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

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Date:	Thu, 11 Jun 2015 15:46:06 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Mike Kravetz <mike.kravetz@...cle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC v4 PATCH 2/9] mm/hugetlb: expose hugetlb fault mutex for
 use by fallocate

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?

> +/*
> + * Interface for use by hugetlbfs fallocate code.  Faults must be
> + * synchronized with page adds or deletes by fallocate.  fallocate
> + * only deals with shared mappings.  See also hugetlb_fault_mutex_lock
> + * and hugetlb_fault_mutex_unlock.
> + */
> +u32 hugetlb_fault_mutex_shared_hash(struct address_space *mapping, pgoff_t idx)
> +{
> +	return fault_mutex_hash(NULL, NULL, NULL, mapping, idx, 0);
> +}

It strikes me that this too should be static inlined. But I really
dislike the nil params thing, which should be addressed by my comment
above.

Thanks,
Davidlohr

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