Subject: Re: [PATCH 3/3] powerpc/mm: Add page soft dirty tracking

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sat, 17 Oct 2015 17:49:34 +0530

Laurent Dufour <[email-masked]> writes:

> User space checkpoint and restart tool (CRIU) needs the page's change
> to be soft tracked. This allows to do a pre checkpoint and then dump
> only touched pages.
>
> This is done by using a newly assigned PTE bit (_PAGE_SOFT_DIRTY) when
> the page is backed in memory, and a new _PAGE_SWP_SOFT_DIRTY bit when
> the page is swapped out.
>
> The _PAGE_SWP_SOFT_DIRTY bit is dynamically put after the swap type
> in the swap pte. A check is added to ensure that the bit is not
> overwritten by _PAGE_HPTEFLAGS.
>
> Signed-off-by: Laurent Dufour <[email-masked]>
> CC: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/Kconfig                     |  2 ++
>  arch/powerpc/include/asm/pgtable-ppc64.h | 13 +++++++++--
>  arch/powerpc/include/asm/pgtable.h       | 40 +++++++++++++++++++++++++++++++-
>  arch/powerpc/include/asm/pte-book3e.h    |  1 +
>  arch/powerpc/include/asm/pte-common.h    |  5 ++--
>  arch/powerpc/include/asm/pte-hash64.h    |  1 +
>  6 files changed, 57 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 9a7057ec2154..73a4a36a6b38 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -559,6 +559,7 @@ choice
>
>  config PPC_4K_PAGES
>  	bool "4k page size"
> +	select HAVE_ARCH_SOFT_DIRTY if CHECKPOINT_RESTORE && PPC_BOOK3S
>
>  config PPC_16K_PAGES
>  	bool "16k page size"
> @@ -567,6 +568,7 @@ config PPC_16K_PAGES
>  config PPC_64K_PAGES
>  	bool "64k page size"
>  	depends on !PPC_FSL_BOOK3E && (44x || PPC_STD_MMU_64 || PPC_BOOK3E_64)
> +	select HAVE_ARCH_SOFT_DIRTY if CHECKPOINT_RESTORE && PPC_BOOK3S
>
>  config PPC_256K_PAGES
>  	bool "256k page size"
> diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
> index fa1dfb7f7b48..2738bf4a8c55 100644
> --- a/arch/powerpc/include/asm/pgtable-ppc64.h
> +++ b/arch/powerpc/include/asm/pgtable-ppc64.h
> @@ -315,7 +315,8 @@ static inline void pte_clear(struct mm_struct *mm, unsigned long addr,
>  static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
>  {
>  	unsigned long bits = pte_val(entry) &
> -		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
> +		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC |
> +		 _PAGE_SOFT_DIRTY);
>
>  #ifdef PTE_ATOMIC_UPDATES
>  	unsigned long old, tmp;
> @@ -354,6 +355,7 @@ static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
>  	 * We filter HPTEFLAGS on set_pte.			\
>  	 */							\
>  	BUILD_BUG_ON(_PAGE_HPTEFLAGS & (0x1f << _PAGE_BIT_SWAP_TYPE)); \
> +	BUILD_BUG_ON(_PAGE_HPTEFLAGS & _PAGE_SWP_SOFT_DIRTY);	\
>  	} while (0)
>  /*
>   * on pte we don't need handle RADIX_TREE_EXCEPTIONAL_SHIFT;
> @@ -371,6 +373,8 @@ static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
>
>  void pgtable_cache_add(unsigned shift, void (*ctor)(void *));
>  void pgtable_cache_init(void);
> +
> +#define _PAGE_SWP_SOFT_DIRTY	(1UL << (SWP_TYPE_BITS + _PAGE_BIT_SWAP_TYPE))
>  #endif /* __ASSEMBLY__ */
>
>  /*
> @@ -389,7 +393,7 @@ void pgtable_cache_init(void);
>   */
>  #define _HPAGE_CHG_MASK (PTE_RPN_MASK | _PAGE_HPTEFLAGS |		\
>  			 _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_SPLITTING | \
> -			 _PAGE_THP_HUGE)
> +			 _PAGE_THP_HUGE | _PAGE_SOFT_DIRTY)
>
>  #ifndef __ASSEMBLY__
>  /*
> @@ -513,6 +517,11 @@ static inline pte_t *pmdp_ptep(pmd_t *pmd)
>  #define pmd_mkyoung(pmd)	pte_pmd(pte_mkyoung(pmd_pte(pmd)))
>  #define pmd_mkwrite(pmd)	pte_pmd(pte_mkwrite(pmd_pte(pmd)))
>
> +#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
> +#define pmd_soft_dirty(pmd)	pte_soft_dirty(pmd_pte(pmd))
> +#define pmd_mksoft_dirty(pmd)	pte_pmd(pte_mksoft_dirty(pmd_pte(pmd)))
> +#endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
> +
>  #define __HAVE_ARCH_PMD_WRITE
>  #define pmd_write(pmd)		pte_write(pmd_pte(pmd))
>
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 0717693c8428..88baad3d66e2 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -38,6 +38,44 @@ static inline int pte_special(pte_t pte)	{ return pte_val(pte) & _PAGE_SPECIAL;
>  static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
>  static inline pgprot_t pte_pgprot(pte_t pte)	{ return __pgprot(pte_val(pte) & PAGE_PROT_BITS); }
>
> +#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
> +static inline int pte_soft_dirty(pte_t pte)
> +{
> +	return pte_val(pte) & _PAGE_SOFT_DIRTY;
> +}
> +static inline pte_t pte_mksoft_dirty(pte_t pte)
> +{
> +	pte_val(pte) |= _PAGE_SOFT_DIRTY;
> +	return pte;

This will break after
https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-October/135298.html

A good option is to drop this patch from the series and let Andrew take
the first two patches. You can send an updated version of patch 3 against
linux-powerpc tree once Michael pulls that series to his tree. 

> +}
> +
> +static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
> +{
> +	pte_val(pte) |= _PAGE_SWP_SOFT_DIRTY;
> +	return pte;
> +}
> +static inline int pte_swp_soft_dirty(pte_t pte)
> +{
> +	return pte_val(pte) & _PAGE_SWP_SOFT_DIRTY;
> +}
> +static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
> +{
> +	pte_val(pte) &= ~_PAGE_SWP_SOFT_DIRTY;
> +	return pte;
> +}
> +
> +static inline pte_t pte_clear_flags(pte_t pte, pte_basic_t clear)
> +{
> +	pte_val(pte) &= ~clear;
> +	return pte;
> +}
> +static inline pmd_t pmd_clear_flags(pmd_t pmd, unsigned long clear)
> +{
> +	pmd_val(pmd) &= ~clear;
> +	return pmd;
> +}
> +#endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
> +
>  #ifdef CONFIG_NUMA_BALANCING
>  /*
>   * These work without NUMA balancing but the kernel does not care. See the
> @@ -89,7 +127,7 @@ static inline pte_t pte_mkwrite(pte_t pte) {
>  	pte_val(pte) &= ~_PAGE_RO;
>  	pte_val(pte) |= _PAGE_RW; return pte; }
>  static inline pte_t pte_mkdirty(pte_t pte) {
> -	pte_val(pte) |= _PAGE_DIRTY; return pte; }
> +	pte_val(pte) |= _PAGE_DIRTY | _PAGE_SOFT_DIRTY; return pte; }
>  static inline pte_t pte_mkyoung(pte_t pte) {
>  	pte_val(pte) |= _PAGE_ACCESSED; return pte; }
>  static inline pte_t pte_mkspecial(pte_t pte) {
> diff --git a/arch/powerpc/include/asm/pte-book3e.h b/arch/powerpc/include/asm/pte-book3e.h
> index 8d8473278d91..df5581f817f6 100644
> --- a/arch/powerpc/include/asm/pte-book3e.h
> +++ b/arch/powerpc/include/asm/pte-book3e.h
> @@ -57,6 +57,7 @@
>
>  #define _PAGE_HASHPTE	0
>  #define _PAGE_BUSY	0
> +#define _PAGE_SOFT_DIRTY	0
>
>  #define _PAGE_SPECIAL	_PAGE_SW0
>
> diff --git a/arch/powerpc/include/asm/pte-common.h b/arch/powerpc/include/asm/pte-common.h
> index 71537a319fc8..1bf670996df5 100644
> --- a/arch/powerpc/include/asm/pte-common.h
> +++ b/arch/powerpc/include/asm/pte-common.h
> @@ -94,13 +94,14 @@ extern unsigned long bad_call_to_PMD_PAGE_SIZE(void);
>   * pgprot changes
>   */
>  #define _PAGE_CHG_MASK	(PTE_RPN_MASK | _PAGE_HPTEFLAGS | _PAGE_DIRTY | \
> -                         _PAGE_ACCESSED | _PAGE_SPECIAL)
> +			 _PAGE_ACCESSED | _PAGE_SPECIAL | _PAGE_SOFT_DIRTY)
>
>  /* Mask of bits returned by pte_pgprot() */
>  #define PAGE_PROT_BITS	(_PAGE_GUARDED | _PAGE_COHERENT | _PAGE_NO_CACHE | \
>  			 _PAGE_WRITETHRU | _PAGE_ENDIAN | _PAGE_4K_PFN | \
>  			 _PAGE_USER | _PAGE_ACCESSED | _PAGE_RO | \
> -			 _PAGE_RW | _PAGE_HWWRITE | _PAGE_DIRTY | _PAGE_EXEC)
> +			 _PAGE_RW | _PAGE_HWWRITE | _PAGE_DIRTY | \
> +			 _PAGE_EXEC | _PAGE_SOFT_DIRTY)
>
>  /*
>   * We define 2 sets of base prot bits, one for basic pages (ie,
> diff --git a/arch/powerpc/include/asm/pte-hash64.h b/arch/powerpc/include/asm/pte-hash64.h
> index ef612c160da7..19ffd150957f 100644
> --- a/arch/powerpc/include/asm/pte-hash64.h
> +++ b/arch/powerpc/include/asm/pte-hash64.h
> @@ -19,6 +19,7 @@
>  #define _PAGE_BIT_SWAP_TYPE	2
>  #define _PAGE_EXEC		0x0004 /* No execute on POWER4 and newer (we invert) */
>  #define _PAGE_GUARDED		0x0008
> +#define _PAGE_SOFT_DIRTY	0x0010 /* software dirty tracking */
>  /* We can derive Memory coherence from _PAGE_NO_CACHE */
>  #define _PAGE_NO_CACHE		0x0020 /* I: cache inhibit */
>  #define _PAGE_WRITETHRU		0x0040 /* W: cache write-through */
> -- 
> 1.9.1

-aneesh