Hey Yafang,
On 2025/9/10 10:44, Yafang Shao wrote:
Since a task with MMF_DISABLE_THP_COMPLETELY cannot use THP, remove it from
the khugepaged_mm_slot to stop khugepaged from processing it.
After this change, the following semantic relationship always holds:
MMF_VM_HUGEPAGE is set == task is in khugepaged mm_slot
MMF_VM_HUGEPAGE is not set == task is not in khugepaged mm_slot
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
---
include/linux/khugepaged.h | 1 +
kernel/sys.c | 6 ++++++
mm/khugepaged.c | 19 +++++++++----------
3 files changed, 16 insertions(+), 10 deletions(-)
diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index eb1946a70cff..6cb9107f1006 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -19,6 +19,7 @@ extern void khugepaged_min_free_kbytes_update(void);
extern bool current_is_khugepaged(void);
extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
bool install_pmd);
+bool hugepage_pmd_enabled(void);
static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
diff --git a/kernel/sys.c b/kernel/sys.c
index a46d9b75880b..a1c1e8007f2d 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -8,6 +8,7 @@
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/mm_inline.h>
+#include <linux/khugepaged.h>
#include <linux/utsname.h>
#include <linux/mman.h>
#include <linux/reboot.h>
@@ -2493,6 +2494,11 @@ static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
mm_flags_clear(MMF_DISABLE_THP_COMPLETELY, mm);
mm_flags_clear(MMF_DISABLE_THP_EXCEPT_ADVISED, mm);
}
+
+ if (!mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) &&
+ !mm_flags_test(MMF_VM_HUGEPAGE, mm) &&
+ hugepage_pmd_enabled())
+ __khugepaged_enter(mm);
mmap_write_unlock(current->mm);
One minor style suggestion for prctl_set_thp_disable():
static int prctl_set_thp_disable(bool thp_disable, unsigned long flags,
unsigned long arg4, unsigned long arg5)
{
struct mm_struct *mm = current->mm;
[...]
if (mmap_write_lock_killable(current->mm))
return -EINTR;
[...]
mmap_write_unlock(current->mm);
return 0;
}
It initializes struct mm_struct *mm = current->mm; at the beginning, but
then uses both mm and current->mm. Could you change the calls using
current->mm to use the local mm variable for consistency? Just a nit ;)
Cheers,
Lance
return 0;
}
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4ec324a4c1fe..88ac482fb3a0 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -413,7 +413,7 @@ static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm)
mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm);
}
-static bool hugepage_pmd_enabled(void)
+bool hugepage_pmd_enabled(void)
{
/*
* We cover the anon, shmem and the file-backed case here; file-backed
@@ -445,6 +445,7 @@ void __khugepaged_enter(struct mm_struct *mm)
/* __khugepaged_exit() must not run from under us */
VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
+ WARN_ON_ONCE(mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm));
if (unlikely(mm_flags_test_and_set(MMF_VM_HUGEPAGE, mm)))
return;
@@ -472,7 +473,8 @@ void __khugepaged_enter(struct mm_struct *mm)
void khugepaged_enter_vma(struct vm_area_struct *vma,
vm_flags_t vm_flags)
{
- if (!mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
+ if (!mm_flags_test(MMF_DISABLE_THP_COMPLETELY, vma->vm_mm) &&
+ !mm_flags_test(MMF_VM_HUGEPAGE, vma->vm_mm) &&
hugepage_pmd_enabled()) {
if (thp_vma_allowable_order(vma, vm_flags, TVA_KHUGEPAGED, PMD_ORDER))
__khugepaged_enter(vma->vm_mm);
@@ -1451,16 +1453,13 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
lockdep_assert_held(&khugepaged_mm_lock);
- if (hpage_collapse_test_exit(mm)) {
+ if (hpage_collapse_test_exit_or_disable(mm)) {
/* free mm_slot */
hash_del(&slot->hash);
list_del(&slot->mm_node);
- /*
- * Not strictly needed because the mm exited already.
- *
- * mm_flags_clear(MMF_VM_HUGEPAGE, mm);
- */
+ /* If the mm is disabled, this flag must be cleared. */
+ mm_flags_clear(MMF_VM_HUGEPAGE, mm);
/* khugepaged_mm_lock actually not necessary for the below */
mm_slot_free(mm_slot_cache, mm_slot);
@@ -2507,9 +2506,9 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
/*
* Release the current mm_slot if this mm is about to die, or
- * if we scanned all vmas of this mm.
+ * if we scanned all vmas of this mm, or if this mm is disabled.
*/
- if (hpage_collapse_test_exit(mm) || !vma) {
+ if (hpage_collapse_test_exit_or_disable(mm) || !vma) {
/*
* Make sure that if mm_users is reaching zero while
* khugepaged runs here, khugepaged_exit will find
