linux-kernel - [PATCH] fs/proc: Move kfree outside pde_unload

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Message-Id: <1345653510-22000-1-git-send-email-nzimmer@sgi.com>
Date:	Wed, 22 Aug 2012 11:38:29 -0500
From:	Nathan Zimmer <nzimmer@....com>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	adobriyan@...il.com, Nathan Zimmer <nzimmer@....com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	David Woodhouse <dwmw2@...radead.org>
Subject: [PATCH] fs/proc: Move kfree outside pde_unload_lock

This moves a kfree outside a spinlock to help scaling on larger (512 core)
systems.

I ran a simple test which just reads from /proc/cpuinfo.
Lower is better, as you can see the worst case scenario is improved.

	baseline	moved kfree
tasks	read-sec	read-sec
1	0.0141		0.0141
2	0.0140		0.0140
4	0.0140		0.0141
8	0.0145		0.0145
16	0.0553		0.0548
32	0.1688		0.1622
64	0.5017		0.3856
128	1.7005		0.9710
256	5.2513		2.6519
512	8.0529		6.2976

Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: David Woodhouse <dwmw2@...radead.org>
Acked-by: Alexey Dobriyan <adobriyan@...il.com>
Signed-off-by: Nathan Zimmer <nzimmer@....com>
---
 fs/proc/inode.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 7ac817b..bf36266 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -403,9 +403,9 @@ static int proc_reg_release(struct inode *inode, struct file *file)
 	release = pde->proc_fops->release;
 	if (pdeo) {
 		list_del(&pdeo->lh);
-		kfree(pdeo);
 	}
 	spin_unlock(&pde->pde_unload_lock);
+	kfree(pdeo);
 
 	if (release)
 		rv = release(inode, file);
-- 
1.6.0.2

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