linux-kernel - [PATCH 3/4] workqueue: add a BUILD_BUG_ON() to check the size of struct pool

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Date:   Mon,  1 Jun 2020 08:44:41 +0000
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH 3/4] workqueue: add a BUILD_BUG_ON() to check the size of struct pool_workqueue

Currently, the size of struct pool_workqueue is smaller than the
smellest requirement (1 << WORK_STRUCT_FLAG_BITS). When the size
of struct pool_workqueue is increasing in future development and
exceed the smellest requirement a little, it will be a big waste
due to alignment.

Add a check in case we don't skimp enough in future.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 35120b909234..1921c982f920 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5907,6 +5907,14 @@ void __init workqueue_init_early(void)
 
 	BUILD_BUG_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
 
+	/*
+	 * If it complains when being built, there might be considerable
+	 * memory waste in struct pool_workqueue. Whatever the reason is,
+	 * an updated check here or a re-arrangement in
+	 * struct pool_workqueue is required.
+	 */
+	BUILD_BUG_ON(sizeof(struct pool_workqueue) > (1 << WORK_STRUCT_FLAG_BITS));
+
 	BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
 	cpumask_copy(wq_unbound_cpumask, housekeeping_cpumask(hk_flags));
 
-- 
2.20.1