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Subject[PATCH 01/10] mm: turn migrate_vma upside down
Date
There isn't any good reason to pass callbacks to migrate_vma.  Instead
we can just export the three steps done by this function to drivers and
let them sequence the operation without callbacks. This removes a lot
of boilerplate code as-is, and will allow the drivers to drastically
improve code flow and error handling further on.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
---
Documentation/vm/hmm.rst | 55 +-----
drivers/gpu/drm/nouveau/nouveau_dmem.c | 122 +++++++------
include/linux/migrate.h | 118 ++----------
mm/migrate.c | 244 +++++++++++--------------
4 files changed, 195 insertions(+), 344 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index e63c11f7e0e0..4f81c77059e3 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -339,58 +339,9 @@ Migration to and from device memory
===================================

Because the CPU cannot access device memory, migration must use the device DMA
-engine to perform copy from and to device memory. For this we need a new
-migration helper::
-
- int migrate_vma(const struct migrate_vma_ops *ops,
- struct vm_area_struct *vma,
- unsigned long mentries,
- unsigned long start,
- unsigned long end,
- unsigned long *src,
- unsigned long *dst,
- void *private);
-
-Unlike other migration functions it works on a range of virtual address, there
-are two reasons for that. First, device DMA copy has a high setup overhead cost
-and thus batching multiple pages is needed as otherwise the migration overhead
-makes the whole exercise pointless. The second reason is because the
-migration might be for a range of addresses the device is actively accessing.
-
-The migrate_vma_ops struct defines two callbacks. First one (alloc_and_copy())
-controls destination memory allocation and copy operation. Second one is there
-to allow the device driver to perform cleanup operations after migration::
-
- struct migrate_vma_ops {
- void (*alloc_and_copy)(struct vm_area_struct *vma,
- const unsigned long *src,
- unsigned long *dst,
- unsigned long start,
- unsigned long end,
- void *private);
- void (*finalize_and_map)(struct vm_area_struct *vma,
- const unsigned long *src,
- const unsigned long *dst,
- unsigned long start,
- unsigned long end,
- void *private);
- };
-
-It is important to stress that these migration helpers allow for holes in the
-virtual address range. Some pages in the range might not be migrated for all
-the usual reasons (page is pinned, page is locked, ...). This helper does not
-fail but just skips over those pages.
-
-The alloc_and_copy() might decide to not migrate all pages in the
-range (for reasons under the callback control). For those, the callback just
-has to leave the corresponding dst entry empty.
-
-Finally, the migration of the struct page might fail (for file backed page) for
-various reasons (failure to freeze reference, or update page cache, ...). If
-that happens, then the finalize_and_map() can catch any pages that were not
-migrated. Note those pages were still copied to a new page and thus we wasted
-bandwidth but this is considered as a rare event and a price that we are
-willing to pay to keep all the code simpler.
+engine to perform copy from and to device memory. For this we need a new to
+use migrate_vma_setup(), migrate_vma_pages(), and migrate_vma_finalize()
+helpers.


Memory cgroup (memcg) and rss accounting
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 345c63cb752a..38416798abd4 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -131,9 +131,8 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct *vma,
unsigned long *dst_pfns,
unsigned long start,
unsigned long end,
- void *private)
+ struct nouveau_dmem_fault *fault)
{
- struct nouveau_dmem_fault *fault = private;
struct nouveau_drm *drm = fault->drm;
struct device *dev = drm->dev->dev;
unsigned long addr, i, npages = 0;
@@ -230,14 +229,9 @@ nouveau_dmem_fault_alloc_and_copy(struct vm_area_struct *vma,
}
}

-void nouveau_dmem_fault_finalize_and_map(struct vm_area_struct *vma,
- const unsigned long *src_pfns,
- const unsigned long *dst_pfns,
- unsigned long start,
- unsigned long end,
- void *private)
+static void
+nouveau_dmem_fault_finalize_and_map(struct nouveau_dmem_fault *fault)
{
- struct nouveau_dmem_fault *fault = private;
struct nouveau_drm *drm = fault->drm;

if (fault->fence) {
@@ -257,29 +251,35 @@ void nouveau_dmem_fault_finalize_and_map(struct vm_area_struct *vma,
kfree(fault->dma);
}

-static const struct migrate_vma_ops nouveau_dmem_fault_migrate_ops = {
- .alloc_and_copy = nouveau_dmem_fault_alloc_and_copy,
- .finalize_and_map = nouveau_dmem_fault_finalize_and_map,
-};
-
static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
{
struct nouveau_dmem *dmem = page_to_dmem(vmf->page);
unsigned long src[1] = {0}, dst[1] = {0};
+ struct migrate_vma args = {
+ .vma = vmf->vma,
+ .start = vmf->address,
+ .end = vmf->address + PAGE_SIZE,
+ .src = src,
+ .dst = dst,
+ };
struct nouveau_dmem_fault fault = { .drm = dmem->drm };
- int ret;

/*
* FIXME what we really want is to find some heuristic to migrate more
* than just one page on CPU fault. When such fault happens it is very
* likely that more surrounding page will CPU fault too.
*/
- ret = migrate_vma(&nouveau_dmem_fault_migrate_ops, vmf->vma,
- vmf->address, vmf->address + PAGE_SIZE,
- src, dst, &fault);
- if (ret)
+ if (migrate_vma_setup(&args) < 0)
return VM_FAULT_SIGBUS;
+ if (!args.cpages)
+ return 0;
+
+ nouveau_dmem_fault_alloc_and_copy(args.vma, src, dst, args.start,
+ args.end, &fault);
+ migrate_vma_pages(&args);
+ nouveau_dmem_fault_finalize_and_map(&fault);

+ migrate_vma_finalize(&args);
if (dst[0] == MIGRATE_PFN_ERROR)
return VM_FAULT_SIGBUS;

@@ -648,9 +648,8 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct *vma,
unsigned long *dst_pfns,
unsigned long start,
unsigned long end,
- void *private)
+ struct nouveau_migrate *migrate)
{
- struct nouveau_migrate *migrate = private;
struct nouveau_drm *drm = migrate->drm;
struct device *dev = drm->dev->dev;
unsigned long addr, i, npages = 0;
@@ -747,14 +746,9 @@ nouveau_dmem_migrate_alloc_and_copy(struct vm_area_struct *vma,
}
}

-void nouveau_dmem_migrate_finalize_and_map(struct vm_area_struct *vma,
- const unsigned long *src_pfns,
- const unsigned long *dst_pfns,
- unsigned long start,
- unsigned long end,
- void *private)
+static void
+nouveau_dmem_migrate_finalize_and_map(struct nouveau_migrate *migrate)
{
- struct nouveau_migrate *migrate = private;
struct nouveau_drm *drm = migrate->drm;

if (migrate->fence) {
@@ -779,10 +773,15 @@ void nouveau_dmem_migrate_finalize_and_map(struct vm_area_struct *vma,
*/
}

-static const struct migrate_vma_ops nouveau_dmem_migrate_ops = {
- .alloc_and_copy = nouveau_dmem_migrate_alloc_and_copy,
- .finalize_and_map = nouveau_dmem_migrate_finalize_and_map,
-};
+static void nouveau_dmem_migrate_chunk(struct migrate_vma *args,
+ struct nouveau_migrate *migrate)
+{
+ nouveau_dmem_migrate_alloc_and_copy(args->vma, args->src, args->dst,
+ args->start, args->end, migrate);
+ migrate_vma_pages(args);
+ nouveau_dmem_migrate_finalize_and_map(migrate);
+ migrate_vma_finalize(args);
+}

int
nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
@@ -790,40 +789,45 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
unsigned long start,
unsigned long end)
{
- unsigned long *src_pfns, *dst_pfns, npages;
- struct nouveau_migrate migrate = {0};
- unsigned long i, c, max;
- int ret = 0;
-
- npages = (end - start) >> PAGE_SHIFT;
- max = min(SG_MAX_SINGLE_ALLOC, npages);
- src_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
- if (src_pfns == NULL)
- return -ENOMEM;
- dst_pfns = kzalloc(sizeof(long) * max, GFP_KERNEL);
- if (dst_pfns == NULL) {
- kfree(src_pfns);
- return -ENOMEM;
- }
+ unsigned long npages = (end - start) >> PAGE_SHIFT;
+ unsigned long max = min(SG_MAX_SINGLE_ALLOC, npages);
+ struct migrate_vma args = {
+ .vma = vma,
+ .start = start,
+ };
+ struct nouveau_migrate migrate = {
+ .drm = drm,
+ .vma = vma,
+ .npages = npages,
+ };
+ unsigned long c, i;
+ int ret = -ENOMEM;
+
+ args.src = kzalloc(sizeof(long) * max, GFP_KERNEL);
+ if (!args.src)
+ goto out;
+ args.dst = kzalloc(sizeof(long) * max, GFP_KERNEL);
+ if (!args.dst)
+ goto out_free_src;

- migrate.drm = drm;
- migrate.vma = vma;
- migrate.npages = npages;
for (i = 0; i < npages; i += c) {
- unsigned long next;
-
c = min(SG_MAX_SINGLE_ALLOC, npages);
- next = start + (c << PAGE_SHIFT);
- ret = migrate_vma(&nouveau_dmem_migrate_ops, vma, start,
- next, src_pfns, dst_pfns, &migrate);
+ args.end = start + (c << PAGE_SHIFT);
+ ret = migrate_vma_setup(&args);
if (ret)
- goto out;
- start = next;
+ goto out_free_dst;
+
+ if (args.cpages)
+ nouveau_dmem_migrate_chunk(&args, &migrate);
+ args.start = args.end;
}

+ ret = 0;
+out_free_dst:
+ kfree(args.dst);
+out_free_src:
+ kfree(args.src);
out:
- kfree(dst_pfns);
- kfree(src_pfns);
return ret;
}

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 7f04754c7f2b..18156d379ebf 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -182,107 +182,27 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
}

-/*
- * struct migrate_vma_ops - migrate operation callback
- *
- * @alloc_and_copy: alloc destination memory and copy source memory to it
- * @finalize_and_map: allow caller to map the successfully migrated pages
- *
- *
- * The alloc_and_copy() callback happens once all source pages have been locked,
- * unmapped and checked (checked whether pinned or not). All pages that can be
- * migrated will have an entry in the src array set with the pfn value of the
- * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set (other
- * flags might be set but should be ignored by the callback).
- *
- * The alloc_and_copy() callback can then allocate destination memory and copy
- * source memory to it for all those entries (ie with MIGRATE_PFN_VALID and
- * MIGRATE_PFN_MIGRATE flag set). Once these are allocated and copied, the
- * callback must update each corresponding entry in the dst array with the pfn
- * value of the destination page and with the MIGRATE_PFN_VALID and
- * MIGRATE_PFN_LOCKED flags set (destination pages must have their struct pages
- * locked, via lock_page()).
- *
- * At this point the alloc_and_copy() callback is done and returns.
- *
- * Note that the callback does not have to migrate all the pages that are
- * marked with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration
- * from device memory to system memory (ie the MIGRATE_PFN_DEVICE flag is also
- * set in the src array entry). If the device driver cannot migrate a device
- * page back to system memory, then it must set the corresponding dst array
- * entry to MIGRATE_PFN_ERROR. This will trigger a SIGBUS if CPU tries to
- * access any of the virtual addresses originally backed by this page. Because
- * a SIGBUS is such a severe result for the userspace process, the device
- * driver should avoid setting MIGRATE_PFN_ERROR unless it is really in an
- * unrecoverable state.
- *
- * For empty entry inside CPU page table (pte_none() or pmd_none() is true) we
- * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
- * allowing device driver to allocate device memory for those unback virtual
- * address. For this the device driver simply have to allocate device memory
- * and properly set the destination entry like for regular migration. Note that
- * this can still fails and thus inside the device driver must check if the
- * migration was successful for those entry inside the finalize_and_map()
- * callback just like for regular migration.
- *
- * THE alloc_and_copy() CALLBACK MUST NOT CHANGE ANY OF THE SRC ARRAY ENTRIES
- * OR BAD THINGS WILL HAPPEN !
- *
- *
- * The finalize_and_map() callback happens after struct page migration from
- * source to destination (destination struct pages are the struct pages for the
- * memory allocated by the alloc_and_copy() callback). Migration can fail, and
- * thus the finalize_and_map() allows the driver to inspect which pages were
- * successfully migrated, and which were not. Successfully migrated pages will
- * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
- *
- * It is safe to update device page table from within the finalize_and_map()
- * callback because both destination and source page are still locked, and the
- * mmap_sem is held in read mode (hence no one can unmap the range being
- * migrated).
- *
- * Once callback is done cleaning up things and updating its page table (if it
- * chose to do so, this is not an obligation) then it returns. At this point,
- * the HMM core will finish up the final steps, and the migration is complete.
- *
- * THE finalize_and_map() CALLBACK MUST NOT CHANGE ANY OF THE SRC OR DST ARRAY
- * ENTRIES OR BAD THINGS WILL HAPPEN !
- */
-struct migrate_vma_ops {
- void (*alloc_and_copy)(struct vm_area_struct *vma,
- const unsigned long *src,
- unsigned long *dst,
- unsigned long start,
- unsigned long end,
- void *private);
- void (*finalize_and_map)(struct vm_area_struct *vma,
- const unsigned long *src,
- const unsigned long *dst,
- unsigned long start,
- unsigned long end,
- void *private);
+struct migrate_vma {
+ struct vm_area_struct *vma;
+ /*
+ * Both src and dst array must be big enough for
+ * (end - start) >> PAGE_SHIFT entries.
+ *
+ * The src array must not be modified by the caller after
+ * migrate_vma_setup(), and must not change the dst array after
+ * migrate_vma_pages() returns.
+ */
+ unsigned long *dst;
+ unsigned long *src;
+ unsigned long cpages;
+ unsigned long npages;
+ unsigned long start;
+ unsigned long end;
};

-#if defined(CONFIG_MIGRATE_VMA_HELPER)
-int migrate_vma(const struct migrate_vma_ops *ops,
- struct vm_area_struct *vma,
- unsigned long start,
- unsigned long end,
- unsigned long *src,
- unsigned long *dst,
- void *private);
-#else
-static inline int migrate_vma(const struct migrate_vma_ops *ops,
- struct vm_area_struct *vma,
- unsigned long start,
- unsigned long end,
- unsigned long *src,
- unsigned long *dst,
- void *private)
-{
- return -EINVAL;
-}
-#endif /* IS_ENABLED(CONFIG_MIGRATE_VMA_HELPER) */
+int migrate_vma_setup(struct migrate_vma *args);
+void migrate_vma_pages(struct migrate_vma *migrate);
+void migrate_vma_finalize(struct migrate_vma *migrate);

#endif /* CONFIG_MIGRATION */

diff --git a/mm/migrate.c b/mm/migrate.c
index 8992741f10aa..e2565374d330 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2118,16 +2118,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
#endif /* CONFIG_NUMA */

#if defined(CONFIG_MIGRATE_VMA_HELPER)
-struct migrate_vma {
- struct vm_area_struct *vma;
- unsigned long *dst;
- unsigned long *src;
- unsigned long cpages;
- unsigned long npages;
- unsigned long start;
- unsigned long end;
-};
-
static int migrate_vma_collect_hole(unsigned long start,
unsigned long end,
struct mm_walk *walk)
@@ -2578,6 +2568,110 @@ static void migrate_vma_unmap(struct migrate_vma *migrate)
}
}

+/**
+ * migrate_vma_setup() - prepare to migrate a range of memory
+ * @args: contains the vma, start, and and pfns arrays for the migration
+ *
+ * Returns: negative errno on failures, 0 when 0 or more pages were migrated
+ * without an error.
+ *
+ * Prepare to migrate a range of memory virtual address range by collecting all
+ * the pages backing each virtual address in the range, saving them inside the
+ * src array. Then lock those pages and unmap them. Once the pages are locked
+ * and unmapped, check whether each page is pinned or not. Pages that aren't
+ * pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
+ * corresponding src array entry. Then restores any pages that are pinned, by
+ * remapping and unlocking those pages.
+ *
+ * The caller should then allocate destination memory and copy source memory to
+ * it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
+ * flag set). Once these are allocated and copied, the caller must update each
+ * corresponding entry in the dst array with the pfn value of the destination
+ * page and with the MIGRATE_PFN_VALID and MIGRATE_PFN_LOCKED flags set
+ * (destination pages must have their struct pages locked, via lock_page()).
+ *
+ * Note that the caller does not have to migrate all the pages that are marked
+ * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
+ * device memory to system memory. If the caller cannot migrate a device page
+ * back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
+ * consequences for the userspace process, so it must be avoided if at all
+ * possible.
+ *
+ * For empty entries inside CPU page table (pte_none() or pmd_none() is true) we
+ * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
+ * allowing the caller to allocate device memory for those unback virtual
+ * address. For this the caller simply has to allocate device memory and
+ * properly set the destination entry like for regular migration. Note that
+ * this can still fails and thus inside the device driver must check if the
+ * migration was successful for those entries after calling migrate_vma_pages()
+ * just like for regular migration.
+ *
+ * After that, the callers must call migrate_vma_pages() to go over each entry
+ * in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
+ * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
+ * then migrate_vma_pages() to migrate struct page information from the source
+ * struct page to the destination struct page. If it fails to migrate the
+ * struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
+ * src array.
+ *
+ * At this point all successfully migrated pages have an entry in the src
+ * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
+ * array entry with MIGRATE_PFN_VALID flag set.
+ *
+ * Once migrate_vma_pages() returns the caller may inspect which pages were
+ * successfully migrated, and which were not. Successfully migrated pages will
+ * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
+ *
+ * It is safe to update device page table from within the finalize_and_map()
+ * callback because both destination and source page are still locked, and the
+ * mmap_sem is held in read mode (hence no one can unmap the range being
+ * migrated).
+ *
+ * Once the caller is done cleaning up things and updating its page table (if it
+ * chose to do so, this is not an obligation) it finally calls
+ * migrate_vma_finalize() to update the CPU page table to point to new pages
+ * for successfully migrated pages or otherwise restore the CPU page table to
+ * point to the original source pages.
+ */
+int migrate_vma_setup(struct migrate_vma *args)
+{
+ long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
+
+ args->start &= PAGE_MASK;
+ args->end &= PAGE_MASK;
+ if (!args->vma || is_vm_hugetlb_page(args->vma) ||
+ (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
+ return -EINVAL;
+ if (nr_pages <= 0)
+ return -EINVAL;
+ if (args->start < args->vma->vm_start ||
+ args->start >= args->vma->vm_end)
+ return -EINVAL;
+ if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
+ return -EINVAL;
+ if (!args->src || !args->dst)
+ return -EINVAL;
+
+ memset(args->src, 0, sizeof(*args->src) * nr_pages);
+ args->cpages = 0;
+ args->npages = 0;
+
+ migrate_vma_collect(args);
+ if (args->cpages)
+ migrate_vma_prepare(args);
+ if (args->cpages)
+ migrate_vma_unmap(args);
+
+ /*
+ * At this point pages are locked and unmapped, and thus they have
+ * stable content and can safely be copied to destination memory that
+ * is allocated by the drivers.
+ */
+ return 0;
+
+}
+EXPORT_SYMBOL(migrate_vma_setup);
+
static void migrate_vma_insert_page(struct migrate_vma *migrate,
unsigned long addr,
struct page *page,
@@ -2709,7 +2803,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
*src &= ~MIGRATE_PFN_MIGRATE;
}

-/*
+/**
* migrate_vma_pages() - migrate meta-data from src page to dst page
* @migrate: migrate struct containing all migration information
*
@@ -2717,7 +2811,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
* struct page. This effectively finishes the migration from source page to the
* destination page.
*/
-static void migrate_vma_pages(struct migrate_vma *migrate)
+void migrate_vma_pages(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
const unsigned long start = migrate->start;
@@ -2791,8 +2885,9 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
if (notified)
mmu_notifier_invalidate_range_only_end(&range);
}
+EXPORT_SYMBOL(migrate_vma_pages);

-/*
+/**
* migrate_vma_finalize() - restore CPU page table entry
* @migrate: migrate struct containing all migration information
*
@@ -2803,7 +2898,7 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
* This also unlocks the pages and puts them back on the lru, or drops the extra
* refcount, for device pages.
*/
-static void migrate_vma_finalize(struct migrate_vma *migrate)
+void migrate_vma_finalize(struct migrate_vma *migrate)
{
const unsigned long npages = migrate->npages;
unsigned long i;
@@ -2846,124 +2941,5 @@ static void migrate_vma_finalize(struct migrate_vma *migrate)
}
}
}
-
-/*
- * migrate_vma() - migrate a range of memory inside vma
- *
- * @ops: migration callback for allocating destination memory and copying
- * @vma: virtual memory area containing the range to be migrated
- * @start: start address of the range to migrate (inclusive)
- * @end: end address of the range to migrate (exclusive)
- * @src: array of hmm_pfn_t containing source pfns
- * @dst: array of hmm_pfn_t containing destination pfns
- * @private: pointer passed back to each of the callback
- * Returns: 0 on success, error code otherwise
- *
- * This function tries to migrate a range of memory virtual address range, using
- * callbacks to allocate and copy memory from source to destination. First it
- * collects all the pages backing each virtual address in the range, saving this
- * inside the src array. Then it locks those pages and unmaps them. Once the pages
- * are locked and unmapped, it checks whether each page is pinned or not. Pages
- * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this function)
- * in the corresponding src array entry. It then restores any pages that are
- * pinned, by remapping and unlocking those pages.
- *
- * At this point it calls the alloc_and_copy() callback. For documentation on
- * what is expected from that callback, see struct migrate_vma_ops comments in
- * include/linux/migrate.h
- *
- * After the alloc_and_copy() callback, this function goes over each entry in
- * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
- * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
- * then the function tries to migrate struct page information from the source
- * struct page to the destination struct page. If it fails to migrate the struct
- * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the src
- * array.
- *
- * At this point all successfully migrated pages have an entry in the src
- * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
- * array entry with MIGRATE_PFN_VALID flag set.
- *
- * It then calls the finalize_and_map() callback. See comments for "struct
- * migrate_vma_ops", in include/linux/migrate.h for details about
- * finalize_and_map() behavior.
- *
- * After the finalize_and_map() callback, for successfully migrated pages, this
- * function updates the CPU page table to point to new pages, otherwise it
- * restores the CPU page table to point to the original source pages.
- *
- * Function returns 0 after the above steps, even if no pages were migrated
- * (The function only returns an error if any of the arguments are invalid.)
- *
- * Both src and dst array must be big enough for (end - start) >> PAGE_SHIFT
- * unsigned long entries.
- */
-int migrate_vma(const struct migrate_vma_ops *ops,
- struct vm_area_struct *vma,
- unsigned long start,
- unsigned long end,
- unsigned long *src,
- unsigned long *dst,
- void *private)
-{
- struct migrate_vma migrate;
-
- /* Sanity check the arguments */
- start &= PAGE_MASK;
- end &= PAGE_MASK;
- if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
- vma_is_dax(vma))
- return -EINVAL;
- if (start < vma->vm_start || start >= vma->vm_end)
- return -EINVAL;
- if (end <= vma->vm_start || end > vma->vm_end)
- return -EINVAL;
- if (!ops || !src || !dst || start >= end)
- return -EINVAL;
-
- memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
- migrate.src = src;
- migrate.dst = dst;
- migrate.start = start;
- migrate.npages = 0;
- migrate.cpages = 0;
- migrate.end = end;
- migrate.vma = vma;
-
- /* Collect, and try to unmap source pages */
- migrate_vma_collect(&migrate);
- if (!migrate.cpages)
- return 0;
-
- /* Lock and isolate page */
- migrate_vma_prepare(&migrate);
- if (!migrate.cpages)
- return 0;
-
- /* Unmap pages */
- migrate_vma_unmap(&migrate);
- if (!migrate.cpages)
- return 0;
-
- /*
- * At this point pages are locked and unmapped, and thus they have
- * stable content and can safely be copied to destination memory that
- * is allocated by the callback.
- *
- * Note that migration can fail in migrate_vma_struct_page() for each
- * individual page.
- */
- ops->alloc_and_copy(vma, src, dst, start, end, private);
-
- /* This does the real migration of struct page */
- migrate_vma_pages(&migrate);
-
- ops->finalize_and_map(vma, src, dst, start, end, private);
-
- /* Unlock and remap pages */
- migrate_vma_finalize(&migrate);
-
- return 0;
-}
-EXPORT_SYMBOL(migrate_vma);
+EXPORT_SYMBOL(migrate_vma_finalize);
#endif /* defined(MIGRATE_VMA_HELPER) */
--
2.20.1
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