linux-kernel - Re: [PATCHv2 3/3] mm: Use updated pmdp_invalidate() inteface to track dirty/accessed bits

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Date:   Fri, 16 Jun 2017 21:27:04 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 3/3] mm: Use updated pmdp_invalidate() inteface to track
 dirty/accessed bits



On Friday 16 June 2017 06:51 PM, Kirill A. Shutemov wrote:
> On Fri, Jun 16, 2017 at 05:01:30PM +0530, Aneesh Kumar K.V wrote:
>> "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> writes:
>>
>>> This patch uses modifed pmdp_invalidate(), that return previous value of pmd,
>>> to transfer dirty and accessed bits.
>>>
>>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>> ---
>>>   fs/proc/task_mmu.c |  8 ++++----
>>>   mm/huge_memory.c   | 29 ++++++++++++-----------------
>>>   2 files changed, 16 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>> index f0c8b33d99b1..f2fc1ef5bba2 100644
>>> --- a/fs/proc/task_mmu.c
>>> +++ b/fs/proc/task_mmu.c
>>
>> .....
>>
>>> @@ -1965,7 +1955,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>>   	page_ref_add(page, HPAGE_PMD_NR - 1);
>>>   	write = pmd_write(*pmd);
>>>   	young = pmd_young(*pmd);
>>> -	dirty = pmd_dirty(*pmd);
>>>   	soft_dirty = pmd_soft_dirty(*pmd);
>>>
>>>   	pmdp_huge_split_prepare(vma, haddr, pmd);
>>> @@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>>   			if (soft_dirty)
>>>   				entry = pte_mksoft_dirty(entry);
>>>   		}
>>> -		if (dirty)
>>> -			SetPageDirty(page + i);
>>>   		pte = pte_offset_map(&_pmd, addr);
>>>   		BUG_ON(!pte_none(*pte));
>>>   		set_pte_at(mm, addr, pte, entry);
>>> @@ -2045,7 +2032,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>>   	 * and finally we write the non-huge version of the pmd entry with
>>>   	 * pmd_populate.
>>>   	 */
>>> -	pmdp_invalidate(vma, haddr, pmd);
>>> +	old = pmdp_invalidate(vma, haddr, pmd);
>>> +
>>> +	/*
>>> +	 * Transfer dirty bit using value returned by pmd_invalidate() to be
>>> +	 * sure we don't race with CPU that can set the bit under us.
>>> +	 */
>>> +	if (pmd_dirty(old))
>>> +		SetPageDirty(page);
>>> +
>>>   	pmd_populate(mm, pmd, pgtable);
>>>
>>>   	if (freeze) {
>>
>>
>> Can we invalidate the pmd early here ? ie, do pmdp_invalidate instead of
>> pmdp_huge_split_prepare() ?
> 
> I think we can. But it means we would block access to the page for longer
> than it's necessary on most architectures. I guess it's not a bit deal.
> 
> Maybe as separate patch on top of this patchet? Aneesh, would you take
> care of this?
> 

Yes, I cam do that.

-aneesh