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SubjectRe: [HMM v13 08/18] mm/hmm: heterogeneous memory management (HMM for short)
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On 19/11/16 05:18, Jérôme Glisse wrote:
> HMM provides 3 separate functionality :
> - Mirroring: synchronize CPU page table and device page table
> - Device memory: allocating struct page for device memory
> - Migration: migrating regular memory to device memory
>
> This patch introduces some common helpers and definitions to all of
> those 3 functionality.
>
> Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> Signed-off-by: Jatin Kumar <jakumar@nvidia.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Mark Hairgrove <mhairgrove@nvidia.com>
> Signed-off-by: Sherry Cheung <SCheung@nvidia.com>
> Signed-off-by: Subhash Gutti <sgutti@nvidia.com>
> ---
> MAINTAINERS | 7 +++
> include/linux/hmm.h | 139 +++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/mm_types.h | 5 ++
> kernel/fork.c | 2 +
> mm/Kconfig | 11 ++++
> mm/Makefile | 1 +
> mm/hmm.c | 86 +++++++++++++++++++++++++++++
> 7 files changed, 251 insertions(+)
> create mode 100644 include/linux/hmm.h
> create mode 100644 mm/hmm.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f593300..41cd63d 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5582,6 +5582,13 @@ S: Supported
> F: drivers/scsi/hisi_sas/
> F: Documentation/devicetree/bindings/scsi/hisilicon-sas.txt
>
> +HMM - Heterogeneous Memory Management
> +M: Jérôme Glisse <jglisse@redhat.com>
> +L: linux-mm@kvack.org
> +S: Maintained
> +F: mm/hmm*
> +F: include/linux/hmm*
> +
> HOST AP DRIVER
> M: Jouni Malinen <j@w1.fi>
> L: hostap@shmoo.com (subscribers-only)
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> new file mode 100644
> index 0000000..54dd529
> --- /dev/null
> +++ b/include/linux/hmm.h
> @@ -0,0 +1,139 @@
> +/*
> + * Copyright 2013 Red Hat Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * Authors: Jérôme Glisse <jglisse@redhat.com>
> + */
> +/*
> + * HMM provides 3 separate functionality :
> + * - Mirroring: synchronize CPU page table and device page table
> + * - Device memory: allocating struct page for device memory
> + * - Migration: migrating regular memory to device memory
> + *
> + * Each can be use independently from the others.
> + *
> + *
> + * Mirroring:
> + *
> + * HMM provide helpers to mirror process address space on a device. For this it
> + * provides several helpers to order device page table update in respect to CPU
> + * page table update. Requirement is that for any given virtual address the CPU
> + * and device page table can not point to different physical page. It uses the
> + * mmu_notifier API and introduce virtual address range lock which block CPU
> + * page table update for a range while the device page table is being updated.
> + * Usage pattern is:
> + *
> + * hmm_vma_range_lock(vma, start, end);
> + * // snap shot CPU page table
> + * // update device page table from snapshot
> + * hmm_vma_range_unlock(vma, start, end);
> + *
> + * Any CPU page table update that conflict with a range lock will wait until
> + * range is unlock. This garanty proper serialization of CPU and device page
> + * table update.
> + *
> + *
> + * Device memory:
> + *
> + * HMM provides helpers to help leverage device memory either addressable like
> + * regular memory by the CPU or un-addressable at all. In both case the device
> + * memory is associated to dedicated structs page (which are allocated like for
> + * hotplug memory). Device memory management is under the responsability of the
> + * device driver. HMM only allocate and initialize the struct pages associated
> + * with the device memory.
> + *
> + * Allocating struct page for device memory allow to use device memory allmost
> + * like any regular memory. Unlike regular memory it can not be added to the
> + * lru, nor can any memory allocation can use device memory directly. Device
> + * memory will only end up to be use in a process if device driver migrate some
in use
> + * of the process memory from regular memory to device memory.
> + *

A process can never directly allocate device memory?

> + *
> + * Migration:
> + *
> + * Existing memory migration mechanism (mm/migrate.c) does not allow to use
> + * something else than the CPU to copy from source to destination memory. More
> + * over existing code is not tailor to drive migration from process virtual
tailored
> + * address rather than from list of pages. Finaly the migration flow does not
Finally
> + * allow for graceful failure at different step of the migration process.
> + *
> + * HMM solves all of the above though simple API :
> + *
> + * hmm_vma_migrate(vma, start, end, ops);
> + *
> + * With ops struct providing 2 callback alloc_and_copy() which allocated the
> + * destination memory and initialize it using source memory. Migration can fail
> + * after this step and thus last callback finalize_and_map() allow the device
> + * driver to know which page were successfully migrated and which were not.
> + *
> + * This can easily be use outside of HMM intended use case.
> + *

I think it is a good API to have

> + *
> + * This header file contain all the API related to this 3 functionality and
> + * each functions and struct are more thouroughly documented in below comments.
> + */
> +#ifndef LINUX_HMM_H
> +#define LINUX_HMM_H
> +
> +#include <linux/kconfig.h>
> +
> +#if IS_ENABLED(CONFIG_HMM)
> +
> +
> +/*
> + * hmm_pfn_t - HMM use its own pfn type to keep several flags per page
uses
> + *
> + * Flags:
> + * HMM_PFN_VALID: pfn is valid
> + * HMM_PFN_WRITE: CPU page table have the write permission set
has
> + */
> +typedef unsigned long hmm_pfn_t;
> +
> +#define HMM_PFN_VALID (1 << 0)
> +#define HMM_PFN_WRITE (1 << 1)
> +#define HMM_PFN_SHIFT 2
> +
> +static inline struct page *hmm_pfn_to_page(hmm_pfn_t pfn)
> +{
> + if (!(pfn & HMM_PFN_VALID))
> + return NULL;
> + return pfn_to_page(pfn >> HMM_PFN_SHIFT);
> +}
> +
> +static inline unsigned long hmm_pfn_to_pfn(hmm_pfn_t pfn)
> +{
> + if (!(pfn & HMM_PFN_VALID))
> + return -1UL;
> + return (pfn >> HMM_PFN_SHIFT);
> +}
> +

What is pfn_to_pfn? I presume it means CPU PFN to device PFN
or is it the reverse? Please add some comments

> +static inline hmm_pfn_t hmm_pfn_from_page(struct page *page)
> +{
> + return (page_to_pfn(page) << HMM_PFN_SHIFT) | HMM_PFN_VALID;
> +}
> +
> +static inline hmm_pfn_t hmm_pfn_from_pfn(unsigned long pfn)
> +{
> + return (pfn << HMM_PFN_SHIFT) | HMM_PFN_VALID;
> +}
> +

Same as above

> +
> +/* Below are for HMM internal use only ! Not to be use by device driver ! */
> +void hmm_mm_destroy(struct mm_struct *mm);
> +
> +#else /* IS_ENABLED(CONFIG_HMM) */
> +
> +/* Below are for HMM internal use only ! Not to be use by device driver ! */
> +static inline void hmm_mm_destroy(struct mm_struct *mm) {}
> +
> +#endif /* IS_ENABLED(CONFIG_HMM) */
> +#endif /* LINUX_HMM_H */
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4a8aced..4effdbf 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -23,6 +23,7 @@
>
> struct address_space;
> struct mem_cgroup;
> +struct hmm;
>
> #define USE_SPLIT_PTE_PTLOCKS (NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS)
> #define USE_SPLIT_PMD_PTLOCKS (USE_SPLIT_PTE_PTLOCKS && \
> @@ -516,6 +517,10 @@ struct mm_struct {
> atomic_long_t hugetlb_usage;
> #endif
> struct work_struct async_put_work;
> +#if IS_ENABLED(CONFIG_HMM)
> + /* HMM need to track few things per mm */
> + struct hmm *hmm;
> +#endif
> };
>
> static inline void mm_init_cpumask(struct mm_struct *mm)
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 690a1aad..af0eec8 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>
> @@ -702,6 +703,7 @@ void __mmdrop(struct mm_struct *mm)
> BUG_ON(mm == &init_mm);
> mm_free_pgd(mm);
> destroy_context(mm);
> + hmm_mm_destroy(mm);
> mmu_notifier_mm_destroy(mm);
> check_mm(mm);
> free_mm(mm);
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 0a21411..be18cc2 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -289,6 +289,17 @@ config MIGRATION
> config ARCH_ENABLE_HUGEPAGE_MIGRATION
> bool
>
> +config HMM
> + bool "Heterogeneous memory management (HMM)"
> + depends on MMU
> + default n
> + help
> + Heterogeneous memory management, set of helpers for:
> + - mirroring of process address space on a device
> + - using device memory transparently inside a process
> +
> + If unsure, say N to disable HMM.
> +

It would be nice to split this into HMM, HMM_MIGRATE and HMM_MIRROR

> config PHYS_ADDR_T_64BIT
> def_bool 64BIT || ARCH_PHYS_ADDR_T_64BIT
>
> diff --git a/mm/Makefile b/mm/Makefile
> index 2ca1faf..6ac1284 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_FAILSLAB) += failslab.o
> obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
> obj-$(CONFIG_MEMTEST) += memtest.o
> obj-$(CONFIG_MIGRATION) += migrate.o
> +obj-$(CONFIG_HMM) += hmm.o
> obj-$(CONFIG_QUICKLIST) += quicklist.o
> obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o
> obj-$(CONFIG_PAGE_COUNTER) += page_counter.o
> diff --git a/mm/hmm.c b/mm/hmm.c
> new file mode 100644
> index 0000000..342b596
> --- /dev/null
> +++ b/mm/hmm.c
> @@ -0,0 +1,86 @@
> +/*
> + * Copyright 2013 Red Hat Inc.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * Authors: Jérôme Glisse <jglisse@redhat.com>
> + */
> +/*
> + * Refer to include/linux/hmm.h for informations about heterogeneous memory
> + * management or HMM for short.
> + */
> +#include <linux/mm.h>
> +#include <linux/hmm.h>
> +#include <linux/slab.h>
> +#include <linux/sched.h>
> +
> +/*
> + * struct hmm - HMM per mm struct
> + *
> + * @mm: mm struct this HMM struct is bound to
> + */
> +struct hmm {
> + struct mm_struct *mm;
> +};
> +
> +/*
> + * hmm_register - register HMM against an mm (HMM internal)
> + *
> + * @mm: mm struct to attach to
> + *
> + * This is not intended to be use directly by device driver but by other HMM
> + * component. It allocates an HMM struct if mm does not have one and initialize
> + * it.
> + */
> +static struct hmm *hmm_register(struct mm_struct *mm)
> +{
> + struct hmm *hmm = NULL;
> +
> + if (!mm->hmm) {
> + hmm = kmalloc(sizeof(*hmm), GFP_KERNEL);
> + if (!hmm)
> + return NULL;
> + hmm->mm = mm;
> + }
> +
> + spin_lock(&mm->page_table_lock);
> + if (!mm->hmm)
> + /*
> + * The hmm struct can only be free once mm_struct goes away
> + * hence we should always have pre-allocated an new hmm struct
> + * above.
> + */
> + mm->hmm = hmm;
> + else if (hmm)
> + kfree(hmm);
> + hmm = mm->hmm;
> + spin_unlock(&mm->page_table_lock);
> +
> + return hmm;
> +}
> +
> +void hmm_mm_destroy(struct mm_struct *mm)
> +{
> + struct hmm *hmm;
> +
> + /*
> + * We should not need to lock here as no one should be able to register
> + * a new HMM while an mm is being destroy. But just to be safe ...
> + */
> + spin_lock(&mm->page_table_lock);
> + hmm = mm->hmm;
> + mm->hmm = NULL;
> + spin_unlock(&mm->page_table_lock);
> + if (!hmm)
> + return;
> +

kfree can deal with NULL pointers, you can remove the if check

> + kfree(hmm);
> +}
>

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