new page that was not
+	 * reserved before.  Making sure there's at least one free page.
 	 */
-	if (!vma_has_reserves(chg) && !available_huge_pages(h))
+	if (gbl_chg && !available_huge_pages(h))
 		goto err;
 
 	gfp_mask = htlb_alloc_mask(h);
@@ -1372,7 +1361,7 @@ static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
 		folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask,
 							nid, nodemask);
 
-	if (folio && vma_has_reserves(chg)) {
+	if (folio && !gbl_chg) {
 		folio_set_hugetlb_restore_reserve(folio);
 		h->resv_huge_pages--;
 	}
@@ -3023,7 +3012,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 		if (!folio)
 			goto out_uncharge_cgroup;
 		spin_lock_irq(&hugetlb_lock);
-		if (vma_has_reserves(gbl_chg)) {
+		if (!gbl_chg) {
 			folio_set_hugetlb_restore_reserve(folio);
 			h->resv_huge_pages--;
 		}
-- 
2.47.0