[PATCH] mm/page_alloc: make the maximum number of highatomic pageblocks resizable

[<zhongjinji@honor.com>]

From: zhongjinji <zhongjinji@honor.com>

In the past, nr_reserved_highatomic was considered to be part of
unusable_free when there was no ALLOC_RESERVES flag. To prevent
unusable_free from being too large, it is reasonable to set a
fixed maximum highatomic value.

Even if the maximum number of highatomic pageblocks is set to be larger,
unusable_free may not increase, since Yu Zhao provided the modification
about nr_free_highatomic in
https://lore.kernel.org/all/20241028182653.3420139-1-yuzhao@google.com/T/#u

More highatomic pageblocks are beneficial for the successful allocation
of high-order page, which is helpful in some devices. Therefore, use
highatomic_reserve_ratio to adjust the maximum number of highatomic
pageblocks.

Signed-off-by: zhongjinji <zhongjinji@honor.com>
---
 mm/page_alloc.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 579789600a3c..dbdce6a0f694 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -273,6 +273,7 @@ int min_free_kbytes = 1024;
 int user_min_free_kbytes = -1;
 static int watermark_boost_factor __read_mostly = 15000;
 static int watermark_scale_factor = 10;
+static int highatomic_reserve_ratio = 10;
 
 /* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */
 int movable_zone;
@@ -2046,7 +2047,8 @@ static void reserve_highatomic_pageblock(struct page *page, int order,
 	 */
 	if ((zone_managed_pages(zone) / 100) < pageblock_nr_pages)
 		return;
-	max_managed = ALIGN((zone_managed_pages(zone) / 100), pageblock_nr_pages);
+	max_managed = ALIGN((zone_managed_pages(zone) * highatomic_reserve_ratio / 1000),
+		      pageblock_nr_pages);
 	if (zone->nr_reserved_highatomic >= max_managed)
 		return;
 
@@ -6199,6 +6201,13 @@ static const struct ctl_table page_alloc_sysctl_table[] = {
 		.mode		= 0644,
 		.proc_handler	= percpu_pagelist_high_fraction_sysctl_handler,
 		.extra1		= SYSCTL_ZERO,
+	},
+		.procname	= "highatomic_reserve_ratio",
+		.data		= &highatomic_reserve_ratio,
+		.maxlen		= sizeof(highatomic_reserve_ratio),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
 	},
 	{
 		.procname	= "lowmem_reserve_ratio",
-- 
2.17.1