On 26 Dec 2022, at 19:28, Huang Ying wrote: > In this patch the _unmap and _move stage of the folio migration is > batched. That for, previously, it is, > > for each folio > _unmap() > _move() > > Now, it is, > > for each folio > _unmap() > for each folio > _move() Also worth adding some notes here, we need extra code to undo the _unmap() if _move() fails. Andrew has asked for comments on *_undo_src/dst(), but I think it would be better to provide a high level new workflow, in the form of pseudo code, in git log and the comment for migrate_pages(). The extra cleanup code for a failed _move() with a previously successful _unmap() might not be obvious to everyone. > > Based on this, we can batch the TLB flushing and use some hardware > accelerator to copy folios between batched _unmap and batched _move > stages. > > 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 | 189 ++++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 165 insertions(+), 24 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index e2383b430932..dd68c3de3da8 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1027,8 +1027,32 @@ static void __migrate_folio_extract(struct folio *dst, > dst->private = NULL; > } > > +static void migrate_folio_undo_src(struct folio *src, > + int page_was_mapped, > + struct anon_vma *anon_vma, > + struct list_head *ret) > +{ > + if (page_was_mapped) > + remove_migration_ptes(src, src, false); > + if (anon_vma) > + put_anon_vma(anon_vma); > + folio_unlock(src); > + list_move_tail(&src->lru, ret); > +} > + > +static void migrate_folio_undo_dst(struct folio *dst, > + free_page_t put_new_page, > + unsigned long private) > +{ > + folio_unlock(dst); > + if (put_new_page) > + put_new_page(&dst->page, private); > + else > + folio_put(dst); > +} > + > static int __migrate_folio_unmap(struct folio *src, struct folio *dst, > - int force, enum migrate_mode mode) > + int force, bool force_lock, enum migrate_mode mode) > { > int rc = -EAGAIN; > int page_was_mapped = 0; > @@ -1055,6 +1079,11 @@ static int __migrate_folio_unmap(struct folio *src, struct folio *dst, > if (current->flags & PF_MEMALLOC) > goto out; > > + if (!force_lock) { > + rc = -EDEADLOCK; > + goto out; > + } > + > folio_lock(src); > } > > @@ -1168,6 +1197,8 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst, > > rc = move_to_new_folio(dst, src, mode); > > + if (rc != -EAGAIN) > + list_del(&dst->lru); > /* > * When successful, push dst to LRU immediately: so that if it > * turns out to be an mlocked page, remove_migration_ptes() will > @@ -1183,6 +1214,11 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst, > lru_add_drain(); > } > > + if (rc == -EAGAIN) { > + __migrate_folio_record(dst, page_was_mapped, anon_vma); > + return rc; > + } > + > if (page_was_mapped) > remove_migration_ptes(src, > rc == MIGRATEPAGE_SUCCESS ? dst : src, false); > @@ -1223,7 +1259,7 @@ static void migrate_folio_done(struct folio *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, > + struct folio **dstp, int force, bool force_lock, > enum migrate_mode mode, enum migrate_reason reason, > struct list_head *ret) > { > @@ -1251,7 +1287,7 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page > *dstp = dst; > > dst->private = NULL; > - rc = __migrate_folio_unmap(src, dst, force, mode); > + rc = __migrate_folio_unmap(src, dst, force, force_lock, mode); > if (rc == MIGRATEPAGE_UNMAP) > return rc; > > @@ -1260,7 +1296,7 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page > * references and be restored. > */ > /* restore the folio to right list. */ > - if (rc != -EAGAIN) > + if (rc != -EAGAIN && rc != -EDEADLOCK) > list_move_tail(&src->lru, ret); > > if (put_new_page) > @@ -1299,9 +1335,8 @@ static int migrate_folio_move(free_page_t put_new_page, unsigned long private, > */ > if (rc == MIGRATEPAGE_SUCCESS) { > migrate_folio_done(src, reason); > - } else { > - if (rc != -EAGAIN) > - list_add_tail(&src->lru, ret); > + } else if (rc != -EAGAIN) { > + list_add_tail(&src->lru, ret); > > if (put_new_page) > put_new_page(&dst->page, private); > @@ -1564,7 +1599,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > enum migrate_mode mode, int reason, struct list_head *ret_folios, > struct migrate_pages_stats *stats) > { > - int retry = 1; > + int retry; > int large_retry = 1; > int thp_retry = 1; > int nr_failed = 0; > @@ -1573,13 +1608,19 @@ 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, *dst = NULL; > - int rc, nr_pages; > + struct folio *folio, *folio2, *dst = NULL, *dst2; > + int rc, rc_saved, nr_pages; > LIST_HEAD(split_folios); > + LIST_HEAD(unmap_folios); > + LIST_HEAD(dst_folios); > bool nosplit = (reason == MR_NUMA_MISPLACED); > bool no_split_folio_counting = false; > + bool force_lock; > > -split_folio_migration: > +retry: > + rc_saved = 0; > + force_lock = true; > + retry = 1; > for (pass = 0; pass < 10 && (retry || large_retry); pass++) { > retry = 0; > large_retry = 0; > @@ -1599,16 +1640,15 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > cond_resched(); > > 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); > + folio, &dst, pass > 2, force_lock, > + mode, reason, ret_folios); > /* > * The rules are: > * Success: folio will be freed > + * Unmap: folio will be put on unmap_folios list, > + * dst folio put on dst_folios list > * -EAGAIN: stay on the from list > + * -EDEADLOCK: stay on the from list > * -ENOMEM: stay on the from list > * -ENOSYS: stay on the from list > * Other errno: put on ret_folios list > @@ -1643,7 +1683,7 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > case -ENOMEM: > /* > * When memory is low, don't bother to try to migrate > - * other folios, just exit. > + * other folios, move unmapped folios, then exit. > */ > if (is_large) { > nr_large_failed++; > @@ -1682,7 +1722,14 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > /* nr_failed isn't updated for not used */ > nr_large_failed += large_retry; > stats->nr_thp_failed += thp_retry; > - goto out; > + rc_saved = rc; > + if (list_empty(&unmap_folios)) > + goto out; > + else > + goto move; > + case -EDEADLOCK: > + rc_saved = rc; > + goto move; > case -EAGAIN: > if (is_large) { > large_retry++; > @@ -1696,6 +1743,15 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > stats->nr_succeeded += nr_pages; > stats->nr_thp_succeeded += is_thp; > break; > + case MIGRATEPAGE_UNMAP: > + /* > + * We have locked some pages, don't force lock > + * to avoid deadlock. > + */ > + force_lock = false; > + list_move_tail(&folio->lru, &unmap_folios); > + list_add_tail(&dst->lru, &dst_folios); > + break; > default: > /* > * Permanent failure (-EBUSY, etc.): > @@ -1719,12 +1775,93 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > nr_large_failed += large_retry; > stats->nr_thp_failed += thp_retry; > stats->nr_failed_pages += nr_retry_pages; > +move: > + retry = 1; > + for (pass = 0; pass < 10 && (retry || large_retry); pass++) { > + retry = 0; > + large_retry = 0; > + thp_retry = 0; > + nr_retry_pages = 0; > + > + dst = list_first_entry(&dst_folios, struct folio, lru); > + dst2 = list_next_entry(dst, lru); > + list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) { > + is_large = folio_test_large(folio); > + is_thp = is_large && folio_test_pmd_mappable(folio); > + nr_pages = folio_nr_pages(folio); > + > + cond_resched(); > + > + rc = migrate_folio_move(put_new_page, private, > + folio, dst, mode, > + reason, ret_folios); > + /* > + * The rules are: > + * Success: folio will be freed > + * -EAGAIN: stay on the unmap_folios list > + * Other errno: put on ret_folios list > + */ > + switch(rc) { > + case -EAGAIN: > + if (is_large) { > + large_retry++; > + thp_retry += is_thp; > + } else if (!no_split_folio_counting) { > + retry++; > + } > + nr_retry_pages += nr_pages; > + break; > + case MIGRATEPAGE_SUCCESS: > + stats->nr_succeeded += nr_pages; > + stats->nr_thp_succeeded += is_thp; > + break; > + default: > + if (is_large) { > + nr_large_failed++; > + stats->nr_thp_failed += is_thp; > + } else if (!no_split_folio_counting) { > + nr_failed++; > + } > + > + stats->nr_failed_pages += nr_pages; > + break; > + } > + dst = dst2; > + dst2 = list_next_entry(dst, lru); > + } > + } > + nr_failed += retry; > + nr_large_failed += large_retry; > + stats->nr_thp_failed += thp_retry; > + stats->nr_failed_pages += nr_retry_pages; > + > + if (rc_saved) > + rc = rc_saved; > + else > + rc = nr_failed + nr_large_failed; > +out: > + /* Cleanup remaining folios */ > + dst = list_first_entry(&dst_folios, struct folio, lru); > + dst2 = list_next_entry(dst, lru); > + list_for_each_entry_safe(folio, folio2, &unmap_folios, lru) { > + int page_was_mapped = 0; > + struct anon_vma *anon_vma = NULL; > + > + __migrate_folio_extract(dst, &page_was_mapped, &anon_vma); > + migrate_folio_undo_src(folio, page_was_mapped, anon_vma, > + ret_folios); > + list_del(&dst->lru); > + migrate_folio_undo_dst(dst, put_new_page, private); > + dst = dst2; > + dst2 = list_next_entry(dst, lru); > + } > + > /* > * 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(&split_folios)) { > + if (rc >= 0 && !list_empty(&split_folios)) { > /* > * Move non-migrated folios (after 10 retries) to ret_folios > * to avoid migrating them again. > @@ -1732,12 +1869,16 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, > list_splice_init(from, ret_folios); > list_splice_init(&split_folios, from); > no_split_folio_counting = true; > - retry = 1; > - goto split_folio_migration; > + goto retry; > } > > - rc = nr_failed + nr_large_failed; > -out: > + /* > + * We have unlocked all locked pages, so we can force lock now, let's > + * try again. > + */ > + if (rc == -EDEADLOCK) > + goto retry; > + > return rc; > } > > -- > 2.35.1 -- Best Regards, Yan, Zi