linux-kernel - Re: [PATCH 06/10] mm: Add vmf_insert_pfn

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Date:	Mon, 13 Jul 2015 11:02:35 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 06/10] mm: Add vmf_insert_pfn_pmd()

On Mon, Jul 13, 2015 at 09:23:41AM -0400, Jeff Moyer wrote:
> Matthew Wilcox <matthew.r.wilcox@...el.com> writes:
> 
> > +static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> > +		pmd_t *pmd, unsigned long pfn, pgprot_t prot, bool write)
> > +{
> > +	return VM_FAULT_NOPAGE;
> > +}
> 
> What's the point of the return value?

Good point.  Originally, it paralleled insert_pfn() in mm/memory.c, but it
became apparent that the return code of 0 or -Exxx was useless, and in converting insert_pfn_pmd over to VM_FAULT_ codes, all possible return codes were
going to be VM_FAULT_NOPAGE.  It didn't occur to me to take it one step further and make the function return void.

It doesn't make much difference either way:

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 26d0fc1..5ffdcaa 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -837,7 +837,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	return 0;
 }
 
-static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
+static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 		pmd_t *pmd, unsigned long pfn, pgprot_t prot, bool write)
 {
 	struct mm_struct *mm = vma->vm_mm;
@@ -855,7 +855,6 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 		update_mmu_cache_pmd(vma, addr, pmd);
 	}
 	spin_unlock(ptl);
-	return VM_FAULT_NOPAGE;
 }
 
 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
@@ -877,7 +876,8 @@ int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 		return VM_FAULT_SIGBUS;
 	if (track_pfn_insert(vma, &pgprot, pfn))
 		return VM_FAULT_SIGBUS;
-	return insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
+	insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
+	return VM_FAULT_NOPAGE;
 }
 
 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,


I suppose it's slightly cleaner.  I'll integrate this for the next release.
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