Move the unit computation and make it a const. Also, clean up the
comment a little bit.

Use SZ_32M to define PROCESS_PAGES_NON_PREEMPT_BATCH instead
of hand coding the computation.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---

Hi Andrew

Could you fixup patch-7 "mm: folio_zero_user: clear page ranges" with
this patch?

Thanks
Ankur

---
 include/linux/mm.h |  2 +-
 mm/memory.c        | 20 ++++++++++----------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c1ff832c33b5..e8bb09816fbf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4238,7 +4238,7 @@ static inline void clear_pages(void *addr, unsigned int npages)
  * (See comment above clear_pages() for why preemption latency is a concern
  * here.)
  */
-#define PROCESS_PAGES_NON_PREEMPT_BATCH		(32 << (20 - PAGE_SHIFT))
+#define PROCESS_PAGES_NON_PREEMPT_BATCH		(SZ_32M >> PAGE_SHIFT)
 #else /* !clear_pages */
 /*
  * The architecture does not provide a clear_pages() implementation. Assume
diff --git a/mm/memory.c b/mm/memory.c
index 11ad1db61929..f80c67eba79f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -7240,19 +7240,19 @@ static inline int process_huge_page(
 static void clear_contig_highpages(struct page *page, unsigned long addr,
 				   unsigned int nr_pages)
 {
-	unsigned int i, unit, count;
-
-	might_sleep();
+	unsigned int i, count;
 	/*
-	 * When clearing we want to operate on the largest extent possible since
-	 * that allows for extent based architecture specific optimizations.
+	 * When clearing we want to operate on the largest extent possible to
+	 * allow for architecture specific extent based optimizations.
 	 *
-	 * However, since the clearing interfaces (clear_user_highpages(),
-	 * clear_user_pages(), clear_pages()), do not call cond_resched(), we
-	 * limit the batch size when running under non-preemptible scheduling
-	 * models.
+	 * However, since clear_user_highpages() (and primitives clear_user_pages(),
+	 * clear_pages()), do not call cond_resched(), limit the unit size when
+	 * running under non-preemptible scheduling models.
 	 */
-	unit = preempt_model_preemptible() ? nr_pages : PROCESS_PAGES_NON_PREEMPT_BATCH;
+	const unsigned int unit = preempt_model_preemptible() ?
+				   nr_pages : PROCESS_PAGES_NON_PREEMPT_BATCH;
+
+	might_sleep();
 
 	for (i = 0; i < nr_pages; i += count) {
 		cond_resched();
-- 
2.31.1