linux-kernel - [PATCH 9/9] mm: vmalloc: Scale and activate cvz

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Date:   Mon, 22 May 2023 13:08:49 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: [PATCH 9/9] mm: vmalloc: Scale and activate cvz_size

Scale a zone size to number of CPUs. Each power of two
value adds extra 100 * PAGE_SIZE bytes to a zone size.

A maximum zone size limit is set to 4M, it is reached
if number of CPUs=1024 and PAGE_SIZE=4096 bytes.

For 32-bit or single core systems cvz_size is set to
ULONG_MAX. It means that a pre-loading technique is
deactivated.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 mm/vmalloc.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 8054b8bf6c18..a5e6956a8da4 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -806,8 +806,6 @@ struct cpu_vmap_zone {
 };
 
 static DEFINE_PER_CPU(struct cpu_vmap_zone, cpu_vmap_zone);
-
-/* Disable a per-cpu caching. */
 static __read_mostly unsigned long cvz_size = ULONG_MAX;
 
 static inline unsigned int
@@ -4490,6 +4488,19 @@ static void vmap_init_pcpu_zones(void)
 			spin_lock_init(&z->fbl[j].lock);
 		}
 	}
+
+	/*
+	 * Scale a zone size to number of CPUs. Each power of two
+	 * value adds extra 100 pages to a zone size. A high-threshold
+	 * limit is set to 4M. It can be reached if number of CPUs=1024
+	 * whereas a PAGE_SIZE is 4096 bytes.
+	 */
+#if BITS_PER_LONG == 64
+	if (i > 1) {
+		cvz_size = fls(i) * (100 * PAGE_SIZE);
+		cvz_size = min(cvz_size, (unsigned long) SZ_4M);
+	}
+#endif
 }
 
 void __init vmalloc_init(void)
-- 
2.30.2