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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH -v2 2/9] migrate_pages: separate hugetlb folios migration To: Huang Ying , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zi Yan , Yang Shi , Oscar Salvador , Matthew Wilcox , Bharata B Rao , Alistair Popple , haoxin References: <20230110075327.590514-1-ying.huang@intel.com> <20230110075327.590514-3-ying.huang@intel.com> From: Baolin Wang In-Reply-To: <20230110075327.590514-3-ying.huang@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: D4F18140010 X-Rspamd-Server: rspam01 X-Stat-Signature: 9wojqxd3sauqrasucsfa8q4wkn4d4mj3 X-HE-Tag: 1673346628-237587 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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" > Cc: Zi Yan > Cc: Yang Shi > Cc: Baolin Wang > Cc: Oscar Salvador > Cc: Matthew Wilcox > Cc: Bharata B Rao > Cc: Alistair Popple > Cc: haoxin > --- > 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 > + */ > +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);