On 3 Nov 2020, at 8:03, Yang Shi wrote: > When unmap_and_move{_huge_page}() returns !-EAGAIN and !MIGRATEPAGE_SUCCESS, > the page would be put back to LRU or proper list if it is non-LRU movable > page. But, the callers always call putback_movable_pages() to put the > failed pages back later on, so it seems not very efficient to put every > single page back immediately, and the code looks convoluted. > > Put the failed page on a separate list, then splice the list to migrate > list when all pages are tried. It is the caller's responsibility to > call putback_movable_pages() to handle failures. This also makes the > code simpler and more readable. > > After the change the rules are: > * Success: non hugetlb page will be freed, hugetlb page will be put > back > * -EAGAIN: stay on the from list > * -ENOMEM: stay on the from list > * Other errno: put on ret_pages list then splice to from list Can you put this before the switch case in the migrate_pages? That will be very helpful to understand the code. > > The from list would be empty iff all pages are migrated successfully, it s/iff/if unless you really mean if and only if. :) Everything else looks good to me. Thanks for making the code cleaner. With the changes above, you can add Reviewed-by: Zi Yan . > was not so before. This has no impact to current existing callsites. > > Signed-off-by: Yang Shi > --- > mm/migrate.c | 58 ++++++++++++++++++++++++++-------------------------- > 1 file changed, 29 insertions(+), 29 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 8a2e7e19e27b..c33c92495ead 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1169,7 +1169,8 @@ static int unmap_and_move(new_page_t get_new_page, > free_page_t put_new_page, > unsigned long private, struct page *page, > int force, enum migrate_mode mode, > - enum migrate_reason reason) > + enum migrate_reason reason, > + struct list_head *ret) > { > int rc = MIGRATEPAGE_SUCCESS; > struct page *newpage = NULL; > @@ -1206,7 +1207,14 @@ static int unmap_and_move(new_page_t get_new_page, > * migrated will have kept its references and be restored. > */ > list_del(&page->lru); > + } > > + /* > + * If migration is successful, releases reference grabbed during > + * isolation. Otherwise, restore the page to right list unless > + * we want to retry. > + */ > + if (rc == MIGRATEPAGE_SUCCESS) { > /* > * Compaction can migrate also non-LRU pages which are > * not accounted to NR_ISOLATED_*. They can be recognized > @@ -1215,35 +1223,16 @@ static int unmap_and_move(new_page_t get_new_page, > if (likely(!__PageMovable(page))) > mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + > page_is_file_lru(page), -thp_nr_pages(page)); > - } > > - /* > - * If migration is successful, releases reference grabbed during > - * isolation. Otherwise, restore the page to right list unless > - * we want to retry. > - */ > - if (rc == MIGRATEPAGE_SUCCESS) { > if (reason != MR_MEMORY_FAILURE) > /* > * We release the page in page_handle_poison. > */ > put_page(page); > } else { > - if (rc != -EAGAIN) { > - if (likely(!__PageMovable(page))) { > - putback_lru_page(page); > - goto put_new; > - } > + if (rc != -EAGAIN) > + list_add_tail(&page->lru, ret); > > - lock_page(page); > - if (PageMovable(page)) > - putback_movable_page(page); > - else > - __ClearPageIsolated(page); > - unlock_page(page); > - put_page(page); > - } > -put_new: > if (put_new_page) > put_new_page(newpage, private); > else > @@ -1274,7 +1263,8 @@ static int unmap_and_move(new_page_t get_new_page, > static int unmap_and_move_huge_page(new_page_t get_new_page, > free_page_t put_new_page, unsigned long private, > struct page *hpage, int force, > - enum migrate_mode mode, int reason) > + enum migrate_mode mode, int reason, > + struct list_head *ret) > { > int rc = -EAGAIN; > int page_was_mapped = 0; > @@ -1290,7 +1280,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, > * kicking migration. > */ > if (!hugepage_migration_supported(page_hstate(hpage))) { > - putback_active_hugepage(hpage); > + list_move_tail(&hpage->lru, ret); > return -ENOSYS; > } > > @@ -1372,8 +1362,10 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, > out_unlock: > unlock_page(hpage); > out: > - if (rc != -EAGAIN) > + if (rc == MIGRATEPAGE_SUCCESS) > putback_active_hugepage(hpage); > + else if (rc != -EAGAIN && rc != MIGRATEPAGE_SUCCESS) > + list_move_tail(&hpage->lru, ret); > > /* > * If migration was not successful and there's a freeing callback, use > @@ -1404,8 +1396,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, > * > * 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. > - * The caller should call putback_movable_pages() to return pages to the LRU > - * or free list only if ret != 0. > + * It is caller's responsibility to call putback_movable_pages() to return pages > + * to the LRU or free list only if ret != 0. > * > * Returns the number of pages that were not migrated, or an error code. > */ > @@ -1426,6 +1418,7 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > struct page *page2; > int swapwrite = current->flags & PF_SWAPWRITE; > int rc, nr_subpages; > + LIST_HEAD(ret_pages); > > if (!swapwrite) > current->flags |= PF_SWAPWRITE; > @@ -1448,11 +1441,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > if (PageHuge(page)) > rc = unmap_and_move_huge_page(get_new_page, > put_new_page, private, page, > - pass > 2, mode, reason); > + pass > 2, mode, reason, > + &ret_pages); > else > rc = unmap_and_move(get_new_page, put_new_page, > private, page, pass > 2, mode, > - reason); > + reason, &ret_pages); > > switch(rc) { > case -ENOMEM: > @@ -1519,6 +1513,12 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page, > nr_thp_failed += thp_retry; > rc = nr_failed; > out: > + /* > + * Put the permanent failure page back to migration list, they > + * will be put back to the right list by the caller. > + */ > + list_splice(&ret_pages, from); > + > count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded); > count_vm_events(PGMIGRATE_FAIL, nr_failed); > count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded); > -- > 2.26.2 — Best Regards, Yan Zi