linux-kernel - Re: [RFC PATCH 1/2] mm/hugetlbfs: Attempt PUD_SIZE mapping alignment if PMD sharing enabled

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Date:	Thu, 31 Mar 2016 09:45:15 -0700
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, Hugh Dickins <hughd@...gle.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Steve Capper <steve.capper@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 1/2] mm/hugetlbfs: Attempt PUD_SIZE mapping alignment
 if PMD sharing enabled

On 03/30/2016 07:18 PM, Naoya Horiguchi wrote:
> On Mon, Mar 28, 2016 at 06:12:49PM -0700, Mike Kravetz wrote:
>> When creating a hugetlb mapping, attempt PUD_SIZE alignment if the
>> following conditions are met:
>> - Address passed to mmap or shmat is NULL
>> - The mapping is flaged as shared
>> - The mapping is at least PUD_SIZE in length
>> If a PUD_SIZE aligned mapping can not be created, then fall back to a
>> huge page size mapping.
> 
> It would be kinder if the patch description includes why this change.
> Simply "to facilitate pmd sharing" is helpful for someone who read
> "git log".

Ok, will do.

> 
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
>> ---
>>  fs/hugetlbfs/inode.c | 29 +++++++++++++++++++++++++++--
>>  1 file changed, 27 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 540ddc9..22b2e38 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -175,6 +175,17 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>>  	struct vm_area_struct *vma;
>>  	struct hstate *h = hstate_file(file);
>>  	struct vm_unmapped_area_info info;
>> +	bool pud_size_align = false;
>> +	unsigned long ret_addr;
>> +
>> +	/*
>> +	 * If PMD sharing is enabled, align to PUD_SIZE to facilitate
>> +	 * sharing.  Only attempt alignment if no address was passed in,
>> +	 * flags indicate sharing and size is big enough.
>> +	 */
>> +	if (IS_ENABLED(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) &&
>> +	    !addr && flags & MAP_SHARED && len >= PUD_SIZE)
>> +		pud_size_align = true;
> 
> This code will have duplicates in the next patch, so how about checking
> this in a separate check routine?

Good suggestion,  thanks
-- 
Mike Kravetz

> 
> Thanks,
> Naoya Horiguchi
>