Re: [PATCH 05/36] HMM: introduce heterogeneous memory management v3.

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

j.glisse@gmail.com writes:

> From: Jérôme Glisse <jglisse@redhat.com>
>
> This patch only introduce core HMM functions for registering a new
> mirror and stopping a mirror as well as HMM device registering and
> unregistering.
>
> The lifecycle of HMM object is handled differently then the one of
> mmu_notifier because unlike mmu_notifier there can be concurrent
> call from both mm code to HMM code and/or from device driver code
> to HMM code. Moreover lifetime of HMM can be uncorrelated from the
> lifetime of the process that is being mirror (GPU might take longer
> time to cleanup).
>

......

> +struct hmm_device_ops {
> +	/* release() - mirror must stop using the address space.
> +	 *
> +	 * @mirror: The mirror that link process address space with the device.
> +	 *
> +	 * When this is call, device driver must kill all device thread using

s/call/called, ?

> +	 * this mirror. Also, this callback is the last thing call by HMM and
> +	 * HMM will not access the mirror struct after this call (ie no more
> +	 * dereference of it so it is safe for the device driver to free it).
> +	 * It is call either from :
> +	 *   - mm dying (all process using this mm exiting).
> +	 *   - hmm_mirror_unregister() (if no other thread holds a reference)
> +	 *   - outcome of some device error reported by any of the device
> +	 *     callback against that mirror.
> +	 */
> +	void (*release)(struct hmm_mirror *mirror);
> +};
> +
> +
> +/* struct hmm - per mm_struct HMM states.
> + *
> + * @mm: The mm struct this hmm is associated with.
> + * @mirrors: List of all mirror for this mm (one per device).
> + * @vm_end: Last valid address for this mm (exclusive).
> + * @kref: Reference counter.
> + * @rwsem: Serialize the mirror list modifications.
> + * @mmu_notifier: The mmu_notifier of this mm.
> + * @rcu: For delayed cleanup call from mmu_notifier.release() callback.
> + *
> + * For each process address space (mm_struct) there is one and only one hmm
> + * struct. hmm functions will redispatch to each devices the change made to
> + * the process address space.
> + *
> + * Device driver must not access this structure other than for getting the
> + * mm pointer.
> + */

.....

>  #ifndef AT_VECTOR_SIZE_ARCH
>  #define AT_VECTOR_SIZE_ARCH 0
>  #endif
> @@ -451,6 +455,16 @@ struct mm_struct {
>  #ifdef CONFIG_MMU_NOTIFIER
>  	struct mmu_notifier_mm *mmu_notifier_mm;
>  #endif
> +#ifdef CONFIG_HMM
> +	/*
> +	 * hmm always register an mmu_notifier we rely on mmu notifier to keep
> +	 * refcount on mm struct as well as forbiding registering hmm on a
> +	 * dying mm
> +	 *
> +	 * This field is set with mmap_sem old in write mode.

s/old/held/ ?


> +	 */
> +	struct hmm *hmm;
> +#endif
>  #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
>  	pgtable_t pmd_huge_pte; /* protected by page_table_lock */
>  #endif
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 0e0ae9a..4083be7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -27,6 +27,7 @@
>  #include <linux/binfmts.h>
>  #include <linux/mman.h>
>  #include <linux/mmu_notifier.h>
> +#include <linux/hmm.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/vmacache.h>
> @@ -597,6 +598,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
>  	mm_init_aio(mm);
>  	mm_init_owner(mm, p);
>  	mmu_notifier_mm_init(mm);
> +	hmm_mm_init(mm);
>  	clear_tlb_flush_pending(mm);
>  #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
>  	mm->pmd_huge_pte = NULL;
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 52ffb86..189e48f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -653,3 +653,18 @@ config DEFERRED_STRUCT_PAGE_INIT
>  	  when kswapd starts. This has a potential performance impact on
>  	  processes running early in the lifetime of the systemm until kswapd
>  	  finishes the initialisation.
> +
> +if STAGING
> +config HMM
> +	bool "Enable heterogeneous memory management (HMM)"
> +	depends on MMU
> +	select MMU_NOTIFIER
> +	select GENERIC_PAGE_TABLE

What is GENERIC_PAGE_TABLE ?

> +	default n
> +	help
> +	  Heterogeneous memory management provide infrastructure for a device
> +	  to mirror a process address space into an hardware mmu or into any
> +	  things supporting pagefault like event.
> +
> +	  If unsure, say N to disable hmm.

-aneesh

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