linux-kernel - Re: [PATCH 2/4] mm: introduce mm_forbids

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Date:	Wed, 22 Oct 2014 15:59:53 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Bob Liu <lliubbo@...il.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jianyu Zhan <nasa4836@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	kvm@...r.kernel.org, linux390@...ibm.com,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH 2/4] mm: introduce mm_forbids_zeropage function

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

On 10/22/2014 01:09 PM, Dominik Dingel wrote:
> Add a new function stub to allow architectures to disable for
> an mm_structthe backing of non-present, anonymous pages with
> read-only empty zero pages.
> 
> Signed-off-by: Dominik Dingel <dingel@...ux.vnet.ibm.com>
> ---
>  include/linux/mm.h | 4 ++++
>  mm/huge_memory.c   | 2 +-
>  mm/memory.c        | 2 +-
>  3 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index cd33ae2..0a2022e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -56,6 +56,10 @@ extern int sysctl_legacy_va_layout;
>  #define __pa_symbol(x)  __pa(RELOC_HIDE((unsigned long)(x), 0))
>  #endif
>  
> +#ifndef mm_forbids_zeropage
> +#define mm_forbids_zeropage(X)  (0)
> +#endif
> +
>  extern unsigned long sysctl_user_reserve_kbytes;
>  extern unsigned long sysctl_admin_reserve_kbytes;
>  
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index de98415..357a381 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -805,7 +805,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  		return VM_FAULT_OOM;
>  	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
>  		return VM_FAULT_OOM;
> -	if (!(flags & FAULT_FLAG_WRITE) &&
> +	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
>  			transparent_hugepage_use_zero_page()) {
>  		spinlock_t *ptl;
>  		pgtable_t pgtable;
> diff --git a/mm/memory.c b/mm/memory.c
> index 64f82aa..f275a9d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2640,7 +2640,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  		return VM_FAULT_SIGBUS;
>  
>  	/* Use the zero-page for reads */
> -	if (!(flags & FAULT_FLAG_WRITE)) {
> +	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) {
>  		entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
>  						vma->vm_page_prot));
>  		page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
> 
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