[RFC PATCH 14/25] exchange pages: concurrent exchange pages.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

It unmaps two lists of pages, then exchange them in
exchange_page_lists_mthread(), and finally remaps both lists of
pages.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 include/linux/exchange.h |   2 +
 mm/exchange.c            | 397 +++++++++++++++++++++++++++++++++++++++++++++++
 mm/exchange_page.c       |   1 -
 3 files changed, 399 insertions(+), 1 deletion(-)

diff --git a/include/linux/exchange.h b/include/linux/exchange.h
index 778068e..20d2184 100644
--- a/include/linux/exchange.h
+++ b/include/linux/exchange.h
@@ -20,4 +20,6 @@ struct exchange_page_info {
 int exchange_pages(struct list_head *exchange_list,
 			enum migrate_mode mode,
 			int reason);
+int exchange_pages_concur(struct list_head *exchange_list,
+		enum migrate_mode mode, int reason);
 #endif /* _LINUX_EXCHANGE_H */
diff --git a/mm/exchange.c b/mm/exchange.c
index ce2c899..bbada58 100644
--- a/mm/exchange.c
+++ b/mm/exchange.c
@@ -600,3 +600,400 @@ int exchange_pages(struct list_head *exchange_list,
 	}
 	return failed;
 }
+
+
+static int unmap_pair_pages_concur(struct exchange_page_info *one_pair,
+				int force, enum migrate_mode mode)
+{
+	int rc = -EAGAIN;
+	struct anon_vma *anon_vma_from_page = NULL, *anon_vma_to_page = NULL;
+	struct page *from_page = one_pair->from_page;
+	struct page *to_page = one_pair->to_page;
+
+	/* from_page lock down  */
+	if (!trylock_page(from_page)) {
+		if (!force || ((mode & MIGRATE_MODE_MASK) == MIGRATE_ASYNC))
+			goto out;
+
+		lock_page(from_page);
+	}
+
+	BUG_ON(PageWriteback(from_page));
+
+	/*
+	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
+	 * we cannot notice that anon_vma is freed while we migrates a page.
+	 * This get_anon_vma() delays freeing anon_vma pointer until the end
+	 * of migration. File cache pages are no problem because of page_lock()
+	 * File Caches may use write_page() or lock_page() in migration, then,
+	 * just care Anon page here.
+	 *
+	 * Only page_get_anon_vma() understands the subtleties of
+	 * getting a hold on an anon_vma from outside one of its mms.
+	 * But if we cannot get anon_vma, then we won't need it anyway,
+	 * because that implies that the anon page is no longer mapped
+	 * (and cannot be remapped so long as we hold the page lock).
+	 */
+	if (PageAnon(from_page) && !PageKsm(from_page))
+		one_pair->from_anon_vma = anon_vma_from_page
+					= page_get_anon_vma(from_page);
+
+	/* to_page lock down  */
+	if (!trylock_page(to_page)) {
+		if (!force || ((mode & MIGRATE_MODE_MASK) == MIGRATE_ASYNC))
+			goto out_unlock;
+
+		lock_page(to_page);
+	}
+
+	BUG_ON(PageWriteback(to_page));
+
+	/*
+	 * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
+	 * we cannot notice that anon_vma is freed while we migrates a page.
+	 * This get_anon_vma() delays freeing anon_vma pointer until the end
+	 * of migration. File cache pages are no problem because of page_lock()
+	 * File Caches may use write_page() or lock_page() in migration, then,
+	 * just care Anon page here.
+	 *
+	 * Only page_get_anon_vma() understands the subtleties of
+	 * getting a hold on an anon_vma from outside one of its mms.
+	 * But if we cannot get anon_vma, then we won't need it anyway,
+	 * because that implies that the anon page is no longer mapped
+	 * (and cannot be remapped so long as we hold the page lock).
+	 */
+	if (PageAnon(to_page) && !PageKsm(to_page))
+		one_pair->to_anon_vma = anon_vma_to_page = page_get_anon_vma(to_page);
+
+	/*
+	 * Corner case handling:
+	 * 1. When a new swap-cache page is read into, it is added to the LRU
+	 * and treated as swapcache but it has no rmap yet.
+	 * Calling try_to_unmap() against a page->mapping==NULL page will
+	 * trigger a BUG.  So handle it here.
+	 * 2. An orphaned page (see truncate_complete_page) might have
+	 * fs-private metadata. The page can be picked up due to memory
+	 * offlining.  Everywhere else except page reclaim, the page is
+	 * invisible to the vm, so the page can not be migrated.  So try to
+	 * free the metadata, so the page can be freed.
+	 */
+	if (!from_page->mapping) {
+		VM_BUG_ON_PAGE(PageAnon(from_page), from_page);
+		if (page_has_private(from_page)) {
+			try_to_free_buffers(from_page);
+			goto out_unlock_both;
+		}
+	} else if (page_mapped(from_page)) {
+		/* Establish migration ptes */
+		VM_BUG_ON_PAGE(PageAnon(from_page) && !PageKsm(from_page) &&
+					   !anon_vma_from_page, from_page);
+		try_to_unmap(from_page,
+			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+
+		one_pair->from_page_was_mapped = 1;
+	}
+
+	if (!to_page->mapping) {
+		VM_BUG_ON_PAGE(PageAnon(to_page), to_page);
+		if (page_has_private(to_page)) {
+			try_to_free_buffers(to_page);
+			goto out_unlock_both;
+		}
+	} else if (page_mapped(to_page)) {
+		/* Establish migration ptes */
+		VM_BUG_ON_PAGE(PageAnon(to_page) && !PageKsm(to_page) &&
+					   !anon_vma_to_page, to_page);
+		try_to_unmap(to_page,
+			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+
+		one_pair->to_page_was_mapped = 1;
+	}
+
+	return MIGRATEPAGE_SUCCESS;
+
+out_unlock_both:
+	if (anon_vma_to_page)
+		put_anon_vma(anon_vma_to_page);
+	unlock_page(to_page);
+out_unlock:
+	/* Drop an anon_vma reference if we took one */
+	if (anon_vma_from_page)
+		put_anon_vma(anon_vma_from_page);
+	unlock_page(from_page);
+out:
+
+	return rc;
+}
+
+static int exchange_page_mapping_concur(struct list_head *unmapped_list_ptr,
+					   struct list_head *exchange_list_ptr,
+						enum migrate_mode mode)
+{
+	int rc = -EBUSY;
+	int nr_failed = 0;
+	struct address_space *to_page_mapping, *from_page_mapping;
+	struct exchange_page_info *one_pair, *one_pair2;
+
+	list_for_each_entry_safe(one_pair, one_pair2, unmapped_list_ptr, list) {
+		struct page *from_page = one_pair->from_page;
+		struct page *to_page = one_pair->to_page;
+
+		VM_BUG_ON_PAGE(!PageLocked(from_page), from_page);
+		VM_BUG_ON_PAGE(!PageLocked(to_page), to_page);
+
+		/* copy page->mapping not use page_mapping()  */
+		to_page_mapping = page_mapping(to_page);
+		from_page_mapping = page_mapping(from_page);
+
+		BUG_ON(from_page_mapping);
+		BUG_ON(to_page_mapping);
+
+		BUG_ON(PageWriteback(from_page));
+		BUG_ON(PageWriteback(to_page));
+
+		/* actual page mapping exchange */
+		rc = exchange_page_move_mapping(to_page_mapping, from_page_mapping,
+							to_page, from_page, mode, 0, 0);
+
+		if (rc) {
+			if (one_pair->from_page_was_mapped)
+				remove_migration_ptes(from_page, from_page, false);
+			if (one_pair->to_page_was_mapped)
+				remove_migration_ptes(to_page, to_page, false);
+
+			if (one_pair->from_anon_vma)
+				put_anon_vma(one_pair->from_anon_vma);
+			unlock_page(from_page);
+
+			if (one_pair->to_anon_vma)
+				put_anon_vma(one_pair->to_anon_vma);
+			unlock_page(to_page);
+
+			mod_node_page_state(page_pgdat(from_page), NR_ISOLATED_ANON +
+					page_is_file_cache(from_page), -hpage_nr_pages(from_page));
+			putback_lru_page(from_page);
+
+			mod_node_page_state(page_pgdat(to_page), NR_ISOLATED_ANON +
+					page_is_file_cache(to_page), -hpage_nr_pages(to_page));
+			putback_lru_page(to_page);
+
+			one_pair->from_page = NULL;
+			one_pair->to_page = NULL;
+
+			list_move(&one_pair->list, exchange_list_ptr);
+			++nr_failed;
+		}
+	}
+
+	return nr_failed;
+}
+
+static int exchange_page_data_concur(struct list_head *unmapped_list_ptr,
+									enum migrate_mode mode)
+{
+	struct exchange_page_info *one_pair;
+	int num_pages = 0, idx = 0;
+	struct page **src_page_list = NULL, **dst_page_list = NULL;
+	unsigned long size = 0;
+	int rc = -EFAULT;
+
+	if (list_empty(unmapped_list_ptr))
+		return 0;
+
+	/* form page list  */
+	list_for_each_entry(one_pair, unmapped_list_ptr, list) {
+		++num_pages;
+		size += PAGE_SIZE * hpage_nr_pages(one_pair->from_page);
+	}
+
+	src_page_list = kzalloc(sizeof(struct page *)*num_pages, GFP_KERNEL);
+	if (!src_page_list)
+		return -ENOMEM;
+	dst_page_list = kzalloc(sizeof(struct page *)*num_pages, GFP_KERNEL);
+	if (!dst_page_list)
+		return -ENOMEM;
+
+	list_for_each_entry(one_pair, unmapped_list_ptr, list) {
+		src_page_list[idx] = one_pair->from_page;
+		dst_page_list[idx] = one_pair->to_page;
+		++idx;
+	}
+
+	BUG_ON(idx != num_pages);
+
+
+	if (mode & MIGRATE_MT)
+		rc = exchange_page_lists_mthread(dst_page_list, src_page_list,
+				num_pages);
+
+	if (rc) {
+		list_for_each_entry(one_pair, unmapped_list_ptr, list) {
+			if (PageHuge(one_pair->from_page) ||
+				PageTransHuge(one_pair->from_page)) {
+				exchange_huge_page(one_pair->to_page, one_pair->from_page);
+			} else {
+				exchange_highpage(one_pair->to_page, one_pair->from_page);
+			}
+		}
+	}
+
+	kfree(src_page_list);
+	kfree(dst_page_list);
+
+	list_for_each_entry(one_pair, unmapped_list_ptr, list) {
+		exchange_page_flags(one_pair->to_page, one_pair->from_page);
+	}
+
+	return rc;
+}
+
+static int remove_migration_ptes_concur(struct list_head *unmapped_list_ptr)
+{
+	struct exchange_page_info *iterator;
+
+	list_for_each_entry(iterator, unmapped_list_ptr, list) {
+		remove_migration_ptes(iterator->from_page, iterator->to_page, false);
+		remove_migration_ptes(iterator->to_page, iterator->from_page, false);
+
+
+		if (iterator->from_anon_vma)
+			put_anon_vma(iterator->from_anon_vma);
+		unlock_page(iterator->from_page);
+
+
+		if (iterator->to_anon_vma)
+			put_anon_vma(iterator->to_anon_vma);
+		unlock_page(iterator->to_page);
+
+
+		putback_lru_page(iterator->from_page);
+		iterator->from_page = NULL;
+
+		putback_lru_page(iterator->to_page);
+		iterator->to_page = NULL;
+	}
+
+	return 0;
+}
+
+int exchange_pages_concur(struct list_head *exchange_list,
+		enum migrate_mode mode, int reason)
+{
+	struct exchange_page_info *one_pair, *one_pair2;
+	int pass = 0;
+	int retry = 1;
+	int nr_failed = 0;
+	int nr_succeeded = 0;
+	int rc = 0;
+	LIST_HEAD(serialized_list);
+	LIST_HEAD(unmapped_list);
+
+	for(pass = 0; pass < 1 && retry; pass++) {
+		retry = 0;
+
+		/* unmap and get new page for page_mapping(page) == NULL */
+		list_for_each_entry_safe(one_pair, one_pair2, exchange_list, list) {
+			struct page *from_page = one_pair->from_page;
+			struct page *to_page = one_pair->to_page;
+			cond_resched();
+
+			if (page_count(from_page) == 1) {
+				/* page was freed from under us. So we are done  */
+				ClearPageActive(from_page);
+				ClearPageUnevictable(from_page);
+
+				put_page(from_page);
+				dec_node_page_state(from_page, NR_ISOLATED_ANON +
+						page_is_file_cache(from_page));
+
+				if (page_count(to_page) == 1) {
+					ClearPageActive(to_page);
+					ClearPageUnevictable(to_page);
+					put_page(to_page);
+				} else {
+					mod_node_page_state(page_pgdat(to_page), NR_ISOLATED_ANON +
+							page_is_file_cache(to_page), -hpage_nr_pages(to_page));
+					putback_lru_page(to_page);
+				}
+				list_del(&one_pair->list);
+
+				continue;
+			}
+
+			if (page_count(to_page) == 1) {
+				/* page was freed from under us. So we are done  */
+				ClearPageActive(to_page);
+				ClearPageUnevictable(to_page);
+
+				put_page(to_page);
+
+				dec_node_page_state(to_page, NR_ISOLATED_ANON +
+						page_is_file_cache(to_page));
+
+				mod_node_page_state(page_pgdat(from_page), NR_ISOLATED_ANON +
+						page_is_file_cache(from_page), -hpage_nr_pages(from_page));
+				putback_lru_page(from_page);
+
+				list_del(&one_pair->list);
+				continue;
+			}
+		/* We do not exchange huge pages and file-backed pages concurrently */
+			if (PageHuge(one_pair->from_page) || PageHuge(one_pair->to_page)) {
+				rc = -ENODEV;
+			}
+			else if ((page_mapping(one_pair->from_page) != NULL) ||
+					 (page_mapping(one_pair->from_page) != NULL)) {
+				rc = -ENODEV;
+			}
+			else
+				rc = unmap_pair_pages_concur(one_pair, 1, mode);
+
+			switch(rc) {
+			case -ENODEV:
+				list_move(&one_pair->list, &serialized_list);
+				break;
+			case -ENOMEM:
+				goto out;
+			case -EAGAIN:
+				retry++;
+				break;
+			case MIGRATEPAGE_SUCCESS:
+				list_move(&one_pair->list, &unmapped_list);
+				nr_succeeded++;
+				break;
+			default:
+				/*
+				 * Permanent failure (-EBUSY, -ENOSYS, etc.):
+				 * unlike -EAGAIN case, the failed page is
+				 * removed from migration page list and not
+				 * retried in the next outer loop.
+				 */
+				list_move(&one_pair->list, &serialized_list);
+				nr_failed++;
+				break;
+			}
+		}
+
+		/* move page->mapping to new page, only -EAGAIN could happen  */
+		exchange_page_mapping_concur(&unmapped_list, exchange_list, mode);
+
+
+		/* copy pages in unmapped_list */
+		exchange_page_data_concur(&unmapped_list, mode);
+
+
+		/* remove migration pte, if old_page is NULL?, unlock old and new
+		 * pages, put anon_vma, put old and new pages */
+		remove_migration_ptes_concur(&unmapped_list);
+	}
+
+	nr_failed += retry;
+	rc = nr_failed;
+
+	exchange_pages(&serialized_list, mode, reason);
+out:
+	list_splice(&unmapped_list, exchange_list);
+	list_splice(&serialized_list, exchange_list);
+
+	return nr_failed?-EFAULT:0;
+}
diff --git a/mm/exchange_page.c b/mm/exchange_page.c
index 6054697..5dba0a6 100644
--- a/mm/exchange_page.c
+++ b/mm/exchange_page.c
@@ -126,7 +126,6 @@ int exchange_page_lists_mthread(struct page **to, struct page **from, int nr_pag
 	int to_node = page_to_nid(*to);
 	int i;
 	struct copy_page_info *work_items;
-	int nr_pages_per_page = hpage_nr_pages(*from);
 	const struct cpumask *per_node_cpumask = cpumask_of_node(to_node);
 	int cpu_id_list[32] = {0};
 	int cpu;
-- 
2.7.4