linux-kernel - Re: [PATCHv5 23/28] thp: add option to setup migration entiries during PMD split

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Date:	Tue, 19 May 2015 15:55:12 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 23/28] thp: add option to setup migration entiries during
 PMD split

On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> We are going to use migration PTE entires to stabilize page counts.
> If the page is mapped with PMDs we need to split the PMD and setup
> migration enties. It's reasonable to combine these operations to avoid
> double-scanning over the page table.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>   mm/huge_memory.c | 23 +++++++++++++++--------
>   1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 5885ef8f0fad..2f9e2e882bab 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -23,6 +23,7 @@
>   #include <linux/pagemap.h>
>   #include <linux/migrate.h>
>   #include <linux/hashtable.h>
> +#include <linux/swapops.h>
>
>   #include <asm/tlb.h>
>   #include <asm/pgalloc.h>
> @@ -2551,7 +2552,7 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
>   }
>
>   static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> -		unsigned long haddr)
> +		unsigned long haddr, bool freeze)
>   {
>   	struct mm_struct *mm = vma->vm_mm;
>   	struct page *page;
> @@ -2593,12 +2594,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>   		 * transferred to avoid any possibility of altering
>   		 * permissions across VMAs.
>   		 */
> -		entry = mk_pte(page + i, vma->vm_page_prot);
> -		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> -		if (!write)
> -			entry = pte_wrprotect(entry);
> -		if (!young)
> -			entry = pte_mkold(entry);
> +		if (freeze) {
> +			swp_entry_t swp_entry;
> +			swp_entry = make_migration_entry(page + i, write);
> +			entry = swp_entry_to_pte(swp_entry);
> +		} else {
> +			entry = mk_pte(page + i, vma->vm_page_prot);
> +			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
> +			if (!write)
> +				entry = pte_wrprotect(entry);
> +			if (!young)
> +				entry = pte_mkold(entry);
> +		}
>   		pte = pte_offset_map(&_pmd, haddr);
>   		BUG_ON(!pte_none(*pte));
>   		set_pte_at(mm, haddr, pte, entry);
> @@ -2625,7 +2632,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>   	mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
>   	ptl = pmd_lock(mm, pmd);
>   	if (likely(pmd_trans_huge(*pmd)))
> -		__split_huge_pmd_locked(vma, pmd, haddr);
> +		__split_huge_pmd_locked(vma, pmd, haddr, false);
>   	spin_unlock(ptl);
>   	mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
>   }
>

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