proc/kcore: mark proc entry as permanent

osandov · brauner · commit c9136fad4c08 · 2024-12-02T11:21:03.000+01:00
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: osandov/drgn#106 Signed-off-by: Omar Sandoval <osandov@fb.com> Link: https://lore.kernel.org/r/60873e6afcfda3f08d0456f19e4733612afcf134.1731115587.git.osandov@fb.com Signed-off-by: Christian Brauner <brauner@kernel.org>
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
@@ -663,6 +663,7 @@ 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,

Original file line number	Diff line number	Diff line change
`@@ -663,6 +663,7 @@ static int release_kcore(struct inode inode, struct file file)`
`663`	`663`	`}`
`664`	`664`
`665`	`665`	`static const struct proc_ops kcore_proc_ops = {`
	`666`	`+ .proc_flags = PROC_ENTRY_PERMANENT,`
`666`	`667`	`.proc_read_iter = read_kcore_iter,`
`667`	`668`	`.proc_open = open_kcore,`
`668`	`669`	`.proc_release = release_kcore,`