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Subject[RFC PATCH 01/31] mm: migrate: Add exchange_pages to exchange two lists of pages.
Date
In stead of using two migrate_pages(), a single exchange_pages() would
be sufficient and without allocating new pages.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
include/linux/ksm.h | 5 +
mm/Makefile | 1 +
mm/exchange.c | 846 ++++++++++++++++++++++++++++++++++++++++++++
mm/internal.h | 6 +
mm/ksm.c | 35 ++
mm/migrate.c | 4 +-
6 files changed, 895 insertions(+), 2 deletions(-)
create mode 100644 mm/exchange.c

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 161e8164abcf..87c5b943a73c 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -53,6 +53,7 @@ struct page *ksm_might_need_to_copy(struct page *page,

void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc);
void ksm_migrate_page(struct page *newpage, struct page *oldpage);
+void ksm_exchange_page(struct page *to_page, struct page *from_page);

#else /* !CONFIG_KSM */

@@ -86,6 +87,10 @@ static inline void rmap_walk_ksm(struct page *page,
static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
{
}
+static inline void ksm_exchange_page(struct page *to_page,
+ struct page *from_page)
+{
+}
#endif /* CONFIG_MMU */
#endif /* !CONFIG_KSM */

diff --git a/mm/Makefile b/mm/Makefile
index d210cc9d6f80..1574ea5743e4 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -43,6 +43,7 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \

obj-y += init-mm.o
obj-y += memblock.o
+obj-y += exchange.o

ifdef CONFIG_MMU
obj-$(CONFIG_ADVISE_SYSCALLS) += madvise.o
diff --git a/mm/exchange.c b/mm/exchange.c
new file mode 100644
index 000000000000..a607348cc6f4
--- /dev/null
+++ b/mm/exchange.c
@@ -0,0 +1,846 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2016 NVIDIA, Zi Yan <ziy@nvidia.com>
+ *
+ * Exchange two in-use pages. Page flags and page->mapping are exchanged
+ * as well. Only anonymous pages are supported.
+ */
+
+#include <linux/syscalls.h>
+#include <linux/migrate.h>
+#include <linux/security.h>
+#include <linux/cpuset.h>
+#include <linux/hugetlb.h>
+#include <linux/mm_inline.h>
+#include <linux/page_idle.h>
+#include <linux/page-flags.h>
+#include <linux/ksm.h>
+#include <linux/memcontrol.h>
+#include <linux/balloon_compaction.h>
+#include <linux/buffer_head.h>
+#include <linux/fs.h> /* buffer_migrate_page */
+#include <linux/backing-dev.h>
+
+
+#include "internal.h"
+
+struct exchange_page_info {
+ struct page *from_page;
+ struct page *to_page;
+
+ struct anon_vma *from_anon_vma;
+ struct anon_vma *to_anon_vma;
+
+ struct list_head list;
+};
+
+struct page_flags {
+ unsigned int page_error :1;
+ unsigned int page_referenced:1;
+ unsigned int page_uptodate:1;
+ unsigned int page_active:1;
+ unsigned int page_unevictable:1;
+ unsigned int page_checked:1;
+ unsigned int page_mappedtodisk:1;
+ unsigned int page_dirty:1;
+ unsigned int page_is_young:1;
+ unsigned int page_is_idle:1;
+ unsigned int page_swapcache:1;
+ unsigned int page_writeback:1;
+ unsigned int page_private:1;
+ unsigned int __pad:3;
+};
+
+
+static void exchange_page(char *to, char *from)
+{
+ u64 tmp;
+ int i;
+
+ for (i = 0; i < PAGE_SIZE; i += sizeof(tmp)) {
+ tmp = *((u64 *)(from + i));
+ *((u64 *)(from + i)) = *((u64 *)(to + i));
+ *((u64 *)(to + i)) = tmp;
+ }
+}
+
+static inline void exchange_highpage(struct page *to, struct page *from)
+{
+ char *vfrom, *vto;
+
+ vfrom = kmap_atomic(from);
+ vto = kmap_atomic(to);
+ exchange_page(vto, vfrom);
+ kunmap_atomic(vto);
+ kunmap_atomic(vfrom);
+}
+
+static void __exchange_gigantic_page(struct page *dst, struct page *src,
+ int nr_pages)
+{
+ int i;
+ struct page *dst_base = dst;
+ struct page *src_base = src;
+
+ for (i = 0; i < nr_pages; ) {
+ cond_resched();
+ exchange_highpage(dst, src);
+
+ i++;
+ dst = mem_map_next(dst, dst_base, i);
+ src = mem_map_next(src, src_base, i);
+ }
+}
+
+static void exchange_huge_page(struct page *dst, struct page *src)
+{
+ int i;
+ int nr_pages;
+
+ if (PageHuge(src)) {
+ /* hugetlbfs page */
+ struct hstate *h = page_hstate(src);
+
+ nr_pages = pages_per_huge_page(h);
+
+ if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
+ __exchange_gigantic_page(dst, src, nr_pages);
+ return;
+ }
+ } else {
+ /* thp page */
+ VM_BUG_ON(!PageTransHuge(src));
+ nr_pages = hpage_nr_pages(src);
+ }
+
+ for (i = 0; i < nr_pages; i++) {
+ cond_resched();
+ exchange_highpage(dst + i, src + i);
+ }
+}
+
+/*
+ * Copy the page to its new location without polluting cache
+ */
+static void exchange_page_flags(struct page *to_page, struct page *from_page)
+{
+ int from_cpupid, to_cpupid;
+ struct page_flags from_page_flags, to_page_flags;
+ struct mem_cgroup *to_memcg = page_memcg(to_page),
+ *from_memcg = page_memcg(from_page);
+
+ from_cpupid = page_cpupid_xchg_last(from_page, -1);
+
+ from_page_flags.page_error = TestClearPageError(from_page);
+ from_page_flags.page_referenced = TestClearPageReferenced(from_page);
+ from_page_flags.page_uptodate = PageUptodate(from_page);
+ ClearPageUptodate(from_page);
+ from_page_flags.page_active = TestClearPageActive(from_page);
+ from_page_flags.page_unevictable = TestClearPageUnevictable(from_page);
+ from_page_flags.page_checked = PageChecked(from_page);
+ ClearPageChecked(from_page);
+ from_page_flags.page_mappedtodisk = PageMappedToDisk(from_page);
+ ClearPageMappedToDisk(from_page);
+ from_page_flags.page_dirty = PageDirty(from_page);
+ ClearPageDirty(from_page);
+ from_page_flags.page_is_young = test_and_clear_page_young(from_page);
+ from_page_flags.page_is_idle = page_is_idle(from_page);
+ clear_page_idle(from_page);
+ from_page_flags.page_swapcache = PageSwapCache(from_page);
+ from_page_flags.page_writeback = test_clear_page_writeback(from_page);
+
+
+ to_cpupid = page_cpupid_xchg_last(to_page, -1);
+
+ to_page_flags.page_error = TestClearPageError(to_page);
+ to_page_flags.page_referenced = TestClearPageReferenced(to_page);
+ to_page_flags.page_uptodate = PageUptodate(to_page);
+ ClearPageUptodate(to_page);
+ to_page_flags.page_active = TestClearPageActive(to_page);
+ to_page_flags.page_unevictable = TestClearPageUnevictable(to_page);
+ to_page_flags.page_checked = PageChecked(to_page);
+ ClearPageChecked(to_page);
+ to_page_flags.page_mappedtodisk = PageMappedToDisk(to_page);
+ ClearPageMappedToDisk(to_page);
+ to_page_flags.page_dirty = PageDirty(to_page);
+ ClearPageDirty(to_page);
+ to_page_flags.page_is_young = test_and_clear_page_young(to_page);
+ to_page_flags.page_is_idle = page_is_idle(to_page);
+ clear_page_idle(to_page);
+ to_page_flags.page_swapcache = PageSwapCache(to_page);
+ to_page_flags.page_writeback = test_clear_page_writeback(to_page);
+
+ /* set to_page */
+ if (from_page_flags.page_error)
+ SetPageError(to_page);
+ if (from_page_flags.page_referenced)
+ SetPageReferenced(to_page);
+ if (from_page_flags.page_uptodate)
+ SetPageUptodate(to_page);
+ if (from_page_flags.page_active) {
+ VM_BUG_ON_PAGE(from_page_flags.page_unevictable, from_page);
+ SetPageActive(to_page);
+ } else if (from_page_flags.page_unevictable)
+ SetPageUnevictable(to_page);
+ if (from_page_flags.page_checked)
+ SetPageChecked(to_page);
+ if (from_page_flags.page_mappedtodisk)
+ SetPageMappedToDisk(to_page);
+
+ /* Move dirty on pages not done by migrate_page_move_mapping() */
+ if (from_page_flags.page_dirty)
+ SetPageDirty(to_page);
+
+ if (from_page_flags.page_is_young)
+ set_page_young(to_page);
+ if (from_page_flags.page_is_idle)
+ set_page_idle(to_page);
+
+ /* set from_page */
+ if (to_page_flags.page_error)
+ SetPageError(from_page);
+ if (to_page_flags.page_referenced)
+ SetPageReferenced(from_page);
+ if (to_page_flags.page_uptodate)
+ SetPageUptodate(from_page);
+ if (to_page_flags.page_active) {
+ VM_BUG_ON_PAGE(to_page_flags.page_unevictable, from_page);
+ SetPageActive(from_page);
+ } else if (to_page_flags.page_unevictable)
+ SetPageUnevictable(from_page);
+ if (to_page_flags.page_checked)
+ SetPageChecked(from_page);
+ if (to_page_flags.page_mappedtodisk)
+ SetPageMappedToDisk(from_page);
+
+ /* Move dirty on pages not done by migrate_page_move_mapping() */
+ if (to_page_flags.page_dirty)
+ SetPageDirty(from_page);
+
+ if (to_page_flags.page_is_young)
+ set_page_young(from_page);
+ if (to_page_flags.page_is_idle)
+ set_page_idle(from_page);
+
+ /*
+ * Copy NUMA information to the new page, to prevent over-eager
+ * future migrations of this same page.
+ */
+ page_cpupid_xchg_last(to_page, from_cpupid);
+ page_cpupid_xchg_last(from_page, to_cpupid);
+
+ ksm_exchange_page(to_page, from_page);
+ /*
+ * Please do not reorder this without considering how mm/ksm.c's
+ * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
+ */
+ ClearPageSwapCache(to_page);
+ ClearPageSwapCache(from_page);
+ if (from_page_flags.page_swapcache)
+ SetPageSwapCache(to_page);
+ if (to_page_flags.page_swapcache)
+ SetPageSwapCache(from_page);
+
+
+#ifdef CONFIG_PAGE_OWNER
+ /* exchange page owner */
+ BUILD_BUG();
+#endif
+ /* exchange mem cgroup */
+ to_page->mem_cgroup = from_memcg;
+ from_page->mem_cgroup = to_memcg;
+
+}
+
+/*
+ * Replace the page in the mapping.
+ *
+ * The number of remaining references must be:
+ * 1 for anonymous pages without a mapping
+ * 2 for pages with a mapping
+ * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
+ */
+
+static int exchange_page_move_mapping(struct address_space *to_mapping,
+ struct address_space *from_mapping,
+ struct page *to_page, struct page *from_page,
+ struct buffer_head *to_head,
+ struct buffer_head *from_head,
+ enum migrate_mode mode,
+ int to_extra_count, int from_extra_count)
+{
+ int to_expected_count = 1 + to_extra_count,
+ from_expected_count = 1 + from_extra_count;
+ unsigned long from_page_index = from_page->index;
+ unsigned long to_page_index = to_page->index;
+ int to_swapbacked = PageSwapBacked(to_page),
+ from_swapbacked = PageSwapBacked(from_page);
+ struct address_space *to_mapping_value = to_page->mapping;
+ struct address_space *from_mapping_value = from_page->mapping;
+
+ VM_BUG_ON_PAGE(to_mapping != page_mapping(to_page), to_page);
+ VM_BUG_ON_PAGE(from_mapping != page_mapping(from_page), from_page);
+
+ if (!to_mapping) {
+ /* Anonymous page without mapping */
+ if (page_count(to_page) != to_expected_count)
+ return -EAGAIN;
+ }
+
+ if (!from_mapping) {
+ /* Anonymous page without mapping */
+ if (page_count(from_page) != from_expected_count)
+ return -EAGAIN;
+ }
+
+ /* both are anonymous pages */
+ if (!from_mapping && !to_mapping) {
+ /* from_page */
+ from_page->index = to_page_index;
+ from_page->mapping = to_mapping_value;
+
+ ClearPageSwapBacked(from_page);
+ if (to_swapbacked)
+ SetPageSwapBacked(from_page);
+
+
+ /* to_page */
+ to_page->index = from_page_index;
+ to_page->mapping = from_mapping_value;
+
+ ClearPageSwapBacked(to_page);
+ if (from_swapbacked)
+ SetPageSwapBacked(to_page);
+ } else if (!from_mapping && to_mapping) {
+ /* from is anonymous, to is file-backed */
+ struct zone *from_zone, *to_zone;
+ void **to_pslot;
+ int dirty;
+
+ from_zone = page_zone(from_page);
+ to_zone = page_zone(to_page);
+
+ xa_lock_irq(&to_mapping->i_pages);
+
+ to_pslot = radix_tree_lookup_slot(&to_mapping->i_pages,
+ page_index(to_page));
+
+ to_expected_count += 1 + page_has_private(to_page);
+ if (page_count(to_page) != to_expected_count ||
+ radix_tree_deref_slot_protected(to_pslot,
+ &to_mapping->i_pages.xa_lock) != to_page) {
+ xa_unlock_irq(&to_mapping->i_pages);
+ return -EAGAIN;
+ }
+
+ if (!page_ref_freeze(to_page, to_expected_count)) {
+ xa_unlock_irq(&to_mapping->i_pages);
+ pr_debug("cannot freeze page count\n");
+ return -EAGAIN;
+ }
+
+ if (mode == MIGRATE_ASYNC && to_head &&
+ !buffer_migrate_lock_buffers(to_head, mode)) {
+ page_ref_unfreeze(to_page, to_expected_count);
+ xa_unlock_irq(&to_mapping->i_pages);
+
+ pr_debug("cannot lock buffer head\n");
+ return -EAGAIN;
+ }
+
+ if (!page_ref_freeze(from_page, from_expected_count)) {
+ page_ref_unfreeze(to_page, to_expected_count);
+ xa_unlock_irq(&to_mapping->i_pages);
+
+ return -EAGAIN;
+ }
+ /*
+ * Now we know that no one else is looking at the page:
+ * no turning back from here.
+ */
+ ClearPageSwapBacked(from_page);
+ ClearPageSwapBacked(to_page);
+
+ /* from_page */
+ from_page->index = to_page_index;
+ from_page->mapping = to_mapping_value;
+ /* to_page */
+ to_page->index = from_page_index;
+ to_page->mapping = from_mapping_value;
+
+ if (to_swapbacked)
+ __SetPageSwapBacked(from_page);
+ else
+ VM_BUG_ON_PAGE(PageSwapCache(to_page), to_page);
+
+ if (from_swapbacked)
+ __SetPageSwapBacked(to_page);
+ else
+ VM_BUG_ON_PAGE(PageSwapCache(from_page), from_page);
+
+ dirty = PageDirty(to_page);
+
+ radix_tree_replace_slot(&to_mapping->i_pages,
+ to_pslot, from_page);
+
+ /* move cache reference */
+ page_ref_unfreeze(to_page, to_expected_count - 1);
+ page_ref_unfreeze(from_page, from_expected_count + 1);
+
+ xa_unlock(&to_mapping->i_pages);
+
+ /*
+ * If moved to a different zone then also account
+ * the page for that zone. Other VM counters will be
+ * taken care of when we establish references to the
+ * new page and drop references to the old page.
+ *
+ * Note that anonymous pages are accounted for
+ * via NR_FILE_PAGES and NR_ANON_MAPPED if they
+ * are mapped to swap space.
+ */
+ if (to_zone != from_zone) {
+ __dec_node_state(to_zone->zone_pgdat, NR_FILE_PAGES);
+ __inc_node_state(from_zone->zone_pgdat, NR_FILE_PAGES);
+ if (PageSwapBacked(to_page) && !PageSwapCache(to_page)) {
+ __dec_node_state(to_zone->zone_pgdat, NR_SHMEM);
+ __inc_node_state(from_zone->zone_pgdat, NR_SHMEM);
+ }
+ if (dirty && mapping_cap_account_dirty(to_mapping)) {
+ __dec_node_state(to_zone->zone_pgdat, NR_FILE_DIRTY);
+ __dec_zone_state(to_zone, NR_ZONE_WRITE_PENDING);
+ __inc_node_state(from_zone->zone_pgdat, NR_FILE_DIRTY);
+ __inc_zone_state(from_zone, NR_ZONE_WRITE_PENDING);
+ }
+ }
+ local_irq_enable();
+
+ } else {
+ /* from is file-backed to is anonymous: fold this to the case above */
+ /* both are file-backed */
+ VM_BUG_ON(1);
+ }
+
+ return MIGRATEPAGE_SUCCESS;
+}
+
+static int exchange_from_to_pages(struct page *to_page, struct page *from_page,
+ enum migrate_mode mode)
+{
+ int rc = -EBUSY;
+ struct address_space *to_page_mapping, *from_page_mapping;
+ struct buffer_head *to_head = NULL, *to_bh = NULL;
+
+ 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);
+
+ /* from_page has to be anonymous page */
+ VM_BUG_ON(from_page_mapping);
+ VM_BUG_ON(PageWriteback(from_page));
+ /* writeback has to finish */
+ BUG_ON(PageWriteback(to_page));
+
+
+ /* to_page is anonymous */
+ if (!to_page_mapping) {
+exchange_mappings:
+ /* actual page mapping exchange */
+ rc = exchange_page_move_mapping(to_page_mapping, from_page_mapping,
+ to_page, from_page, NULL, NULL, mode, 0, 0);
+ } else {
+ if (to_page_mapping->a_ops->migratepage == buffer_migrate_page) {
+
+ if (!page_has_buffers(to_page))
+ goto exchange_mappings;
+
+ to_head = page_buffers(to_page);
+
+ rc = exchange_page_move_mapping(to_page_mapping,
+ from_page_mapping, to_page, from_page,
+ to_head, NULL, mode, 0, 0);
+
+ if (rc != MIGRATEPAGE_SUCCESS)
+ return rc;
+
+ /*
+ * In the async case, migrate_page_move_mapping locked the buffers
+ * with an IRQ-safe spinlock held. In the sync case, the buffers
+ * need to be locked now
+ */
+ if (mode != MIGRATE_ASYNC)
+ VM_BUG_ON(!buffer_migrate_lock_buffers(to_head, mode));
+
+ ClearPagePrivate(to_page);
+ set_page_private(from_page, page_private(to_page));
+ set_page_private(to_page, 0);
+ /* transfer private page count */
+ put_page(to_page);
+ get_page(from_page);
+
+ to_bh = to_head;
+ do {
+ set_bh_page(to_bh, from_page, bh_offset(to_bh));
+ to_bh = to_bh->b_this_page;
+
+ } while (to_bh != to_head);
+
+ SetPagePrivate(from_page);
+
+ to_bh = to_head;
+ } else if (!to_page_mapping->a_ops->migratepage) {
+ /* fallback_migrate_page */
+ if (PageDirty(to_page)) {
+ if (mode != MIGRATE_SYNC)
+ return -EBUSY;
+ return writeout(to_page_mapping, to_page);
+ }
+ if (page_has_private(to_page) &&
+ !try_to_release_page(to_page, GFP_KERNEL))
+ return -EAGAIN;
+
+ goto exchange_mappings;
+ }
+ }
+ /* actual page data exchange */
+ if (rc != MIGRATEPAGE_SUCCESS)
+ return rc;
+
+
+ if (PageHuge(from_page) || PageTransHuge(from_page))
+ exchange_huge_page(to_page, from_page);
+ else
+ exchange_highpage(to_page, from_page);
+ rc = 0;
+
+ /*
+ * 1. buffer_migrate_page:
+ * private flag should be transferred from to_page to from_page
+ *
+ * 2. anon<->anon, fallback_migrate_page:
+ * both have none private flags or to_page's is cleared.
+ */
+ VM_BUG_ON(!((page_has_private(from_page) && !page_has_private(to_page)) ||
+ (!page_has_private(from_page) && !page_has_private(to_page))));
+
+ exchange_page_flags(to_page, from_page);
+
+ if (to_bh) {
+ VM_BUG_ON(to_bh != to_head);
+ do {
+ unlock_buffer(to_bh);
+ put_bh(to_bh);
+ to_bh = to_bh->b_this_page;
+
+ } while (to_bh != to_head);
+ }
+
+ return rc;
+}
+
+static int unmap_and_exchange(struct page *from_page,
+ struct page *to_page, enum migrate_mode mode)
+{
+ int rc = -EAGAIN;
+ struct anon_vma *from_anon_vma = NULL;
+ struct anon_vma *to_anon_vma = NULL;
+ int from_page_was_mapped = 0;
+ int to_page_was_mapped = 0;
+ int from_page_count = 0, to_page_count = 0;
+ int from_map_count = 0, to_map_count = 0;
+ unsigned long from_flags, to_flags;
+ pgoff_t from_index, to_index;
+ struct address_space *from_mapping, *to_mapping;
+
+ if (!trylock_page(from_page)) {
+ if (mode == MIGRATE_ASYNC)
+ goto out;
+ lock_page(from_page);
+ }
+
+ if (!trylock_page(to_page)) {
+ if (mode == MIGRATE_ASYNC)
+ goto out_unlock;
+ lock_page(to_page);
+ }
+
+ /* from_page is supposed to be an anonymous page */
+ VM_BUG_ON_PAGE(PageWriteback(from_page), from_page);
+
+ if (PageWriteback(to_page)) {
+ /*
+ * Only in the case of a full synchronous migration is it
+ * necessary to wait for PageWriteback. In the async case,
+ * the retry loop is too short and in the sync-light case,
+ * the overhead of stalling is too much
+ */
+ if (mode != MIGRATE_SYNC) {
+ rc = -EBUSY;
+ goto out_unlock_both;
+ }
+ wait_on_page_writeback(to_page);
+ }
+
+ if (PageAnon(from_page) && !PageKsm(from_page))
+ from_anon_vma = page_get_anon_vma(from_page);
+
+ if (PageAnon(to_page) && !PageKsm(to_page))
+ to_anon_vma = page_get_anon_vma(to_page);
+
+ from_page_count = page_count(from_page);
+ from_map_count = page_mapcount(from_page);
+ to_page_count = page_count(to_page);
+ to_map_count = page_mapcount(to_page);
+ from_flags = from_page->flags;
+ to_flags = to_page->flags;
+ from_mapping = from_page->mapping;
+ to_mapping = to_page->mapping;
+ from_index = from_page->index;
+ to_index = to_page->index;
+
+ /*
+ * 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) &&
+ !from_anon_vma, from_page);
+ try_to_unmap(from_page,
+ TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ 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_remove_from_migration_pte;
+ }
+ } else if (page_mapped(to_page)) {
+ /* Establish migration ptes */
+ VM_BUG_ON_PAGE(PageAnon(to_page) && !PageKsm(to_page) &&
+ !to_anon_vma, to_page);
+ try_to_unmap(to_page,
+ TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
+ to_page_was_mapped = 1;
+ }
+
+ if (!page_mapped(from_page) && !page_mapped(to_page))
+ rc = exchange_from_to_pages(to_page, from_page, mode);
+
+
+ if (to_page_was_mapped) {
+ /* swap back to_page->index to be compatible with
+ * remove_migration_ptes(), which assumes both from_page and to_page
+ * below have the same index.
+ */
+ if (rc == MIGRATEPAGE_SUCCESS)
+ swap(to_page->index, to_index);
+
+ remove_migration_ptes(to_page,
+ rc == MIGRATEPAGE_SUCCESS ? from_page : to_page, false);
+
+ if (rc == MIGRATEPAGE_SUCCESS)
+ swap(to_page->index, to_index);
+ }
+
+out_unlock_both_remove_from_migration_pte:
+ if (from_page_was_mapped) {
+ /* swap back from_page->index to be compatible with
+ * remove_migration_ptes(), which assumes both from_page and to_page
+ * below have the same index.
+ */
+ if (rc == MIGRATEPAGE_SUCCESS)
+ swap(from_page->index, from_index);
+
+ remove_migration_ptes(from_page,
+ rc == MIGRATEPAGE_SUCCESS ? to_page : from_page, false);
+
+ if (rc == MIGRATEPAGE_SUCCESS)
+ swap(from_page->index, from_index);
+ }
+
+out_unlock_both:
+ if (to_anon_vma)
+ put_anon_vma(to_anon_vma);
+ unlock_page(to_page);
+out_unlock:
+ /* Drop an anon_vma reference if we took one */
+ if (from_anon_vma)
+ put_anon_vma(from_anon_vma);
+ unlock_page(from_page);
+out:
+ return rc;
+}
+
+/*
+ * Exchange pages in the exchange_list
+ *
+ * Caller should release the exchange_list resource.
+ *
+ */
+static int exchange_pages(struct list_head *exchange_list,
+ enum migrate_mode mode,
+ int reason)
+{
+ struct exchange_page_info *one_pair, *one_pair2;
+ int failed = 0;
+
+ 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;
+ int rc;
+ int retry = 0;
+
+again:
+ if (page_count(from_page) == 1) {
+ /* page was freed from under us. So we are done */
+ ClearPageActive(from_page);
+ ClearPageUnevictable(from_page);
+
+ mod_node_page_state(page_pgdat(from_page), NR_ISOLATED_ANON +
+ page_is_file_cache(from_page),
+ -hpage_nr_pages(from_page));
+ put_page(from_page);
+
+ if (page_count(to_page) == 1) {
+ ClearPageActive(to_page);
+ ClearPageUnevictable(to_page);
+ put_page(to_page);
+ mod_node_page_state(page_pgdat(to_page), NR_ISOLATED_ANON +
+ page_is_file_cache(to_page),
+ -hpage_nr_pages(to_page));
+ } else
+ goto putback_to_page;
+
+ continue;
+ }
+
+ if (page_count(to_page) == 1) {
+ /* page was freed from under us. So we are done */
+ ClearPageActive(to_page);
+ ClearPageUnevictable(to_page);
+
+ mod_node_page_state(page_pgdat(to_page), NR_ISOLATED_ANON +
+ page_is_file_cache(to_page),
+ -hpage_nr_pages(to_page));
+ put_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);
+ continue;
+ }
+
+ /* TODO: compound page not supported */
+ /* to_page can be file-backed page */
+ if (PageCompound(from_page) ||
+ page_mapping(from_page)
+ ) {
+ ++failed;
+ goto putback;
+ }
+
+ rc = unmap_and_exchange(from_page, to_page, mode);
+
+ if (rc == -EAGAIN && retry < 3) {
+ ++retry;
+ goto again;
+ }
+
+ if (rc != MIGRATEPAGE_SUCCESS)
+ ++failed;
+
+putback:
+ 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);
+putback_to_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);
+ }
+ return failed;
+}
+
+int exchange_two_pages(struct page *page1, struct page *page2)
+{
+ struct exchange_page_info page_info;
+ LIST_HEAD(exchange_list);
+ int err = -EFAULT;
+ int pagevec_flushed = 0;
+
+ VM_BUG_ON_PAGE(PageTail(page1), page1);
+ VM_BUG_ON_PAGE(PageTail(page2), page2);
+
+ if (!(PageLRU(page1) && PageLRU(page2)))
+ return -EBUSY;
+
+retry_isolate1:
+ if (!get_page_unless_zero(page1))
+ return -EBUSY;
+ err = isolate_lru_page(page1);
+ put_page(page1);
+ if (err) {
+ if (!pagevec_flushed) {
+ migrate_prep();
+ pagevec_flushed = 1;
+ goto retry_isolate1;
+ }
+ return err;
+ }
+ mod_node_page_state(page_pgdat(page1),
+ NR_ISOLATED_ANON + page_is_file_cache(page1),
+ hpage_nr_pages(page1));
+
+retry_isolate2:
+ if (!get_page_unless_zero(page2)) {
+ putback_lru_page(page1);
+ return -EBUSY;
+ }
+ err = isolate_lru_page(page2);
+ put_page(page2);
+ if (err) {
+ if (!pagevec_flushed) {
+ migrate_prep();
+ pagevec_flushed = 1;
+ goto retry_isolate2;
+ }
+ return err;
+ }
+ mod_node_page_state(page_pgdat(page2),
+ NR_ISOLATED_ANON + page_is_file_cache(page2),
+ hpage_nr_pages(page2));
+
+ page_info.from_page = page1;
+ page_info.to_page = page2;
+ INIT_LIST_HEAD(&page_info.list);
+ list_add(&page_info.list, &exchange_list);
+
+
+ return exchange_pages(&exchange_list, MIGRATE_SYNC, 0);
+
+}
diff --git a/mm/internal.h b/mm/internal.h
index f4a7bb02decf..77e205c423ce 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -543,4 +543,10 @@ static inline bool is_migrate_highatomic_page(struct page *page)

void setup_zone_pageset(struct zone *zone);
extern struct page *alloc_new_node_page(struct page *page, unsigned long node);
+
+bool buffer_migrate_lock_buffers(struct buffer_head *head,
+ enum migrate_mode mode);
+int writeout(struct address_space *mapping, struct page *page);
+extern int exchange_two_pages(struct page *page1, struct page *page2);
+
#endif /* __MM_INTERNAL_H */
diff --git a/mm/ksm.c b/mm/ksm.c
index 6c48ad13b4c9..dc1ec06b71a0 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2665,6 +2665,41 @@ void ksm_migrate_page(struct page *newpage, struct page *oldpage)
set_page_stable_node(oldpage, NULL);
}
}
+
+void ksm_exchange_page(struct page *to_page, struct page *from_page)
+{
+ struct stable_node *to_stable_node, *from_stable_node;
+
+ VM_BUG_ON_PAGE(!PageLocked(to_page), to_page);
+ VM_BUG_ON_PAGE(!PageLocked(from_page), from_page);
+
+ to_stable_node = page_stable_node(to_page);
+ from_stable_node = page_stable_node(from_page);
+ if (to_stable_node) {
+ VM_BUG_ON_PAGE(to_stable_node->kpfn != page_to_pfn(from_page),
+ from_page);
+ to_stable_node->kpfn = page_to_pfn(to_page);
+ /*
+ * newpage->mapping was set in advance; now we need smp_wmb()
+ * to make sure that the new stable_node->kpfn is visible
+ * to get_ksm_page() before it can see that oldpage->mapping
+ * has gone stale (or that PageSwapCache has been cleared).
+ */
+ smp_wmb();
+ }
+ if (from_stable_node) {
+ VM_BUG_ON_PAGE(from_stable_node->kpfn != page_to_pfn(to_page),
+ to_page);
+ from_stable_node->kpfn = page_to_pfn(from_page);
+ /*
+ * newpage->mapping was set in advance; now we need smp_wmb()
+ * to make sure that the new stable_node->kpfn is visible
+ * to get_ksm_page() before it can see that oldpage->mapping
+ * has gone stale (or that PageSwapCache has been cleared).
+ */
+ smp_wmb();
+ }
+}
#endif /* CONFIG_MIGRATION */

#ifdef CONFIG_MEMORY_HOTREMOVE
diff --git a/mm/migrate.c b/mm/migrate.c
index d4fd680be3b0..b8c79aa62134 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -701,7 +701,7 @@ EXPORT_SYMBOL(migrate_page);

#ifdef CONFIG_BLOCK
/* Returns true if all buffers are successfully locked */
-static bool buffer_migrate_lock_buffers(struct buffer_head *head,
+bool buffer_migrate_lock_buffers(struct buffer_head *head,
enum migrate_mode mode)
{
struct buffer_head *bh = head;
@@ -849,7 +849,7 @@ int buffer_migrate_page_norefs(struct address_space *mapping,
/*
* Writeback a page to clean the dirty state
*/
-static int writeout(struct address_space *mapping, struct page *page)
+int writeout(struct address_space *mapping, struct page *page)
{
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
--
2.20.1
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