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

zhongjinji
2025-02-26T02:41:41Z

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