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Date: Mon, 7 Nov 2022 16:13:54 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Huang Ying <ying.huang@...el.com>, linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
Oscar Salvador <osalvador@...e.de>,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 2/2] migrate: convert migrate_pages() to use folios
On 11/4/2022 4:30 PM, Huang Ying wrote:
> Quite straightforward, the page functions are converted to
> corresponding folio functions. Same for comments.
>
> THP specific code are converted to be large folio.
>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Yang Shi <shy828301@...il.com>
> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Matthew Wilcox <willy@...radead.org>
> ---
> mm/migrate.c | 201 +++++++++++++++++++++++++++------------------------
> 1 file changed, 107 insertions(+), 94 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f6dd749dd2f8..b41289ef3b65 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1373,218 +1373,231 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
> return rc;
> }
>
> -static inline int try_split_thp(struct page *page, struct list_head *split_pages)
> +static inline int try_split_folio(struct folio *folio, struct list_head *split_folios)
> {
> int rc;
>
> - lock_page(page);
> - rc = split_huge_page_to_list(page, split_pages);
> - unlock_page(page);
> + folio_lock(folio);
> + rc = split_folio_to_list(folio, split_folios);
> + folio_unlock(folio);
> if (!rc)
> - list_move_tail(&page->lru, split_pages);
> + list_move_tail(&folio->lru, split_folios);
>
> return rc;
> }
>
> /*
> - * migrate_pages - migrate the pages specified in a list, to the free pages
> + * migrate_pages - migrate the folios specified in a list, to the free folios
> * supplied as the target for the page migration
> *
> - * @from: The list of pages to be migrated.
> - * @get_new_page: The function used to allocate free pages to be used
> - * as the target of the page migration.
> - * @put_new_page: The function used to free target pages if migration
> + * @from: The list of folios to be migrated.
> + * @get_new_page: The function used to allocate free folios to be used
> + * as the target of the folio migration.
> + * @put_new_page: The function used to free target folios if migration
> * fails, or NULL if no special handling is necessary.
> * @private: Private data to be passed on to get_new_page()
> * @mode: The migration mode that specifies the constraints for
> - * page migration, if any.
> - * @reason: The reason for page migration.
> - * @ret_succeeded: Set to the number of normal pages migrated successfully if
> + * folio migration, if any.
> + * @reason: The reason for folio migration.
> + * @ret_succeeded: Set to the number of folios migrated successfully if
> * the caller passes a non-NULL pointer.
> *
> - * The function returns after 10 attempts or if no pages are movable any more
> - * because the list has become empty or no retryable pages exist any more.
> - * It is caller's responsibility to call putback_movable_pages() to return pages
> + * The function returns after 10 attempts or if no folios are movable any more
> + * because the list has become empty or no retryable folios exist any more.
> + * It is caller's responsibility to call putback_movable_pages() to return folios
> * to the LRU or free list only if ret != 0.
> *
> - * Returns the number of {normal page, THP, hugetlb} that were not migrated, or
> - * an error code. The number of THP splits will be considered as the number of
> - * non-migrated THP, no matter how many subpages of the THP are migrated successfully.
> + * Returns the number of {normal folio, large folio, hugetlb} that were not
> + * migrated, or an error code. The number of large folio splits will be
> + * considered as the number of non-migrated large folio, no matter how many
> + * split folios of the large folio are migrated successfully.
> */
> int migrate_pages(struct list_head *from, new_page_t get_new_page,
> free_page_t put_new_page, unsigned long private,
> enum migrate_mode mode, int reason, unsigned int *ret_succeeded)
> {
> int retry = 1;
> + int large_retry = 1;
> int thp_retry = 1;
> int nr_failed = 0;
> int nr_failed_pages = 0;
> int nr_retry_pages = 0;
> int nr_succeeded = 0;
> int nr_thp_succeeded = 0;
> + int nr_large_failed = 0;
> int nr_thp_failed = 0;
> int nr_thp_split = 0;
> int pass = 0;
> + bool is_large = false;
> bool is_thp = false;
> - struct page *page;
> - struct page *page2;
> - int rc, nr_subpages;
> - LIST_HEAD(ret_pages);
> - LIST_HEAD(thp_split_pages);
> + struct folio *folio, *folio2;
> + int rc, nr_pages;
> + LIST_HEAD(ret_folios);
> + LIST_HEAD(split_folios);
> bool nosplit = (reason == MR_NUMA_MISPLACED);
> - bool no_subpage_counting = false;
> + bool no_split_folio_counting = false;
>
> trace_mm_migrate_pages_start(mode, reason);
>
> -thp_subpage_migration:
> - for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
> +split_folio_migration:
> + for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
> retry = 0;
> + large_retry = 0;
> thp_retry = 0;
> nr_retry_pages = 0;
>
> - list_for_each_entry_safe(page, page2, from, lru) {
> + list_for_each_entry_safe(folio, folio2, from, lru) {
> /*
> - * THP statistics is based on the source huge page.
> - * Capture required information that might get lost
> - * during migration.
> + * large folio statistics is based on the source large
Nit: s/large/Large
> + * folio. Capture required information that might get
> + * lost during migration.
> */
> - is_thp = PageTransHuge(page) && !PageHuge(page);
> - nr_subpages = compound_nr(page);
> + is_large = folio_test_large(folio) && !folio_test_hugetlb(folio);
> + is_thp = is_large && folio_test_pmd_mappable(folio);
> + nr_pages = folio_nr_pages(folio);
> cond_resched();
>
> - if (PageHuge(page))
> + if (folio_test_hugetlb(folio))
> rc = unmap_and_move_huge_page(get_new_page,
> - put_new_page, private, page,
> - pass > 2, mode, reason,
> - &ret_pages);
> + put_new_page, private,
> + &folio->page, pass > 2, mode,
> + reason,
> + &ret_folios);
> else
> rc = unmap_and_move(get_new_page, put_new_page,
> - private, page_folio(page), pass > 2, mode,
> - reason, &ret_pages);
> + private, folio, pass > 2, mode,
> + reason, &ret_folios);
> /*
> * The rules are:
> - * Success: non hugetlb page will be freed, hugetlb
> - * page will be put back
> + * Success: non hugetlb folio will be freed, hugetlb
> + * folio will be put back
> * -EAGAIN: stay on the from list
> * -ENOMEM: stay on the from list
> * -ENOSYS: stay on the from list
> - * Other errno: put on ret_pages list then splice to
> + * Other errno: put on ret_folios list then splice to
> * from list
> */
> switch(rc) {
> /*
> - * THP migration might be unsupported or the
> - * allocation could've failed so we should
> - * retry on the same page with the THP split
> - * to base pages.
> + * Large folio migration might be unsupported or
> + * the allocation could've failed so we should retry
> + * on the same folio with the large folio split
> + * to normal folios.
> *
> - * Sub-pages are put in thp_split_pages, and
> + * Split folios are put in split_folios, and
> * we will migrate them after the rest of the
> * list is processed.
> */
> case -ENOSYS:
> - /* THP migration is unsupported */
> - if (is_thp) {
> - nr_thp_failed++;
> - if (!try_split_thp(page, &thp_split_pages)) {
> - nr_thp_split++;
> + /* Large folio migration is unsupported */
> + if (is_large) {
> + nr_large_failed++;
> + nr_thp_failed += is_thp;
> + if (!try_split_folio(folio, &split_folios)) {
> + nr_thp_split += is_thp;
> break;
> }
> /* Hugetlb migration is unsupported */
> - } else if (!no_subpage_counting) {
> + } else if (!no_split_folio_counting) {
> nr_failed++;
> }
>
> - nr_failed_pages += nr_subpages;
> - list_move_tail(&page->lru, &ret_pages);
> + nr_failed_pages += nr_pages;
> + list_move_tail(&folio->lru, &ret_folios);
> break;
> case -ENOMEM:
> /*
> * When memory is low, don't bother to try to migrate
> - * other pages, just exit.
> + * other folios, just exit.
> */
> - if (is_thp) {
> - nr_thp_failed++;
> - /* THP NUMA faulting doesn't split THP to retry. */
> - if (!nosplit && !try_split_thp(page, &thp_split_pages)) {
> - nr_thp_split++;
> + if (is_large) {
> + nr_large_failed++;
> + nr_thp_failed += is_thp;
> + /* Large folio NUMA faulting doesn't split to retry. */
> + if (!nosplit && !try_split_folio(folio, &split_folios)) {
I am not sure if need to add a is_thp validation before calling
try_split_folio()?
BTW, you should rebase on the mm-unstable branch, since I've added a
retry for THP split.
> + nr_thp_split += is_thp;
> break;
> }
> - } else if (!no_subpage_counting) {
> + } else if (!no_split_folio_counting) {
> nr_failed++;
> }
>
> - nr_failed_pages += nr_subpages + nr_retry_pages;
> + nr_failed_pages += nr_pages + nr_retry_pages;
> /*
> - * There might be some subpages of fail-to-migrate THPs
> - * left in thp_split_pages list. Move them back to migration
> + * There might be some split folios of fail-to-migrate large
> + * folios left in split_folios list. Move them back to migration
> * list so that they could be put back to the right list by
> - * the caller otherwise the page refcnt will be leaked.
> + * the caller otherwise the folio refcnt will be leaked.
> */
> - list_splice_init(&thp_split_pages, from);
> + list_splice_init(&split_folios, from);
> /* nr_failed isn't updated for not used */
> + nr_large_failed += large_retry;
> nr_thp_failed += thp_retry;
> goto out;
> case -EAGAIN:
> - if (is_thp)
> - thp_retry++;
> - else if (!no_subpage_counting)
> + if (is_large) {
> + large_retry++;
> + thp_retry += is_thp;
> + } else if (!no_split_folio_counting) {
> retry++;
> - nr_retry_pages += nr_subpages;
> + }
> + nr_retry_pages += nr_pages;
> break;
> case MIGRATEPAGE_SUCCESS:
> - nr_succeeded += nr_subpages;
> - if (is_thp)
> - nr_thp_succeeded++;
> + nr_succeeded += nr_pages;
> + nr_thp_succeeded += is_thp;
> break;
> default:
> /*
> * Permanent failure (-EBUSY, etc.):
> - * unlike -EAGAIN case, the failed page is
> - * removed from migration page list and not
> + * unlike -EAGAIN case, the failed folio is
> + * removed from migration folio list and not
> * retried in the next outer loop.
> */
> - if (is_thp)
> - nr_thp_failed++;
> - else if (!no_subpage_counting)
> + if (is_large) {
> + nr_large_failed++;
> + nr_thp_failed += is_thp;
> + } else if (!no_split_folio_counting) {
> nr_failed++;
> + }
>
> - nr_failed_pages += nr_subpages;
> + nr_failed_pages += nr_pages;
> break;
> }
> }
> }
> nr_failed += retry;
> + nr_large_failed += large_retry;
> nr_thp_failed += thp_retry;
> nr_failed_pages += nr_retry_pages;
> /*
> - * Try to migrate subpages of fail-to-migrate THPs, no nr_failed
> - * counting in this round, since all subpages of a THP is counted
> - * as 1 failure in the first round.
> + * Try to migrate split folios of fail-to-migrate large folios, no
> + * nr_failed counting in this round, since all split folios of a
> + * large folio is counted as 1 failure in the first round.
> */
> - if (!list_empty(&thp_split_pages)) {
> + if (!list_empty(&split_folios)) {
> /*
> - * Move non-migrated pages (after 10 retries) to ret_pages
> + * Move non-migrated folios (after 10 retries) to ret_folios
> * to avoid migrating them again.
> */
> - list_splice_init(from, &ret_pages);
> - list_splice_init(&thp_split_pages, from);
> - no_subpage_counting = true;
> + list_splice_init(from, &ret_folios);
> + list_splice_init(&split_folios, from);
> + no_split_folio_counting = true;
> retry = 1;
> - goto thp_subpage_migration;
> + goto split_folio_migration;
> }
>
> - rc = nr_failed + nr_thp_failed;
> + rc = nr_failed + nr_large_failed;
> out:
> /*
> - * Put the permanent failure page back to migration list, they
> + * Put the permanent failure folio back to migration list, they
> * will be put back to the right list by the caller.
> */
> - list_splice(&ret_pages, from);
> + list_splice(&ret_folios, from);
>
> /*
> - * Return 0 in case all subpages of fail-to-migrate THPs are
> - * migrated successfully.
> + * Return 0 in case all split folios of fail-to-migrate large folios
> + * are migrated successfully.
> */
> if (list_empty(from))
> rc = 0;
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