linux-kernel - [PATCH 2/2] devtmpfs: actually reclaim some init memory

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Message-Id: <20210312103027.2701413-2-linux@rasmusvillemoes.dk>
Date:   Fri, 12 Mar 2021 11:30:27 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Christoph Hellwig <hch@....de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] devtmpfs: actually reclaim some init memory

Currently gcc seems to inline devtmpfs_setup() into devtmpfsd(), so
its memory footprint isn't reclaimed as intended. Mark it noinline to
make sure it gets put in .init.text.

While here, setup_done can also be put in .init.data: After complete()
releases the internal spinlock, the completion object is never touched
again by that thread, and the waiting thread doesn't proceed until it
observes ->done while holding that spinlock.

This is now the same pattern as for kthreadd_done in init/main.c:
complete() is done in a __ref function, while the corresponding
wait_for_completion() is in an __init function.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 drivers/base/devtmpfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index aedeb2dc1a18..8be352ab4ddb 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -371,7 +371,7 @@ int __init devtmpfs_mount(void)
 	return err;
 }

-static DECLARE_COMPLETION(setup_done);
+static __initdata DECLARE_COMPLETION(setup_done);

 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 		  struct device *dev)
@@ -405,7 +405,7 @@ static void __noreturn devtmpfs_work_loop(void)
 	}
 }

-static int __init devtmpfs_setup(void *p)
+static noinline int __init devtmpfs_setup(void *p)
 {
 	int err;

-- 
2.29.2