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migrate_pages: split unmap_and_move() to _unmap() and _move()
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This is a preparation patch to batch the folio unmapping and moving.

In this patch, unmap_and_move() is split to migrate_folio_unmap() and
migrate_folio_move().  So, we can batch _unmap() and _move() in different
loops later.  To pass some information between unmap and move, the
original unused dst->mapping and dst->private are used.

Link: https://lkml.kernel.org/r/20230213123444.155149-5-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@yhuang-intel @akpm00
yhuang-intel authored and akpm00 committed Feb 17, 2023
1 parent 42012e0 commit 64c8902
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Showing 2 changed files with 129 additions and 41 deletions.
1 change: 1 addition & 0 deletions include/linux/migrate.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ struct migration_target_control;
* - zero on page migration success;
*/
#define MIGRATEPAGE_SUCCESS 0
#define MIGRATEPAGE_UNMAP 1

/**
* struct movable_operations - Driver page migration
Expand Down
169 changes: 128 additions & 41 deletions mm/migrate.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1027,11 +1027,53 @@ static int move_to_new_folio(struct folio *dst, struct folio *src,
return rc;
}

static int __unmap_and_move(struct folio *src, struct folio *dst,
/*
* To record some information during migration, we use some unused
* fields (mapping and private) of struct folio of the newly allocated
* destination folio. This is safe because nobody is using them
* except us.
*/
static void __migrate_folio_record(struct folio *dst,
unsigned long page_was_mapped,
struct anon_vma *anon_vma)
{
dst->mapping = (void *)anon_vma;
dst->private = (void *)page_was_mapped;
}

static void __migrate_folio_extract(struct folio *dst,
int *page_was_mappedp,
struct anon_vma **anon_vmap)
{
*anon_vmap = (void *)dst->mapping;
*page_was_mappedp = (unsigned long)dst->private;
dst->mapping = NULL;
dst->private = NULL;
}

/* Cleanup src folio upon migration success */
static void migrate_folio_done(struct folio *src,
enum migrate_reason reason)
{
/*
* Compaction can migrate also non-LRU pages which are
* not accounted to NR_ISOLATED_*. They can be recognized
* as __PageMovable
*/
if (likely(!__folio_test_movable(src)))
mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
folio_is_file_lru(src), -folio_nr_pages(src));

if (reason != MR_MEMORY_FAILURE)
/* We release the page in page_handle_poison. */
folio_put(src);
}

static int __migrate_folio_unmap(struct folio *src, struct folio *dst,
int force, enum migrate_mode mode)
{
int rc = -EAGAIN;
bool page_was_mapped = false;
int page_was_mapped = 0;
struct anon_vma *anon_vma = NULL;
bool is_lru = !__PageMovable(&src->page);

Expand Down Expand Up @@ -1107,8 +1149,8 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
goto out_unlock;

if (unlikely(!is_lru)) {
rc = move_to_new_folio(dst, src, mode);
goto out_unlock_both;
__migrate_folio_record(dst, page_was_mapped, anon_vma);
return MIGRATEPAGE_UNMAP;
}

/*
Expand All @@ -1133,11 +1175,42 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
VM_BUG_ON_FOLIO(folio_test_anon(src) &&
!folio_test_ksm(src) && !anon_vma, src);
try_to_migrate(src, 0);
page_was_mapped = true;
page_was_mapped = 1;
}

if (!folio_mapped(src))
rc = move_to_new_folio(dst, src, mode);
if (!folio_mapped(src)) {
__migrate_folio_record(dst, page_was_mapped, anon_vma);
return MIGRATEPAGE_UNMAP;
}

if (page_was_mapped)
remove_migration_ptes(src, src, false);

out_unlock_both:
folio_unlock(dst);
out_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);
folio_unlock(src);
out:

return rc;
}

static int __migrate_folio_move(struct folio *src, struct folio *dst,
enum migrate_mode mode)
{
int rc;
int page_was_mapped = 0;
struct anon_vma *anon_vma = NULL;
bool is_lru = !__PageMovable(&src->page);

__migrate_folio_extract(dst, &page_was_mapped, &anon_vma);

rc = move_to_new_folio(dst, src, mode);
if (unlikely(!is_lru))
goto out_unlock_both;

/*
* When successful, push dst to LRU immediately: so that if it
Expand All @@ -1160,12 +1233,10 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,

out_unlock_both:
folio_unlock(dst);
out_unlock:
/* Drop an anon_vma reference if we took one */
if (anon_vma)
put_anon_vma(anon_vma);
folio_unlock(src);
out:
/*
* If migration is successful, decrease refcount of dst,
* which will not free the page because new page owner increased
Expand All @@ -1177,19 +1248,15 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
return rc;
}

/*
* Obtain the lock on folio, remove all ptes and migrate the folio
* to the newly allocated folio in dst.
*/
static int unmap_and_move(new_page_t get_new_page,
free_page_t put_new_page,
unsigned long private, struct folio *src,
int force, enum migrate_mode mode,
enum migrate_reason reason,
struct list_head *ret)
/* Obtain the lock on page, remove all ptes. */
static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page,
unsigned long private, struct folio *src,
struct folio **dstp, int force,
enum migrate_mode mode, enum migrate_reason reason,
struct list_head *ret)
{
struct folio *dst;
int rc = MIGRATEPAGE_SUCCESS;
int rc = MIGRATEPAGE_UNMAP;
struct page *newpage = NULL;

if (!thp_migration_supported() && folio_test_transhuge(src))
Expand All @@ -1200,20 +1267,49 @@ static int unmap_and_move(new_page_t get_new_page,
folio_clear_active(src);
folio_clear_unevictable(src);
/* free_pages_prepare() will clear PG_isolated. */
goto out;
list_del(&src->lru);
migrate_folio_done(src, reason);
return MIGRATEPAGE_SUCCESS;
}

newpage = get_new_page(&src->page, private);
if (!newpage)
return -ENOMEM;
dst = page_folio(newpage);
*dstp = dst;

dst->private = NULL;
rc = __unmap_and_move(src, dst, force, mode);
rc = __migrate_folio_unmap(src, dst, force, mode);
if (rc == MIGRATEPAGE_UNMAP)
return rc;

/*
* A folio that has not been unmapped will be restored to
* right list unless we want to retry.
*/
if (rc != -EAGAIN)
list_move_tail(&src->lru, ret);

if (put_new_page)
put_new_page(&dst->page, private);
else
folio_put(dst);

return rc;
}

/* Migrate the folio to the newly allocated folio in dst. */
static int migrate_folio_move(free_page_t put_new_page, unsigned long private,
struct folio *src, struct folio *dst,
enum migrate_mode mode, enum migrate_reason reason,
struct list_head *ret)
{
int rc;

rc = __migrate_folio_move(src, dst, mode);
if (rc == MIGRATEPAGE_SUCCESS)
set_page_owner_migrate_reason(&dst->page, reason);

out:
if (rc != -EAGAIN) {
/*
* A folio that has been migrated has all references
Expand All @@ -1229,20 +1325,7 @@ static int unmap_and_move(new_page_t get_new_page,
* we want to retry.
*/
if (rc == MIGRATEPAGE_SUCCESS) {
/*
* Compaction can migrate also non-LRU folios which are
* not accounted to NR_ISOLATED_*. They can be recognized
* as __folio_test_movable
*/
if (likely(!__folio_test_movable(src)))
mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
folio_is_file_lru(src), -folio_nr_pages(src));

if (reason != MR_MEMORY_FAILURE)
/*
* We release the folio in page_handle_poison.
*/
folio_put(src);
migrate_folio_done(src, reason);
} else {
if (rc != -EAGAIN)
list_add_tail(&src->lru, ret);
Expand Down Expand Up @@ -1534,7 +1617,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,
int pass = 0;
bool is_large = false;
bool is_thp = false;
struct folio *folio, *folio2;
struct folio *folio, *folio2, *dst = NULL;
int rc, nr_pages;
LIST_HEAD(split_folios);
bool nosplit = (reason == MR_NUMA_MISPLACED);
Expand All @@ -1561,9 +1644,13 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page,

cond_resched();

rc = unmap_and_move(get_new_page, put_new_page,
private, folio, pass > 2, mode,
reason, ret_folios);
rc = migrate_folio_unmap(get_new_page, put_new_page, private,
folio, &dst, pass > 2, mode,
reason, ret_folios);
if (rc == MIGRATEPAGE_UNMAP)
rc = migrate_folio_move(put_new_page, private,
folio, dst, mode,
reason, ret_folios);
/*
* The rules are:
* Success: folio will be freed
Expand Down

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