[patch V3 10/20] sched/mmcid: Convert mm CID mask to a bitmap

Thomas Gleixner
2025-10-29T13:09:16Z

This is truly a bitmap and just conveniently uses a cpumask because the
maximum size of the bitmap is nr_cpu_ids.

But that prevents to do searches for a zero bit in a limited range, which
is helpful to provide an efficient mechanism to consolidate the CID space
when the number of users decreases.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
V3: Zero the bitmap with length of bitmap_size(nr_possible_cpus()) - Shrikanth
---
include/linux/mm_types.h | 6 +++---
kernel/sched/core.c | 2 +-
kernel/sched/sched.h | 6 +++---
3 files changed, 7 insertions(+), 7 deletions(-)

--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1342,13 +1342,13 @@ static inline cpumask_t *mm_cpus_allowed
}

/* Accessor for struct mm_struct's cidmask. */
-static inline cpumask_t *mm_cidmask(struct mm_struct *mm)
+static inline unsigned long *mm_cidmask(struct mm_struct *mm)
{
unsigned long cid_bitmap = (unsigned long)mm_cpus_allowed(mm);

/* Skip mm_cpus_allowed */
cid_bitmap += cpumask_size();
- return (struct cpumask *)cid_bitmap;
+ return (unsigned long *)cid_bitmap;
}

static inline void mm_init_cid(struct mm_struct *mm, struct task_struct *p)
@@ -1363,7 +1363,7 @@ static inline void mm_init_cid(struct mm
mm->mm_cid.nr_cpus_allowed = p->nr_cpus_allowed;
raw_spin_lock_init(&mm->mm_cid.lock);
cpumask_copy(mm_cpus_allowed(mm), &p->cpus_mask);
- cpumask_clear(mm_cidmask(mm));
+ bitmap_zero(mm_cidmask(mm), bitmap_size(num_possible_cpus()));
}

static inline int mm_alloc_cid_noprof(struct mm_struct *mm, struct task_struct *p)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10400,7 +10400,7 @@ void sched_mm_cid_exit_signals(struct ta
guard(preempt)();
t->mm_cid.active = 0;
if (t->mm_cid.cid != MM_CID_UNSET) {
- cpumask_clear_cpu(t->mm_cid.cid, mm_cidmask(mm));
+ clear_bit(t->mm_cid.cid, mm_cidmask(mm));
t->mm_cid.cid = MM_CID_UNSET;
}
}
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3558,7 +3558,7 @@ static inline bool __mm_cid_get(struct t

if (cid >= max_cids)
return false;
- if (cpumask_test_and_set_cpu(cid, mm_cidmask(mm)))
+ if (test_and_set_bit(cid, mm_cidmask(mm)))
return false;
t->mm_cid.cid = t->mm_cid.last_cid = cid;
__this_cpu_write(mm->mm_cid.pcpu->cid, cid);
@@ -3581,7 +3581,7 @@ static inline bool mm_cid_get(struct tas
return true;

/* Try the first zero bit in the cidmask. */
- return __mm_cid_get(t, cpumask_first_zero(mm_cidmask(mm)), max_cids);
+ return __mm_cid_get(t, find_first_zero_bit(mm_cidmask(mm), num_possible_cpus()), max_cids);
}

static inline void mm_cid_select(struct task_struct *t)
@@ -3602,7 +3602,7 @@ static inline void switch_mm_cid(struct
{
if (prev->mm_cid.active) {
if (prev->mm_cid.cid != MM_CID_UNSET)
- cpumask_clear_cpu(prev->mm_cid.cid, mm_cidmask(prev->mm));
+ clear_bit(prev->mm_cid.cid, mm_cidmask(prev->mm));
prev->mm_cid.cid = MM_CID_UNSET;
}