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Message-ID: <2cfa271b-0d40-4aaa-7c01-40c3495b01a8@linux.alibaba.com>
Date: Tue, 10 Jan 2023 18:30:48 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Huang Ying <ying.huang@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Zi Yan <ziy@...dia.com>, Yang Shi <shy828301@...il.com>,
Oscar Salvador <osalvador@...e.de>,
Matthew Wilcox <willy@...radead.org>,
Bharata B Rao <bharata@....com>,
Alistair Popple <apopple@...dia.com>,
haoxin <xhao@...ux.alibaba.com>
Subject: Re: [PATCH -v2 2/9] migrate_pages: separate hugetlb folios migration
On 1/10/2023 3:53 PM, Huang Ying wrote:
> This is a preparation patch to batch the folio unmapping and moving
> for the non-hugetlb folios. Based on that we can batch the TLB
> shootdown during the folio migration and make it possible to use some
> hardware accelerator for the folio copying.
>
> In this patch the hugetlb folios and non-hugetlb folios migration is
> separated in migrate_pages() to make it easy to change the non-hugetlb
> folios migration implementation.
>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> 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>
> Cc: Bharata B Rao <bharata@....com>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: haoxin <xhao@...ux.alibaba.com>
> ---
> mm/migrate.c | 141 +++++++++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 119 insertions(+), 22 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index d21de40861a0..04e6802c236c 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1396,6 +1396,8 @@ static inline int try_split_folio(struct folio *folio, struct list_head *split_f
> return rc;
> }
>
> +#define NR_MAX_MIGRATE_PAGES_RETRY 10
> +
> struct migrate_pages_stats {
> int nr_succeeded; /* Normal pages and THP migrated successfully, in units
> of base pages */
> @@ -1406,6 +1408,95 @@ struct migrate_pages_stats {
> int nr_thp_split; /* THP split before migrating */
> };
>
> +/*
> + * Returns the number of hugetlb folios that were not migrated, or an error code
> + * after NR_MAX_MIGRATE_PAGES_RETRY attempts or if no hugetlb folios are movable
> + * any more because the list has become empty or no retryable hugetlb folios
> + * exist any more. It is caller's responsibility to call putback_movable_pages()
> + * to return hugetlb folios to the LRU or free list only if ret != 0.
This can be confused, since we did not put the hugetlb back into any LRU
by putback_movable_pages(), right?
The code look good to me.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> + */
> +static int migrate_hugetlbs(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,
> + struct migrate_pages_stats *stats,
> + struct list_head *ret_folios)
> +{
> + int retry = 1;
> + int nr_failed = 0;
> + int nr_retry_pages = 0;
> + int pass = 0;
> + struct folio *folio, *folio2;
> + int rc, nr_pages;
> +
> + for (pass = 0; pass < NR_MAX_MIGRATE_PAGES_RETRY && retry; pass++) {
> + retry = 0;
> + nr_retry_pages = 0;
> +
> + list_for_each_entry_safe(folio, folio2, from, lru) {
> + if (!folio_test_hugetlb(folio))
> + continue;
> +
> + nr_pages = folio_nr_pages(folio);
> +
> + cond_resched();
> +
> + rc = unmap_and_move_huge_page(get_new_page,
> + put_new_page, private,
> + &folio->page, pass > 2, mode,
> + reason, ret_folios);
> + /*
> + * The rules are:
> + * Success: 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_folios list
> + */
> + switch(rc) {
> + case -ENOSYS:
> + /* Hugetlb migration is unsupported */
> + nr_failed++;
> + stats->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 folios, just exit.
> + */
> + stats->nr_failed_pages += nr_pages + nr_retry_pages;
> + return -ENOMEM;
> + case -EAGAIN:
> + retry++;
> + nr_retry_pages += nr_pages;
> + break;
> + case MIGRATEPAGE_SUCCESS:
> + stats->nr_succeeded += nr_pages;
> + break;
> + default:
> + /*
> + * Permanent failure (-EBUSY, etc.):
> + * unlike -EAGAIN case, the failed folio is
> + * removed from migration folio list and not
> + * retried in the next outer loop.
> + */
> + nr_failed++;
> + stats->nr_failed_pages += nr_pages;
> + break;
> + }
> + }
> + }
> + /*
> + * nr_failed is number of hugetlb folios failed to be migrated. After
> + * NR_MAX_MIGRATE_PAGES_RETRY attempts, give up and count retried hugetlb
> + * folios as failed.
> + */
> + nr_failed += retry;
> + stats->nr_failed_pages += nr_retry_pages;
> +
> + return nr_failed;
> +}
> +
> /*
> * migrate_pages - migrate the folios specified in a list, to the free folios
> * supplied as the target for the page migration
> @@ -1422,10 +1513,10 @@ struct migrate_pages_stats {
> * @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 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.
> + * The function returns after NR_MAX_MIGRATE_PAGES_RETRY 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 folio, large folio, hugetlb} that were not
> * migrated, or an error code. The number of large folio splits will be
> @@ -1439,7 +1530,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> int retry = 1;
> int large_retry = 1;
> int thp_retry = 1;
> - int nr_failed = 0;
> + int nr_failed;
> int nr_retry_pages = 0;
> int nr_large_failed = 0;
> int pass = 0;
> @@ -1456,38 +1547,45 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> trace_mm_migrate_pages_start(mode, reason);
>
> memset(&stats, 0, sizeof(stats));
> + rc = migrate_hugetlbs(from, get_new_page, put_new_page, private, mode, reason,
> + &stats, &ret_folios);
> + if (rc < 0)
> + goto out;
> + nr_failed = rc;
> +
> split_folio_migration:
> - for (pass = 0; pass < 10 && (retry || large_retry); pass++) {
> + for (pass = 0;
> + pass < NR_MAX_MIGRATE_PAGES_RETRY && (retry || large_retry);
> + pass++) {
> retry = 0;
> large_retry = 0;
> thp_retry = 0;
> nr_retry_pages = 0;
>
> list_for_each_entry_safe(folio, folio2, from, lru) {
> + /* Retried hugetlb folios will be kept in list */
> + if (folio_test_hugetlb(folio)) {
> + list_move_tail(&folio->lru, &ret_folios);
> + continue;
> + }
> +
> /*
> * Large folio statistics is based on the source large
> * folio. Capture required information that might get
> * lost during migration.
> */
> - is_large = folio_test_large(folio) && !folio_test_hugetlb(folio);
> + is_large = folio_test_large(folio);
> is_thp = is_large && folio_test_pmd_mappable(folio);
> nr_pages = folio_nr_pages(folio);
> +
> cond_resched();
>
> - if (folio_test_hugetlb(folio))
> - rc = unmap_and_move_huge_page(get_new_page,
> - put_new_page, private,
> - &folio->page, pass > 2, mode,
> - reason,
> - &ret_folios);
> - else
> - rc = unmap_and_move(get_new_page, put_new_page,
> - private, folio, pass > 2, mode,
> - reason, &ret_folios);
> + rc = unmap_and_move(get_new_page, put_new_page,
> + private, folio, pass > 2, mode,
> + reason, &ret_folios);
> /*
> * The rules are:
> - * Success: non hugetlb folio will be freed, hugetlb
> - * folio will be put back
> + * Success: folio will be freed
> * -EAGAIN: stay on the from list
> * -ENOMEM: stay on the from list
> * -ENOSYS: stay on the from list
> @@ -1514,7 +1612,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> stats.nr_thp_split += is_thp;
> break;
> }
> - /* Hugetlb migration is unsupported */
> } else if (!no_split_folio_counting) {
> nr_failed++;
> }
> @@ -1608,8 +1705,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> */
> if (!list_empty(&split_folios)) {
> /*
> - * Move non-migrated folios (after 10 retries) to ret_folios
> - * to avoid migrating them again.
> + * Move non-migrated folios (after NR_MAX_MIGRATE_PAGES_RETRY
> + * retries) to ret_folios to avoid migrating them again.
> */
> list_splice_init(from, &ret_folios);
> list_splice_init(&split_folios, from);
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