linux-kernel - [PATCH] drivers/base/memory.c: memory subsys init: skip search for missing blocks

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Date:   Fri,  1 Nov 2019 13:10:54 -0500
From:   Scott Cheloha <cheloha@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Hildenbrand <david@...hat.com>
Cc:     nathanl@...ux.ibm.com, ricklind@...ux.vnet.ibm.com,
        Scott Cheloha <cheloha@...ux.vnet.ibm.com>
Subject: [PATCH] drivers/base/memory.c: memory subsys init: skip search for missing blocks

Add a flag to init_memory_block() to  enable/disable searching for a
matching block before creating a device for the block and adding it to
the memory subsystem's bus.

When the memory subsystem is being initialized there is no need to check
if a given block has already been added to its bus.  The bus is new, so the
block in question cannot yet have a corresponding device.

The search for a missing block is O(n) so this saves substantial time at
boot if there are many such blocks to add.

Signed-off-by: Scott Cheloha <cheloha@...ux.vnet.ibm.com>
---
 drivers/base/memory.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 55907c27075b..1160df4a8feb 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -643,17 +643,21 @@ int register_memory(struct memory_block *memory)
 }
 
 static int init_memory_block(struct memory_block **memory,
-			     unsigned long block_id, unsigned long state)
+			     unsigned long block_id, unsigned long state,
+			     bool may_exist)
 {
 	struct memory_block *mem;
 	unsigned long start_pfn;
 	int ret = 0;
 
-	mem = find_memory_block_by_id(block_id);
-	if (mem) {
-		put_device(&mem->dev);
-		return -EEXIST;
+	if (may_exist) {
+		mem = find_memory_block_by_id(block_id);
+		if (mem) {
+			put_device(&mem->dev);
+			return -EEXIST;
+		}
 	}
+
 	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
 	if (!mem)
 		return -ENOMEM;
@@ -684,7 +688,7 @@ static int add_memory_block(unsigned long base_section_nr)
 	if (section_count == 0)
 		return 0;
 	ret = init_memory_block(&mem, base_memory_block_id(base_section_nr),
-				MEM_ONLINE);
+				MEM_ONLINE, false);
 	if (ret)
 		return ret;
 	mem->section_count = section_count;
@@ -720,7 +724,7 @@ int create_memory_block_devices(unsigned long start, unsigned long size)
 
 	mutex_lock(&mem_sysfs_mutex);
 	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
-		ret = init_memory_block(&mem, block_id, MEM_OFFLINE);
+		ret = init_memory_block(&mem, block_id, MEM_OFFLINE, true);
 		if (ret)
 			break;
 		mem->section_count = sections_per_block;
-- 
2.24.0.rc1