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mm->def_flags cleanups (Was: Change khugepaged to respect MMF_THP_DISABLE flag)

Oleg Nesterov lkml 1 version In review

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  1. v1 Latest2 patches 9 repliesIn review

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#Subject and filesSizeRepliesApplied
1/2exec: kill the unnecessary mm->def_flags setting in load_elf_binary()fs/binfmt_elf.c+0 -40 replies
2/2mm: thp: kill the bogus ->def_flags check in hugepage_madvise()mm/huge_memory.c+0 -23 replies

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Cover letter [PATCH 0/2] mm->def_flags cleanups (Was: Change khugepaged to respect MMF_THP_DISABLE flag)

Alex, Andrew, I think this simple series makes sense in any case, but _perhaps_ it can also help THP_DISABLE.

Quoted 7 lines · Alex Thorlton
Quoted 4 lines · Oleg Nesterov

Although I got lost a bit, and probably misunderstood... but it seems to me that whatever you do this patch should not touch khugepaged_scan_mm_slot.

Quoted 5 lines

Maybe I've gotten myself confused as well :) After looking through the code some more, my understanding is that khugepaged_test_exit is used to make sure that __khugepaged_exit isn't running from underneath at certain times, so to have khugepaged_test_exit return true when __khugepaged_exit is not necessarily running, seems incorrect to me.

Still can't understand... probably I need to see v3.

But you know, I have another idea. Not sure you will like it, and probably I missed something.

Can't we simply add VM_NOHUGEPAGE into ->def_flags? See the (untested) patch below, on top of this series.

What do you think?

Oleg.

include/linux/mm.h +2 -0
index 1cedd00..bc1dd9e 100644
@@ -167,6 +167,8 @@ extern unsigned int kobjsize(const void *objp);
  */
 #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP)
 
+#define VM_INIT_DEF_MASK	VM_NOHUGEPAGE
+
 /*
  * mapping from the currently active vm_flags protection bits (the
  * low four bits) to a page protection mask..
include/uapi/linux/prctl.h +3 -0
index 289760f..58afc04 100644
@@ -149,4 +149,7 @@
 
 #define PR_GET_TID_ADDRESS	40
 
+#define PR_SET_THP_DISABLE	41
+#define PR_GET_THP_DISABLE	42
+
 #endif /* _LINUX_PRCTL_H */
kernel/fork.c +8 -3
index b84bef7..f6d020b 100644
@@ -529,8 +529,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 	atomic_set(&mm->mm_count, 1);
 	init_rwsem(&mm->mmap_sem);
 	INIT_LIST_HEAD(&mm->mmlist);
-	mm->flags = (current->mm) ?
-		(current->mm->flags & MMF_INIT_MASK) : default_dump_filter;
 	mm->core_state = NULL;
 	atomic_long_set(&mm->nr_ptes, 0);
 	memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));

@@ -538,8 +536,15 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 	mm_init_aio(mm);
 	mm_init_owner(mm, p);
 
-	if (likely(!mm_alloc_pgd(mm))) {
+	if (current->mm) {
+		mm->flags = current->mm->flags & MMF_INIT_MASK;
+		mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
+	} else {
+		mm->flags = default_dump_filter;
 		mm->def_flags = 0;
+	}
+
+	if (likely(!mm_alloc_pgd(mm))) {
 		mmu_notifier_mm_init(mm);
 		return mm;
 	}
kernel/sys.c +13 -0
index ac1842e..eb8b0fc 100644
@@ -2029,6 +2029,19 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		if (arg2 || arg3 || arg4 || arg5)
 			return -EINVAL;
 		return current->no_new_privs ? 1 : 0;
+	case PR_SET_THP_DISABLE:
+	case PR_GET_THP_DISABLE:
+		down_write(&me->mm->mmap_sem);
+		if (option == PR_SET_THP_DISABLE) {
+			if (arg2)
+				me->mm->def_flags |= VM_NOHUGEPAGE;
+			else
+				me->mm->def_flags &= ~VM_NOHUGEPAGE;
+		} else {
+			error = !!(me->mm->flags && VM_NOHUGEPAGE);
+		}
+		up_write(&me->mm->mmap_sem);
+		break;
 	default:
 		error = -EINVAL;
 		break;

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