[PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[Dipendra Khadka]

The 'h' length modifier in '%hd' is unnecessary as short integers are
promoted to int in variadic functions. Use '%d' instead.

Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>
---
 mm/oom_kill.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5eb11fbba704..94066316e3ec 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -458,7 +458,7 @@ static void dump_oom_victim(struct oom_control *oc, struct task_struct *victim)
 
 static void dump_header(struct oom_control *oc)
 {
-	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
+	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%d\n",
 		current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
 			current->signal->oom_score_adj);
 	if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
@@ -958,7 +958,7 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 	 */
 	do_send_sig_info(SIGKILL, SEND_SIG_PRIV, victim, PIDTYPE_TGID);
 	mark_oom_victim(victim);
-	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
+	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%d\n",
 		message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
 		K(get_mm_counter(mm, MM_ANONPAGES)),
 		K(get_mm_counter(mm, MM_FILEPAGES)),
-- 
2.43.0

Re: [PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[David Rientjes]

On Sun, 28 Dec 2025, Dipendra Khadka wrote:

> The 'h' length modifier in '%hd' is unnecessary as short integers are
> promoted to int in variadic functions. Use '%d' instead.
> 
> Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>

I don't have a strong opinion given this will result in the same output.

Acked-by: David Rientjes <rientjes@google.com>

Re: [PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[Michal Hocko]

On Sun 28-12-25 15:44:55, Dipendra Khadka wrote:
> The 'h' length modifier in '%hd' is unnecessary as short integers are
> promoted to int in variadic functions. Use '%d' instead.
> 
> Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>

Why should we change the currently correct code in the first place?
What is an added value?

-- 
Michal Hocko
SUSE Labs

Re: [PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[Andrew Morton]

On Mon, 29 Dec 2025 09:27:18 +0100 Michal Hocko <mhocko@suse.com> wrote:

> On Sun 28-12-25 15:44:55, Dipendra Khadka wrote:
> > The 'h' length modifier in '%hd' is unnecessary as short integers are
> > promoted to int in variadic functions. Use '%d' instead.
> > 
> > Signed-off-by: Dipendra Khadka <kdipendra88@gmail.com>
> 
> Why should we change the currently correct code in the first place?
> What is an added value?

It reduces vmlinux by 2 bytes ;)

It's a teeny issue but I do like the present code - be very explicit
and careful about the types we're dealing with, don't rely on unobvious
C rules.

Re: [PATCH] mm/oom_kill: Remove unnecessary integer promotion in format string

[Dipendra Khadka]

>It's a teeny issue but I do like the present code - be very explicit
>and careful about the types we're dealing with, don't rely on unobvious
>C rules.

Actually, the scenario here is that while printing a short, it is 
**promoted** to int due to C's variadic argument promotion rules.

Yes, we must use %hd when the **semantic type** is short. However, 
due to integer promotion, the value is already passed as a 4-byte int 
on the stack. The %hd format specifier then casts it back to short 
for display.

Since the value is already promoted to int internally, using %d is 
simpler and avoids the unnecessary cast. The checkpatch warning 
confirms this:

```
WARNING: Integer promotion: Using 'h' in '%hd' is unnecessary
#461: FILE: mm/oom_kill.c:461:
+	pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), order=%d, oom_score_adj=%hd\n",
+		current->comm, oc->gfp_mask, &oc->gfp_mask, oc->order,
+			current->signal->oom_score_adj);


WARNING: Integer promotion: Using 'h' in '%hd' is unnecessary
#961: FILE: mm/oom_kill.c:961:
+	pr_err("%s: Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB, UID:%u pgtables:%lukB oom_score_adj:%hd\n",
+		message, task_pid_nr(victim), victim->comm, K(mm->total_vm),
+		K(get_mm_counter(mm, MM_ANONPAGES)),
+		K(get_mm_counter(mm, MM_FILEPAGES)),
+		K(get_mm_counter(mm, MM_SHMEMPAGES)),
+		from_kuid(&init_user_ns, task_uid(victim)),
+		mm_pgtables_bytes(mm) >> 10, victim->signal->oom_score_adj);
```

Checkpatch flags the 'h' modifier as unnecessary for this reason, 
and many other subsystems have moved to using %d for promoted types. 
Hence, I think this patch aligns with kernel coding practices.

Best Rgards,
Dipendra Khadka