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Fri, 5 Dec 2025 14:44:06 -0500 (EST) From: Kiryl Shutsemau To: Andrew Morton , Muchun Song Cc: David Hildenbrand , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Matthew Wilcox , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Usama Arif , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Kiryl Shutsemau Subject: [PATCH 08/11] hugetlb: Remove VMEMMAP_SYNCHRONIZE_RCU Date: Fri, 5 Dec 2025 19:43:44 +0000 Message-ID: <20251205194351.1646318-9-kas@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251205194351.1646318-1-kas@kernel.org> References: <20251205194351.1646318-1-kas@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 7mq9rzftzjndojsopkrbcb3s6agznjpf X-Rspamd-Queue-Id: 56A8B4000E X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1764963849-165180 X-HE-Meta: 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 syPgTaOj JFSMbaxPcOuK2wk2KbSTJqIka8ChMI8ibF0MF4VUUK1YgeMx2SfWMT8wxhvqmgasen6qR7WZF1+/H+uvuTztNqFtwqlzgj1GEb2AJwANeiJnoQHV3gTkTcEAQ3G3DooUATDVqotJI3IzWTwGYJCRQhhm56x8qtQXKzwG6AXFajvfzK72hKsYmZJdMrrGqTJ9m8woVwrHM2GaJacoQHrU/gztVvbmcJSDSYo9PYrgNMEe8bm2rdDdAF5oABZ4IsPvEJTcwJBGuEM8rHAEqDitcDZYce1sx8tgc0CW1icT8XIkT3/HXyJV+HtZUaw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Fake heads no longer exist, so there is no reason to synchronize them with page_ref_add_unless(). Remove the flag and the synchronization with synchronize_rcu() that is gated by it. Signed-off-by: Kiryl Shutsemau --- mm/hugetlb_vmemmap.c | 20 ++++---------------- 1 file changed, 4 insertions(+), 16 deletions(-) diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 2543bdbcae20..0f142e4eafb9 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -48,8 +48,6 @@ struct vmemmap_remap_walk { #define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0) /* Skip the TLB flush when we remap the PTE */ #define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1) -/* synchronize_rcu() to avoid writes from page_ref_add_unless() */ -#define VMEMMAP_SYNCHRONIZE_RCU BIT(2) unsigned long flags; }; @@ -423,9 +421,6 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h, if (!folio_test_hugetlb_vmemmap_optimized(folio)) return 0; - if (flags & VMEMMAP_SYNCHRONIZE_RCU) - synchronize_rcu(); - vmemmap_start = (unsigned long)folio; vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h); @@ -457,7 +452,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h, */ int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio) { - return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU); + return __hugetlb_vmemmap_restore_folio(h, folio, 0); } /** @@ -480,14 +475,11 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h, struct folio *folio, *t_folio; long restored = 0; long ret = 0; - unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU; + unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH; list_for_each_entry_safe(folio, t_folio, folio_list, lru) { if (folio_test_hugetlb_vmemmap_optimized(folio)) { ret = __hugetlb_vmemmap_restore_folio(h, folio, flags); - /* only need to synchronize_rcu() once for each batch */ - flags &= ~VMEMMAP_SYNCHRONIZE_RCU; - if (ret) break; restored++; @@ -558,8 +550,6 @@ static int __hugetlb_vmemmap_optimize_folio(struct hstate *h, static_branch_inc(&hugetlb_optimize_vmemmap_key); - if (flags & VMEMMAP_SYNCHRONIZE_RCU) - synchronize_rcu(); /* * Very Subtle * If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed @@ -621,7 +611,7 @@ void hugetlb_vmemmap_optimize_folio(struct hstate *h, struct folio *folio) { LIST_HEAD(vmemmap_pages); - __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU); + __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, 0); free_vmemmap_page_list(&vmemmap_pages); } @@ -649,7 +639,7 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h, struct folio *folio; int nr_to_optimize; LIST_HEAD(vmemmap_pages); - unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU; + unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH; nr_to_optimize = 0; list_for_each_entry(folio, folio_list, lru) { @@ -702,8 +692,6 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h, int ret; ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags); - /* only need to synchronize_rcu() once for each batch */ - flags &= ~VMEMMAP_SYNCHRONIZE_RCU; /* * Pages to be freed may have been accumulated. If we -- 2.51.2