linux-kernel - [PATCH v4 12/13] mm: memory: allow arch override for folio_zero

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Message-Id: <20250616052223.723982-13-ankur.a.arora@oracle.com>
Date: Sun, 15 Jun 2025 22:22:22 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Cc: akpm@...ux-foundation.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, mjguzik@...il.com, luto@...nel.org,
        peterz@...radead.org, acme@...nel.org, namhyung@...nel.org,
        tglx@...utronix.de, willy@...radead.org, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, ankur.a.arora@...cle.com
Subject: [PATCH v4 12/13] mm: memory: allow arch override for folio_zero_user()

folio_zero_user() is constrained to operate in a page-at-a-time
fashion because it handles CONFIG_HIGHMEM which means that the
pages in a folio might be mapped to a discontiguous kernel address
range.

In addition, cooperative preemption models (none, voluntary) force
zeroing of successive chunks to be interspersed with invocations
invocations of cond_resched().

Allow an architecture specific override.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 mm/memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 8eba595056fe..e769480b712a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7079,8 +7079,11 @@ static int clear_subpage(unsigned long addr, int idx, void *arg)
  * folio_zero_user - Zero a folio which will be mapped to userspace.
  * @folio: The folio to zero.
  * @addr_hint: The address will be accessed or the base address if uncelar.
+ *
+ * folio_zero_user() does page-at-a-time zeroing because it needs to handle
+ * CONFIG_HIGHMEM. Allow architecture override.
  */
-void folio_zero_user(struct folio *folio, unsigned long addr_hint)
+void __weak folio_zero_user(struct folio *folio, unsigned long addr_hint)
 {
 	unsigned int nr_pages = folio_nr_pages(folio);
 
-- 
2.31.1