linux-kernel - [PATCH] proc: spread likely/unlikely a bit

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Date:   Thu, 4 Jan 2018 20:56:57 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] proc: spread likely/unlikely a bit

use_pde() is used at every open/read/write/... of every random /proc
file. Negative refcount happens only if PDE is being deleted by module
(read: never). So it gets "likely".

unuse_pde() gets "unlikely" for the same reason.

close_pdeo() gets unlikely as the completion is filled only if there is
a race between PDE removal and close() (read: never ever).

It even saves code on x86_64 defconfig:

	add/remove: 0/0 grow/shrink: 1/2 up/down: 2/-20 (-18)
	Function                                     old     new   delta
	close_pdeo                                   183     185      +2
	proc_reg_get_unmapped_area                   119     111      -8
	proc_reg_poll                                 85      73     -12

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/inode.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -129,12 +129,12 @@ enum {BIAS = -1U<<31};
 
 static inline int use_pde(struct proc_dir_entry *pde)
 {
-	return atomic_inc_unless_negative(&pde->in_use);
+	return likely(atomic_inc_unless_negative(&pde->in_use));
 }
 
 static void unuse_pde(struct proc_dir_entry *pde)
 {
-	if (atomic_dec_return(&pde->in_use) == BIAS)
+	if (unlikely(atomic_dec_return(&pde->in_use) == BIAS))
 		complete(pde->pde_unload_completion);
 }
 
@@ -167,7 +167,7 @@ static void close_pdeo(struct proc_dir_entry *pde, struct pde_opener *pdeo)
 		spin_lock(&pde->pde_unload_lock);
 		/* After ->release. */
 		list_del(&pdeo->lh);
-		if (pdeo->c)
+		if (unlikely(pdeo->c))
 			complete(pdeo->c);
 		kfree(pdeo);
 	}
@@ -421,7 +421,7 @@ static const char *proc_get_link(struct dentry *dentry,
 				 struct delayed_call *done)
 {
 	struct proc_dir_entry *pde = PDE(inode);
-	if (unlikely(!use_pde(pde)))
+	if (!use_pde(pde))
 		return ERR_PTR(-EINVAL);
 	set_delayed_call(done, proc_put_link, pde);
 	return pde->data;