linux-kernel - [PATCH v2 4/6] mips: Optimize max

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Message-ID: <20231202111430.18059-5-fancer.lancer@gmail.com>
Date:   Sat,  2 Dec 2023 14:14:21 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Arnd Bergmann <arnd@...db.de>,
        Aleksandar Rikalo <aleksandar.rikalo@...mia.com>,
        Aleksandar Rikalo <arikalo@...il.com>,
        Dragan Mladjenovic <dragan.mladjenovic@...mia.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Baoquan He <bhe@...hat.com>, Chao-ying Fu <cfu@...ecomp.com>,
        Yinglu Yang <yangyinglu@...ngson.cn>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Mike Rapoport <rppt@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Marc Zyngier <maz@...nel.org>, linux-mips@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 4/6] mips: Optimize max_mapnr init procedure

max_mapnr defines the upper boundary of the pages space in the system.
Currently in case if HIGHMEM is available it's calculated based on the
upper high memory PFN limit value. Seeing there is a case when it isn't
fully correct let's optimize out the max_mapnr variable initialization
procedure to cover all the handled in the paging_init() method cases:
1. If CPU has DC-aliases, then high memory is unavailable so the PFNs
upper boundary is determined by max_low_pfn.
2. Otherwise if high memory is available, use highend_pfn value
representing the upper high memory PFNs limit.
3. Otherwise no high memory is available so set max_mapnr with the
low-memory upper limit.

Signed-off-by: Serge Semin <fancer.lancer@...il.com>

---

Since I haven't seen any problem with the denoted misconfiguration on my
setup, the patch isn't marked as fixes, but is supposed to be considered
as an optimization.
---
 arch/mips/mm/init.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index 6e368a4658b5..b2dce07116e8 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -421,9 +421,13 @@ void __init paging_init(void)
 		       " %ldk highmem ignored\n",
 		       (highend_pfn - max_low_pfn) << (PAGE_SHIFT - 10));
 		max_zone_pfns[ZONE_HIGHMEM] = max_low_pfn;
-	}
 
-	max_mapnr = highend_pfn ? highend_pfn : max_low_pfn;
+		max_mapnr = max_low_pfn;
+	} else if (highend_pfn) {
+		max_mapnr = highend_pfn;
+	} else {
+		max_mapnr = max_low_pfn;
+	}
 #else
 	max_mapnr = max_low_pfn;
 #endif
-- 
2.42.1