linux-kernel - [PATCH v3] mm/page_alloc: simplify lowmem

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Message-ID: <20250815024509.37900-1-ye.liu@linux.dev>
Date: Fri, 15 Aug 2025 10:45:09 +0800
From: Ye Liu <ye.liu@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>
Cc: Ye Liu <liuye@...inos.cn>,
	Johannes Weiner <hannes@...xchg.org>,
	Zi Yan <ziy@...dia.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] mm/page_alloc: simplify lowmem_reserve max calculation

From: Ye Liu <liuye@...inos.cn>

Use max() to find the maximum lowmem_reserve value and min_t() to
cap it to managed_pages in calculate_totalreserve_pages(), instead
of open-coding the comparisons. No functional change.

Signed-off-by: Ye Liu <liuye@...inos.cn>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Zi Yan <ziy@...dia.com>

Changes in v3:
- max = min_t(unsigned long, max, managed_pages);
- Link to v2:https://lore.kernel.org/all/20250815023500.36893-1-ye.liu@linux.dev/

Changes in v2:
- Drop unnecessary braces
- Replace "if (max > managed_pages)" with min_t()
- Link to v1:https://lore.kernel.org/all/20250814090053.22241-1-ye.liu@linux.dev/
---
 mm/page_alloc.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 64872214bc7d..eff07323987c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6235,16 +6235,13 @@ static void calculate_totalreserve_pages(void)
 			unsigned long managed_pages = zone_managed_pages(zone);
 
 			/* Find valid and maximum lowmem_reserve in the zone */
-			for (j = i; j < MAX_NR_ZONES; j++) {
-				if (zone->lowmem_reserve[j] > max)
-					max = zone->lowmem_reserve[j];
-			}
+			for (j = i; j < MAX_NR_ZONES; j++)
+				max = max(max, zone->lowmem_reserve[j]);
 
 			/* we treat the high watermark as reserved pages. */
 			max += high_wmark_pages(zone);
 
-			if (max > managed_pages)
-				max = managed_pages;
+			max = min_t(unsigned long, max, managed_pages);
 
 			pgdat->totalreserve_pages += max;
 
-- 
2.43.0