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From: Pavel Tatashin <pasha.tatashin@gmail.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	linux-mm@kvack.org, akpm@linux-foundation.org
Cc: pavel.tatashin@microsoft.com, mhocko@suse.com,
	dave.jiang@intel.com, linux-kernel@vger.kernel.org,
	willy@infradead.org, davem@davemloft.net,
	yi.z.zhang@linux.intel.com, khalid.aziz@oracle.com,
	rppt@linux.vnet.ibm.com, vbabka@suse.cz,
	sparclinux@vger.kernel.org, dan.j.williams@intel.com,
	ldufour@linux.vnet.ibm.com, mgorman@techsingularity.net,
	mingo@kernel.org, kirill.shutemov@linux.intel.com
Subject: Re: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures
Date: Tue, 16 Oct 2018 15:01:11 -0400	[thread overview]
Message-ID: <57c559f6-4858-7a52-7fbb-979caa08f240@gmail.com> (raw)
In-Reply-To: <20181015202656.2171.92963.stgit@localhost.localdomain>



On 10/15/18 4:26 PM, Alexander Duyck wrote:
> This change makes it so that we use the same approach that was already in
> use on Sparc on all the archtectures that support a 64b long.
> 
> This is mostly motivated by the fact that 8 to 10 store/move instructions
> are likely always going to be faster than having to call into a function
> that is not specialized for handling page init.
> 
> An added advantage to doing it this way is that the compiler can get away
> with combining writes in the __init_single_page call. As a result the
> memset call will be reduced to only about 4 write operations, or at least
> that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and
> count/mapcount seem to be cancelling out at least 4 of the 8 assignments on
> my system.
> 
> One change I had to make to the function was to reduce the minimum page
> size to 56 to support some powerpc64 configurations.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>


I have tested on Broadcom's Stingray cpu with 48G RAM:
__init_single_page() takes 19.30ns / 64-byte struct page
Wit the change it takes 17.33ns / 64-byte struct page

Please add this data and also the data from Intel to the description.

Thank you,
Pavel

> ---
>  arch/sparc/include/asm/pgtable_64.h |   30 ------------------------------
>  include/linux/mm.h                  |   34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 1393a8ac596b..22500c3be7a9 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -231,36 +231,6 @@
>  extern struct page *mem_map_zero;
>  #define ZERO_PAGE(vaddr)	(mem_map_zero)
>  
> -/* This macro must be updated when the size of struct page grows above 80
> - * or reduces below 64.
> - * The idea that compiler optimizes out switch() statement, and only
> - * leaves clrx instructions
> - */
> -#define	mm_zero_struct_page(pp) do {					\
> -	unsigned long *_pp = (void *)(pp);				\
> -									\
> -	 /* Check that struct page is either 64, 72, or 80 bytes */	\
> -	BUILD_BUG_ON(sizeof(struct page) & 7);				\
> -	BUILD_BUG_ON(sizeof(struct page) < 64);				\
> -	BUILD_BUG_ON(sizeof(struct page) > 80);				\
> -									\
> -	switch (sizeof(struct page)) {					\
> -	case 80:							\
> -		_pp[9] = 0;	/* fallthrough */			\
> -	case 72:							\
> -		_pp[8] = 0;	/* fallthrough */			\
> -	default:							\
> -		_pp[7] = 0;						\
> -		_pp[6] = 0;						\
> -		_pp[5] = 0;						\
> -		_pp[4] = 0;						\
> -		_pp[3] = 0;						\
> -		_pp[2] = 0;						\
> -		_pp[1] = 0;						\
> -		_pp[0] = 0;						\
> -	}								\
> -} while (0)
> -
>  /* PFNs are real physical page numbers.  However, mem_map only begins to record
>   * per-page information starting at pfn_base.  This is to handle systems where
>   * the first physical page in the machine is at some huge physical address,
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index bb0de406f8e7..ec6e57a0c14e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -102,8 +102,42 @@ static inline void set_max_mapnr(unsigned long limit) { }
>   * zeroing by defining this macro in <asm/pgtable.h>.
>   */

The comment above becomes outdated. Please change, we use optimized
mm_zero_struct_page on every 64-bit platform.

>  #ifndef mm_zero_struct_page
> +#if BITS_PER_LONG == 64
> +/* This function must be updated when the size of struct page grows above 80
> + * or reduces below 64. The idea that compiler optimizes out switch()
> + * statement, and only leaves move/store instructions
> + */
> +#define	mm_zero_struct_page(pp) __mm_zero_struct_page(pp)
> +static inline void __mm_zero_struct_page(struct page *page)
> +{
> +	unsigned long *_pp = (void *)page;
> +
> +	 /* Check that struct page is either 56, 64, 72, or 80 bytes */
> +	BUILD_BUG_ON(sizeof(struct page) & 7);
> +	BUILD_BUG_ON(sizeof(struct page) < 56);
> +	BUILD_BUG_ON(sizeof(struct page) > 80);
> +
> +	switch (sizeof(struct page)) {
> +	case 80:
> +		_pp[9] = 0;	/* fallthrough */
> +	case 72:
> +		_pp[8] = 0;	/* fallthrough */
> +	default:
> +		_pp[7] = 0;	/* fallthrough */
> +	case 56:
> +		_pp[6] = 0;
> +		_pp[5] = 0;
> +		_pp[4] = 0;
> +		_pp[3] = 0;
> +		_pp[2] = 0;
> +		_pp[1] = 0;
> +		_pp[0] = 0;
> +	}
> +}
> +#else
>  #define mm_zero_struct_page(pp)  ((void)memset((pp), 0, sizeof(struct page)))
>  #endif
> +#endif
>  
>  /*
>   * Default maximum number of active map areas, this limits the number of vmas
> 

  reply	other threads:[~2018-10-16 19:01 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-15 20:26 [mm PATCH v3 0/6] Deferred page init improvements Alexander Duyck
2018-10-15 20:26 ` [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures Alexander Duyck
2018-10-16 19:01   ` Pavel Tatashin [this message]
2018-10-17  7:30     ` Mike Rapoport
2018-10-17 14:52       ` Alexander Duyck
2018-10-17  8:47   ` Michal Hocko
2018-10-17 15:07     ` Alexander Duyck
2018-10-17 15:12       ` Pavel Tatashin
2018-10-17 15:40         ` David Laight
2018-10-17 16:31           ` Alexander Duyck
2018-10-17 17:08             ` Pavel Tatashin
2018-10-17 16:34       ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 2/6] mm: Drop meminit_pfn_in_nid as it is redundant Alexander Duyck
2018-10-16 20:33   ` Pavel Tatashin
2018-10-16 20:49     ` Alexander Duyck
2018-10-16 21:06       ` Pavel Tatashin
2018-10-17  9:04   ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 3/6] mm: Use memblock/zone specific iterator for handling deferred page init Alexander Duyck
2018-10-17  9:11   ` Michal Hocko
2018-10-17 15:17     ` Alexander Duyck
2018-10-17 16:42   ` Mike Rapoport
2018-10-15 20:27 ` [mm PATCH v3 4/6] mm: Move hot-plug specific memory init into separate functions and optimize Alexander Duyck
2018-10-17  9:18   ` Michal Hocko
2018-10-17 15:26     ` Alexander Duyck
2018-10-24 12:36       ` Michal Hocko
2018-10-24 15:08         ` Alexander Duyck
2018-10-24 15:27           ` Michal Hocko
2018-10-24 17:35             ` Alexander Duyck
2018-10-25 12:41               ` Michal Hocko
2018-10-15 20:27 ` [mm PATCH v3 5/6] mm: Use common iterator for deferred_init_pages and deferred_free_pages Alexander Duyck
2018-10-15 20:27 ` [mm PATCH v3 6/6] mm: Add reserved flag setting to set_page_links Alexander Duyck

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