linux-kernel - Re: [patch 2/2] [PATCH] mm: Save soft-dirty bits on file pages

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Message-Id: <20130807132812.60ad4bfe85127794094d385e@linux-foundation.org>
Date:	Wed, 7 Aug 2013 13:28:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	luto@...capital.net, gorcunov@...nvz.org, xemul@...allels.com,
	mpm@...enic.com, xiaoguangrong@...ux.vnet.ibm.com,
	mtosatti@...hat.com, kosaki.motohiro@...il.com,
	sfr@...b.auug.org.au, peterz@...radead.org,
	aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [patch 2/2] [PATCH] mm: Save soft-dirty bits on file pages

On Wed, 31 Jul 2013 00:41:56 +0400 Cyrill Gorcunov <gorcunov@...il.com> wrote:

> +#define pte_to_pgoff(pte)						\
> +	((((pte).pte_low >> (PTE_FILE_SHIFT1))				\
> +	  & ((1U << PTE_FILE_BITS1) - 1)))				\
> +	+ ((((pte).pte_low >> (PTE_FILE_SHIFT2))			\
> +	    & ((1U << PTE_FILE_BITS2) - 1))				\
> +	   << (PTE_FILE_BITS1))						\
> +	+ ((((pte).pte_low >> (PTE_FILE_SHIFT3))			\
> +	    & ((1U << PTE_FILE_BITS3) - 1))				\
> +	   << (PTE_FILE_BITS1 + PTE_FILE_BITS2))			\
> +	+ ((((pte).pte_low >> (PTE_FILE_SHIFT4)))			\
> +	    << (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3))
> +
> +#define pgoff_to_pte(off)						\
> +	((pte_t) { .pte_low =						\
> +	 ((((off)) & ((1U << PTE_FILE_BITS1) - 1)) << PTE_FILE_SHIFT1)	\
> +	 + ((((off) >> PTE_FILE_BITS1)					\
> +	     & ((1U << PTE_FILE_BITS2) - 1))				\
> +	    << PTE_FILE_SHIFT2)						\
> +	 + ((((off) >> (PTE_FILE_BITS1 + PTE_FILE_BITS2))		\
> +	     & ((1U << PTE_FILE_BITS3) - 1))				\
> +	    << PTE_FILE_SHIFT3)						\
> +	 + ((((off) >>							\
> +	      (PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)))	\
> +	    << PTE_FILE_SHIFT4)						\
> +	 + _PAGE_FILE })

Good god.

I wonder if these can be turned into out-of-line functions in some form
which humans can understand.

or

#define pte_to_pgoff(pte)
	frob(pte, PTE_FILE_SHIFT1, PTE_FILE_BITS1) +
	frob(PTE_FILE_SHIFT2, PTE_FILE_BITS2) +
	frob(PTE_FILE_SHIFT3, PTE_FILE_BITS3) +
	frob(PTE_FILE_SHIFT4, PTE_FILE_BITS1 + PTE_FILE_BITS2 + PTE_FILE_BITS3)


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