linux-kernel - Re: [PATCH 2/4] mm: rename __mlock_vma_pages_range() to populate_vma_page

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Message-ID: <alpine.DEB.2.10.1502121358150.30164@chino.kir.corp.google.com>
Date:	Thu, 12 Feb 2015 13:59:22 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/4] mm: rename __mlock_vma_pages_range() to
 populate_vma_page_range()

On Thu, 12 Feb 2015, Kirill A. Shutemov wrote:

> > I think it makes sense to drop the references about "downgrading" 
> > mm->mmap_sem in the documentation since populate_vma_page_range() can be 
> > called with it held either for read or write depending on the context.
> 
> I'm not sure what references you're talking about.
> 
> Is it about this part:
> 
>  * If @nonblocking is non-NULL, it must held for read only and may be
>  * released.  If it's released, *@...blocking will be set to 0.
> 
> ?
> 

No, I was agreeing with your removal from the documentation:

@@ -463,21 +463,11 @@ populate the page table.
 
 To mlock a range of memory under the unevictable/mlock infrastructure, the
 mmap() handler and task address space expansion functions call
-mlock_vma_pages_range() specifying the vma and the address range to mlock.
-mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in
-"Filtering Special VMAs".  It will clear the VM_LOCKED flag, which will have
-already been set by the caller, in filtered VMAs.  Thus these VMA's need not be
-visited for munlock when the region is unmapped.
-
-For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
-fault/allocate the pages and mlock them.  Again, like mlock_fixup(),
-mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
-attempting to fault/allocate and mlock the pages and "upgrades" the semaphore
-back to write mode before returning.
-
-The callers of mlock_vma_pages_range() will have already added the memory range
+populate_vma_page_range() specifying the vma and the address range to mlock.
+
+The callers of populate_vma_page_range() will have already added the memory range
 to be mlocked to the task's "locked_vm".  To account for filtered VMAs,
-mlock_vma_pages_range() returns the number of pages NOT mlocked.  All of the
+populate_vma_page_range() returns the number of pages NOT mlocked.  All of the
 callers then subtract a non-negative return value from the task's locked_vm.  A
 negative return value represent an error - for example, from get_user_pages()
 attempting to fault in a VMA with PROT_NONE access.  In this case, we leave the
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