linux-kernel - [PATCH 2/2] mm/mm_init.c: do not calculate memmap and reserved pages for empty zone

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Message-Id: <20230601063536.26882-2-haifeng.xu@shopee.com>
Date:   Thu,  1 Jun 2023 06:35:36 +0000
From:   Haifeng Xu <haifeng.xu@...pee.com>
To:     rppt@...nel.org
Cc:     mhocko@...nel.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Haifeng Xu <haifeng.xu@...pee.com>
Subject: [PATCH 2/2] mm/mm_init.c: do not calculate memmap and reserved pages for empty zone

For empty zone, it's unnecessary to account for pages used by memmap.
Also, the pages reserved in dma zone can be ignored.

Signed-off-by: Haifeng Xu <haifeng.xu@...pee.com>
---
 mm/mm_init.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 232efac9a929..b82718d596c3 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1543,6 +1543,13 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		size = zone->spanned_pages;
 		freesize = zone->present_pages;
 
+		if (!size) {
+			nr_kernel_pages += 0;
+			nr_all_pages += 0;
+			zone_init_internals(zone, j, nid, 0);
+			continue;
+		}
+
 		/*
 		 * Adjust freesize so that it accounts for how much memory
 		 * is used by this zone for memmap. This affects the watermark
@@ -1579,10 +1586,6 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		 * And all highmem pages will be managed by the buddy system.
 		 */
 		zone_init_internals(zone, j, nid, freesize);
-
-		if (!size)
-			continue;
-
 		setup_usemap(zone);
 		init_currently_empty_zone(zone, zone->zone_start_pfn, size);
 	}
-- 
2.25.1