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SubjectRe: [PATCH 4/8] migrate_pages: split unmap_and_move() to _unmap() and _move()
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On 26 Dec 2022, at 19:28, Huang Ying wrote:

> 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.
>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.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: haoxin <xhao@linux.alibaba.com>
> ---
> include/linux/migrate.h | 1 +
> mm/migrate.c | 162 +++++++++++++++++++++++++++++-----------
> 2 files changed, 121 insertions(+), 42 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 3ef77f52a4f0..7376074f2e1e 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -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
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 97ea0737ab2b..e2383b430932 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1009,11 +1009,29 @@ 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,
> +static void __migrate_folio_record(struct folio *dst,
> + unsigned long page_was_mapped,
> + struct anon_vma *anon_vma)
> +{
> + dst->mapping = (struct address_space *)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 = (struct anon_vma *)dst->mapping;
> + *page_was_mappedp = (unsigned long)dst->private;
> + dst->mapping = NULL;
> + dst->private = NULL;
> +}
> +

We probably need comments on these two functions on using dst->mapping
and dst->private. It might be hard to get the behavior later by
digging into the git log and/or looking at the code.

> +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);
>
> @@ -1089,8 +1107,8 @@ 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;
> }
>
> /*
> @@ -1115,11 +1133,40 @@ 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;
> +
> + __migrate_folio_extract(dst, &page_was_mapped, &anon_vma);
> +
> + rc = move_to_new_folio(dst, src, mode);
>
> /*
> * When successful, push dst to LRU immediately: so that if it
> @@ -1140,14 +1187,11 @@ static int __unmap_and_move(struct folio *src, struct folio *dst,
> remove_migration_ptes(src,
> rc == MIGRATEPAGE_SUCCESS ? dst : 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:
> /*
> * If migration is successful, decrease refcount of dst,
> * which will not free the page because new page owner increased
> @@ -1159,19 +1203,32 @@ 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)
> +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);
> +}
> +
> +/* 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))
> @@ -1182,20 +1239,50 @@ 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 page that has not been migrated will have kept its
> + * references and be restored.
> + */
> + /* restore the folio to right list. */
> + 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
> @@ -1211,20 +1298,7 @@ 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);
> @@ -1499,7 +1573,7 @@ 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);
> @@ -1524,9 +1598,13 @@ 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
> --
> 2.35.1


--
Best Regards,
Yan, Zi
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