linux-kernel - Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV

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Date:   Fri, 3 Mar 2017 13:26:36 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Hillf Danton <hillf.zj@...baba-inc.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:     'Andrea Arcangeli' <aarcange@...hat.com>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        'Minchan Kim' <minchan@...nel.org>
Subject: Re: [PATCH 3/4] thp: fix MADV_DONTNEED vs. MADV_FREE race

On Fri, Mar 03, 2017 at 01:35:11PM +0800, Hillf Danton wrote:
> 
> On March 02, 2017 11:11 PM Kirill A. Shutemov wrote: 
> > 
> > Basically the same race as with numa balancing in change_huge_pmd(), but
> > a bit simpler to mitigate: we don't need to preserve dirty/young flags
> > here due to MADV_FREE functionality.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Cc: Minchan Kim <minchan@...nel.org>
> > ---
> >  mm/huge_memory.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index bb2b3646bd78..324217c31ec9 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -1566,8 +1566,6 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> >  		deactivate_page(page);
> > 
> >  	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
> > -		orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
> > -			tlb->fullmm);
> >  		orig_pmd = pmd_mkold(orig_pmd);
> >  		orig_pmd = pmd_mkclean(orig_pmd);
> > 
> $ grep -n set_pmd_at  linux-4.10/arch/powerpc/mm/pgtable-book3s64.c
> 
> /*
>  * set a new huge pmd. We should not be called for updating
>  * an existing pmd entry. That should go via pmd_hugepage_update.
>  */
> void set_pmd_at(struct mm_struct *mm, unsigned long addr,

+Aneesh.

Urgh... Power is special again.

I think this should work fine.

>From 056914fa025992c0a2212aee057c26307ce60238 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Thu, 2 Mar 2017 16:47:45 +0300
Subject: [PATCH] thp: fix MADV_DONTNEED vs. MADV_FREE race

Basically the same race as with numa balancing in change_huge_pmd(), but
a bit simpler to mitigate: we don't need to preserve dirty/young flags
here due to MADV_FREE functionality.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Minchan Kim <minchan@...nel.org>
---
 mm/huge_memory.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bb2b3646bd78..23c1b3d58cf4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1566,8 +1566,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		deactivate_page(page);
 
 	if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
-		orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
-			tlb->fullmm);
+		pmdp_invalidate(vma, addr, pmd);
 		orig_pmd = pmd_mkold(orig_pmd);
 		orig_pmd = pmd_mkclean(orig_pmd);
 
-- 
 Kirill A. Shutemov