linux-kernel - Re: [PATCHv3 1/2] mm: introduce vm_ops->map

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Date:	Tue, 4 Mar 2014 03:26:13 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>, Ning Qu <quning@...il.com>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCHv3 1/2] mm: introduce vm_ops->map_pages()

On Mon, Mar 03, 2014 at 03:16:11PM -0800, Andrew Morton wrote:
> On Thu, 27 Feb 2014 21:53:46 +0200 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
> 
> > The patch introduces new vm_ops callback ->map_pages() and uses it for
> > mapping easy accessible pages around fault address.
> > 
> > On read page fault, if filesystem provides ->map_pages(), we try to map
> > up to FAULT_AROUND_PAGES pages around page fault address in hope to
> > reduce number of minor page faults.
> > 
> > We call ->map_pages first and use ->fault() as fallback if page by the
> > offset is not ready to be mapped (cold page cache or something).
> >
> > ...
> >
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> >
> > ...
> >
> > @@ -571,6 +576,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> >  		pte = pte_mkwrite(pte);
> >  	return pte;
> >  }
> > +
> > +void do_set_pte(struct vm_area_struct *vma, unsigned long address,
> > +		struct page *page, pte_t *pte, bool write, bool anon);
> >  #endif
> >  
> >  /*
> 
> lguest made a dubious naming decision:
> 
> drivers/lguest/page_tables.c:890: error: conflicting types for 'do_set_pte'
> include/linux/mm.h:593: note: previous declaration of 'do_set_pte' was here
> 
> I'll rename lguest's do_set_pte() to do_guest_set_pte() as a
> preparatory patch.

Thanks.

> btw, do_set_pte() could really do with some documentation.  It's not a
> trivial function and it does a lot of stuff.  It's exported to other
> compilation units and we should explain the what, the why and
> particularly the locking preconditions.

Like this?

>From f9be5307ed59ab65645377c1da03eaf4167bfcf2 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Tue, 4 Mar 2014 03:15:43 +0200
Subject: [PATCH] mm: documentaton for do_set_pte()

do_set_pte() now exported to other compilation unit. Let's document
interface.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/memory.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index e2d54e818c5b..6dc622b06915 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3319,7 +3319,21 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address,
 	return ret;
 }
 
-
+/**
+ * do_set_pte - setup new PTE entry for given page and add reverse page mapping.
+ *
+ * @vma: virtual memory area
+ * @address: user virtual address
+ * @page: page to map
+ * @pte: pointer to target page table entry
+ * @write: true, if new entry is writable
+ * @anon: true, if it's anonymous page
+ *
+ * Caller must hold page table lock relevant for @pte.
+ *
+ * Target users are page handler itself and implementations of
+ * vm_ops->map_pages.
+ */
 void do_set_pte(struct vm_area_struct *vma, unsigned long address,
 		struct page *page, pte_t *pte, bool write, bool anon)
 {
-- 
 Kirill A. Shutemov
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