linux-kernel - [PATCH 1/4] proc/kcore: mark proc entry as permanent

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Message-ID: <60873e6afcfda3f08d0456f19e4733612afcf134.1731115587.git.osandov@fb.com>
Date: Fri,  8 Nov 2024 17:28:39 -0800
From: Omar Sandoval <osandov@...ndov.com>
To: linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Cc: kernel-team@...com,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] proc/kcore: mark proc entry as permanent

From: Omar Sandoval <osandov@...com>

drgn reads from /proc/kcore to debug the running kernel. For many drgn
scripts, /proc/kcore is actually a bottleneck.

use_pde() and unuse_pde() in prog_reg_read() show up hot in profiles.
Since the entry for /proc/kcore can never be removed, this is useless
overhead that can be trivially avoided by marking the entry as
permanent.

In my benchmark, this reduces the time per read by about 20 nanoseconds,
from 235 nanoseconds per read to 215.

Link: https://github.com/osandov/drgn/issues/106
Signed-off-by: Omar Sandoval <osandov@...com>
---
 fs/proc/kcore.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 51446c59388f..770e4e57f445 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -662,6 +662,7 @@ static int release_kcore(struct inode *inode, struct file *file)
 }

 static const struct proc_ops kcore_proc_ops = {
+	.proc_flags	= PROC_ENTRY_PERMANENT,
 	.proc_read_iter	= read_kcore_iter,
 	.proc_open	= open_kcore,
 	.proc_release	= release_kcore,
-- 
2.47.0