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Subject[PATCH -mm] proc: faster open/close of files without ->release hook
The whole point of code in fs/proc/inode.c is to make sure ->release
hook is called either at close() or at rmmod time.

All if it is unnecessary if there is no ->release hook.

Save allocation+list manipulations under spinlock in that case.

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

fs/proc/inode.c | 41 +++++++++++++++++++++++------------------
1 file changed, 23 insertions(+), 18 deletions(-)

--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -342,31 +342,36 @@ static int proc_reg_open(struct inode *inode, struct file *file)
*
* Save every "struct file" with custom ->release hook.
*/
- pdeo = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);
- if (!pdeo)
- return -ENOMEM;
-
- if (!use_pde(pde)) {
- kfree(pdeo);
+ if (!use_pde(pde))
return -ENOENT;
- }
- open = pde->proc_fops->open;
+
release = pde->proc_fops->release;
+ if (release) {
+ pdeo = kmalloc(sizeof(struct pde_opener), GFP_KERNEL);
+ if (!pdeo) {
+ rv = -ENOMEM;
+ goto out_unuse;
+ }
+ }

+ open = pde->proc_fops->open;
if (open)
rv = open(inode, file);

- if (rv == 0 && release) {
- /* To know what to release. */
- pdeo->file = file;
- pdeo->closing = false;
- pdeo->c = NULL;
- spin_lock(&pde->pde_unload_lock);
- list_add(&pdeo->lh, &pde->pde_openers);
- spin_unlock(&pde->pde_unload_lock);
- } else
- kfree(pdeo);
+ if (release) {
+ if (rv == 0) {
+ /* To know what to release. */
+ pdeo->file = file;
+ pdeo->closing = false;
+ pdeo->c = NULL;
+ spin_lock(&pde->pde_unload_lock);
+ list_add(&pdeo->lh, &pde->pde_openers);
+ spin_unlock(&pde->pde_unload_lock);
+ } else
+ kfree(pdeo);
+ }

+out_unuse:
unuse_pde(pde);
return rv;
}
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