linux-kernel - [RFC PATCH v2 17/51] mm: hugetlb: Cleanup interpretation of gbl_chg in alloc_hugetlb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <cbdec587dec5ee10de4e4596d158c871e9630cac.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:41:56 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: kvm@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	x86@...nel.org, linux-fsdevel@...r.kernel.org
Cc: ackerleytng@...gle.com, aik@....com, ajones@...tanamicro.com, 
	akpm@...ux-foundation.org, amoorthy@...gle.com, anthony.yznaga@...cle.com, 
	anup@...infault.org, aou@...s.berkeley.edu, bfoster@...hat.com, 
	binbin.wu@...ux.intel.com, brauner@...nel.org, catalin.marinas@....com, 
	chao.p.peng@...el.com, chenhuacai@...nel.org, dave.hansen@...el.com, 
	david@...hat.com, dmatlack@...gle.com, dwmw@...zon.co.uk, 
	erdemaktas@...gle.com, fan.du@...el.com, fvdl@...gle.com, graf@...zon.com, 
	haibo1.xu@...el.com, hch@...radead.org, hughd@...gle.com, ira.weiny@...el.com, 
	isaku.yamahata@...el.com, jack@...e.cz, james.morse@....com, 
	jarkko@...nel.org, jgg@...pe.ca, jgowans@...zon.com, jhubbard@...dia.com, 
	jroedel@...e.de, jthoughton@...gle.com, jun.miao@...el.com, 
	kai.huang@...el.com, keirf@...gle.com, kent.overstreet@...ux.dev, 
	kirill.shutemov@...el.com, liam.merwick@...cle.com, 
	maciej.wieczor-retman@...el.com, mail@...iej.szmigiero.name, maz@...nel.org, 
	mic@...ikod.net, michael.roth@....com, mpe@...erman.id.au, 
	muchun.song@...ux.dev, nikunj@....com, nsaenz@...zon.es, 
	oliver.upton@...ux.dev, palmer@...belt.com, pankaj.gupta@....com, 
	paul.walmsley@...ive.com, pbonzini@...hat.com, pdurrant@...zon.co.uk, 
	peterx@...hat.com, pgonda@...gle.com, pvorel@...e.cz, qperret@...gle.com, 
	quic_cvanscha@...cinc.com, quic_eberman@...cinc.com, 
	quic_mnalajal@...cinc.com, quic_pderrin@...cinc.com, quic_pheragu@...cinc.com, 
	quic_svaddagi@...cinc.com, quic_tsoni@...cinc.com, richard.weiyang@...il.com, 
	rick.p.edgecombe@...el.com, rientjes@...gle.com, roypat@...zon.co.uk, 
	rppt@...nel.org, seanjc@...gle.com, shuah@...nel.org, steven.price@....com, 
	steven.sistare@...cle.com, suzuki.poulose@....com, tabba@...gle.com, 
	thomas.lendacky@....com, usama.arif@...edance.com, vannapurve@...gle.com, 
	vbabka@...e.cz, viro@...iv.linux.org.uk, vkuznets@...hat.com, 
	wei.w.wang@...el.com, will@...nel.org, willy@...radead.org, 
	xiaoyao.li@...el.com, yan.y.zhao@...el.com, yilun.xu@...el.com, 
	yuzenghui@...wei.com, zhiquan1.li@...el.com
Subject: [RFC PATCH v2 17/51] mm: hugetlb: Cleanup interpretation of gbl_chg
 in alloc_hugetlb_folio()

The comment before dequeuing a folio explains that if gbl_chg == 0, a
reservation exists for the allocation.

In addition, if a vma reservation exists, there's no need to get a
reservation from the subpool, and gbl_chg was set to 0.

This patch replaces both of that with code: subpool_reservation_exists
defaults to false, and if a vma reservation does not exist, a
reservation is sought from the subpool.

Then, the existence of a reservation, whether in the vma or subpool,
is summarized into reservation_exists, which is then used to determine
whether to dequeue a folio.

Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
Change-Id: I52130a0bf9f33e07d320a446cdb3ebfddd9de658
---
 mm/hugetlb.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b843e869496f..597f2b9f62b5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2999,8 +2999,10 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 {
 	struct hugepage_subpool *spool = subpool_vma(vma);
 	struct hstate *h = hstate_vma(vma);
+	bool subpool_reservation_exists;
+	bool reservation_exists;
 	struct folio *folio;
-	long retval, gbl_chg;
+	long retval;
 	map_chg_state map_chg;
 	int ret, idx;
 	struct hugetlb_cgroup *h_cg = NULL;
@@ -3036,17 +3038,16 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	 * that the allocation will not exceed the subpool limit.
 	 * Or if it can get one from the pool reservation directly.
 	 */
+	subpool_reservation_exists = false;
 	if (map_chg) {
-		gbl_chg = hugepage_subpool_get_pages(spool, 1);
-		if (gbl_chg < 0)
+		int npages_req = hugepage_subpool_get_pages(spool, 1);
+
+		if (npages_req < 0)
 			goto out_end_reservation;
-	} else {
-		/*
-		 * If we have the vma reservation ready, no need for extra
-		 * global reservation.
-		 */
-		gbl_chg = 0;
+
+		subpool_reservation_exists = npages_req == 0;
 	}
+	reservation_exists = !map_chg || subpool_reservation_exists;
 
 	/*
 	 * If this allocation is not consuming a per-vma reservation,
@@ -3065,13 +3066,8 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 
 	spin_lock_irq(&hugetlb_lock);
 
-	/*
-	 * gbl_chg == 0 indicates a reservation exists for the allocation - so
-	 * try dequeuing a page. If there are available_huge_pages(), try using
-	 * them!
-	 */
 	folio = NULL;
-	if (!gbl_chg || available_huge_pages(h))
+	if (reservation_exists || available_huge_pages(h))
 		folio = dequeue_hugetlb_folio(h, vma, addr);
 
 	if (!folio) {
@@ -3089,7 +3085,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	 * Either dequeued or buddy-allocated folio needs to add special
 	 * mark to the folio when it consumes a global reservation.
 	 */
-	if (!gbl_chg) {
+	if (reservation_exists) {
 		folio_set_hugetlb_restore_reserve(folio);
 		h->resv_huge_pages--;
 	}
-- 
2.49.0.1045.g170613ef41-goog