linux-kernel - Re: [PATCH -mm] mm, pagemap: Fix soft dirty marking for PMD migration entry

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Message-Id: <8fd6b1d8-6dc3-29a8-0377-e4323b74d6af@linux.vnet.ibm.com>
Date:   Tue, 17 Oct 2017 15:17:38 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Hugh Dickins <hughd@...gle.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Daniel Colascione <dancol@...gle.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [PATCH -mm] mm, pagemap: Fix soft dirty marking for PMD migration
 entry

On 10/17/2017 01:48 PM, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.com>
> 
> Now, when the page table is walked in the implementation of
> /proc/<pid>/pagemap, pmd_soft_dirty() is used for both the PMD huge
> page map and the PMD migration entries.  That is wrong,
> pmd_swp_soft_dirty() should be used for the PMD migration entries
> instead because the different page table entry flag is used.

Yeah, different flags can be used on various archs to represent
mapped a PMD and a migration PMD entry. Sounds good.

> 
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: Daniel Colascione <dancol@...gle.com>
> Cc: Zi Yan <zi.yan@...rutgers.edu>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> ---
>  fs/proc/task_mmu.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 2593a0c609d7..01aad772f8db 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1311,13 +1311,15 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
>  		pmd_t pmd = *pmdp;
>  		struct page *page = NULL;
>  
> -		if ((vma->vm_flags & VM_SOFTDIRTY) || pmd_soft_dirty(pmd))
> +		if (vma->vm_flags & VM_SOFTDIRTY)
>  			flags |= PM_SOFT_DIRTY;
>  
>  		if (pmd_present(pmd)) {
>  			page = pmd_page(pmd);
>  
>  			flags |= PM_PRESENT;
> +			if (pmd_soft_dirty(pmd))
> +				flags |= PM_SOFT_DIRTY;
>  			if (pm->show_pfn)
>  				frame = pmd_pfn(pmd) +
>  					((addr & ~PMD_MASK) >> PAGE_SHIFT);
> @@ -1329,6 +1331,8 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
>  			frame = swp_type(entry) |
>  				(swp_offset(entry) << MAX_SWAPFILES_SHIFT);
>  			flags |= PM_SWAP;
> +			if (pmd_swp_soft_dirty(pmd))
> +				flags |= PM_SOFT_DIRTY;

Though I was initially skeptical about whether this will compile
on POWER because of lack of a pmd_swp_soft_dirty() definition
but it turns out we have a generic one to fallback on as we dont
define ARCH_ENABLE_THP_MIGRATION yet.

#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
#ifndef CONFIG_ARCH_ENABLE_THP_MIGRATION
static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
{
	return pmd;
}

static inline int pmd_swp_soft_dirty(pmd_t pmd)
{
	return 0;
}

static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
{
	return pmd;
}
#endif