Re: [RFC v4 PATCH 2/9] mm/hugetlb: expose hugetlb fault mutex for use by fallocate

From: Mike Kravetz
Date: Wed Jun 17 2015 - 18:06:23 EST

On 06/11/2015 03:46 PM, Davidlohr Bueso wrote:
On Thu, 2015-06-11 at 14:01 -0700, Mike Kravetz wrote:
/* Forward declaration */
static int hugetlb_acct_memory(struct hstate *h, long delta);
@@ -3324,7 +3324,8 @@ static u32 fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
unsigned long key[2];
u32 hash;

- if (vma->vm_flags & VM_SHARED) {
+ /* !vma implies this was called from hugetlbfs fallocate code */
+ if (!vma || vma->vm_flags & VM_SHARED) {

That !vma is icky, and really no need for it: hugetlbfs_fallocate(), for
example, already passes [pseudo]vma->vm_flags with VM_SHARED, and you
say it yourself in the comment. Do you see any reason why we cannot just
keep the vma->vm_flags & VM_SHARED check?

Ah, I did not recall all the users of this code until I went to change
it. The other user is truncate_hugapages() which will now be used for
fallocate hole punch. Truncate like fallocate is an inode operation
and there is no specific vma. I can create a pseudo-vma here as well
just to pass the flag. I guess that would at least be consistent with
the other user.

Mike Kravetz
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at