mm: migrate: support non-lru movable page migration

We have allowed migration for only LRU pages until now and it was enough
to make high-order pages.  But recently, embedded system(e.g., webOS,
android) uses lots of non-movable pages(e.g., zram, GPU memory) so we
have seen several reports about troubles of small high-order allocation.
For fixing the problem, there were several efforts (e,g,.  enhance
compaction algorithm, SLUB fallback to 0-order page, reserved memory,
vmalloc and so on) but if there are lots of non-movable pages in system,
their solutions are void in the long run.

So, this patch is to support facility to change non-movable pages with
movable.  For the feature, this patch introduces functions related to
migration to address_space_operations as well as some page flags.

If a driver want to make own pages movable, it should define three
functions which are function pointers of struct
address_space_operations.

1. bool (*isolate_page) (struct page *page, isolate_mode_t mode);

What VM expects on isolate_page function of driver is to return *true*
if driver isolates page successfully.  On returing true, VM marks the
page as PG_isolated so concurrent isolation in several CPUs skip the
page for isolation.  If a driver cannot isolate the page, it should
return *false*.

Once page is successfully isolated, VM uses page.lru fields so driver
shouldn't expect to preserve values in that fields.

2. int (*migratepage) (struct address_space *mapping,
		struct page *newpage, struct page *oldpage, enum migrate_mode);

After isolation, VM calls migratepage of driver with isolated page.  The
function of migratepage is to move content of the old page to new page
and set up fields of struct page newpage.  Keep in mind that you should
indicate to the VM the oldpage is no longer movable via
__ClearPageMovable() under page_lock if you migrated the oldpage
successfully and returns 0.  If driver cannot migrate the page at the
moment, driver can return -EAGAIN.  On -EAGAIN, VM will retry page
migration in a short time because VM interprets -EAGAIN as "temporal
migration failure".  On returning any error except -EAGAIN, VM will give
up the page migration without retrying in this time.

Driver shouldn't touch page.lru field VM using in the functions.

3. void (*putback_page)(struct page *);

If migration fails on isolated page, VM should return the isolated page
to the driver so VM calls driver's putback_page with migration failed
page.  In this function, driver should put the isolated page back to the
own data structure.

4. non-lru movable page flags

There are two page flags for supporting non-lru movable page.

* PG_movable

Driver should use the below function to make page movable under
page_lock.

	void __SetPageMovable(struct page *page, struct address_space *mapping)

It needs argument of address_space for registering migration family
functions which will be called by VM.  Exactly speaking, PG_movable is
not a real flag of struct page.  Rather than, VM reuses page->mapping's
lower bits to represent it.

	#define PAGE_MAPPING_MOVABLE 0x2
	page->mapping = page->mapping | PAGE_MAPPING_MOVABLE;

so driver shouldn't access page->mapping directly.  Instead, driver
should use page_mapping which mask off the low two bits of page->mapping
so it can get right struct address_space.

For testing of non-lru movable page, VM supports __PageMovable function.
However, it doesn't guarantee to identify non-lru movable page because
page->mapping field is unified with other variables in struct page.  As
well, if driver releases the page after isolation by VM, page->mapping
doesn't have stable value although it has PAGE_MAPPING_MOVABLE (Look at
__ClearPageMovable).  But __PageMovable is cheap to catch whether page
is LRU or non-lru movable once the page has been isolated.  Because LRU
pages never can have PAGE_MAPPING_MOVABLE in page->mapping.  It is also
good for just peeking to test non-lru movable pages before more
expensive checking with lock_page in pfn scanning to select victim.

For guaranteeing non-lru movable page, VM provides PageMovable function.
Unlike __PageMovable, PageMovable functions validates page->mapping and
mapping->a_ops->isolate_page under lock_page.  The lock_page prevents
sudden destroying of page->mapping.

Driver using __SetPageMovable should clear the flag via
__ClearMovablePage under page_lock before the releasing the page.

* PG_isolated

To prevent concurrent isolation among several CPUs, VM marks isolated
page as PG_isolated under lock_page.  So if a CPU encounters PG_isolated
non-lru movable page, it can skip it.  Driver doesn't need to manipulate
the flag because VM will set/clear it automatically.  Keep in mind that
if driver sees PG_isolated page, it means the page have been isolated by
VM so it shouldn't touch page.lru field.  PG_isolated is alias with
PG_reclaim flag so driver shouldn't use the flag for own purpose.

[opensource.ganesh@gmail.com: mm/compaction: remove local variable is_lru]
  Link: http://lkml.kernel.org/r/20160618014841.GA7422@leo-test
Link: http://lkml.kernel.org/r/1464736881-24886-3-git-send-email-minchan@kernel.org
Signed-off-by: Gioh Kim <gi-oh.kim@profitbricks.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: John Einar Reitan <john.reitan@foss.arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 174 insertions, 18 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index c74412b381ff..8119fdc563f8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -31,6 +31,7 @@
 #include <linux/vmalloc.h>
 #include <linux/security.h>
 #include <linux/backing-dev.h>
+#include <linux/compaction.h>
 #include <linux/syscalls.h>
 #include <linux/hugetlb.h>
 #include <linux/hugetlb_cgroup.h>
@@ -73,6 +74,81 @@ int migrate_prep_local(void)
         return 0;
 }
 
+bool isolate_movable_page(struct page *page, isolate_mode_t mode)
+{
+        struct address_space *mapping;
+
+        /*
+         * Avoid burning cycles with pages that are yet under __free_pages(),
+         * or just got freed under us.
+         *
+         * In case we 'win' a race for a movable page being freed under us and
+         * raise its refcount preventing __free_pages() from doing its job
+         * the put_page() at the end of this block will take care of
+         * release this page, thus avoiding a nasty leakage.
+         */
+        if (unlikely(!get_page_unless_zero(page)))
+                goto out;
+
+        /*
+         * Check PageMovable before holding a PG_lock because page's owner
+         * assumes anybody doesn't touch PG_lock of newly allocated page
+         * so unconditionally grapping the lock ruins page's owner side.
+         */
+        if (unlikely(!__PageMovable(page)))
+                goto out_putpage;
+        /*
+         * As movable pages are not isolated from LRU lists, concurrent
+         * compaction threads can race against page migration functions
+         * as well as race against the releasing a page.
+         *
+         * In order to avoid having an already isolated movable page
+         * being (wrongly) re-isolated while it is under migration,
+         * or to avoid attempting to isolate pages being released,
+         * lets be sure we have the page lock
+         * before proceeding with the movable page isolation steps.
+         */
+        if (unlikely(!trylock_page(page)))
+                goto out_putpage;
+
+        if (!PageMovable(page) || PageIsolated(page))
+                goto out_no_isolated;
+
+        mapping = page_mapping(page);
+        VM_BUG_ON_PAGE(!mapping, page);
+
+        if (!mapping->a_ops->isolate_page(page, mode))
+                goto out_no_isolated;
+
+        /* Driver shouldn't use PG_isolated bit of page->flags */
+        WARN_ON_ONCE(PageIsolated(page));
+        __SetPageIsolated(page);
+        unlock_page(page);
+
+        return true;
+
+out_no_isolated:
+        unlock_page(page);
+out_putpage:
+        put_page(page);
+out:
+        return false;
+}
+
+/* It should be called on page which is PG_movable */
+void putback_movable_page(struct page *page)
+{
+        struct address_space *mapping;
+
+        VM_BUG_ON_PAGE(!PageLocked(page), page);
+        VM_BUG_ON_PAGE(!PageMovable(page), page);
+        VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+        mapping = page_mapping(page);
+        mapping->a_ops->putback_page(page);
+        __ClearPageIsolated(page);
+}
+
 /*
  * Put previously isolated pages back onto the appropriate lists
  * from where they were once taken off for compaction/migration.
@@ -94,10 +170,25 @@ void putback_movable_pages(struct list_head *l)
                 list_del(&page->lru);
                 dec_zone_page_state(page, NR_ISOLATED_ANON +
                                 page_is_file_cache(page));
-                if (unlikely(isolated_balloon_page(page)))
+                if (unlikely(isolated_balloon_page(page))) {
                         balloon_page_putback(page);
-                else
+                /*
+                 * We isolated non-lru movable page so here we can use
+                 * __PageMovable because LRU page's mapping cannot have
+                 * PAGE_MAPPING_MOVABLE.
+                 */
+                } else if (unlikely(__PageMovable(page))) {
+                        VM_BUG_ON_PAGE(!PageIsolated(page), page);
+                        lock_page(page);
+                        if (PageMovable(page))
+                                putback_movable_page(page);
+                        else
+                                __ClearPageIsolated(page);
+                        unlock_page(page);
+                        put_page(page);
+                } else {
                         putback_lru_page(page);
+                }
         }
 }
 
@@ -594,7 +685,7 @@ EXPORT_SYMBOL(migrate_page_copy);
  ***********************************************************/
 
 /*
- * Common logic to directly migrate a single page suitable for
+ * Common logic to directly migrate a single LRU page suitable for
  * pages that do not use PagePrivate/PagePrivate2.
  *
  * Pages are locked upon entry and exit.
@@ -757,33 +848,72 @@ static int move_to_new_page(struct page *newpage, struct page *page,
                                 enum migrate_mode mode)
 {
         struct address_space *mapping;
-        int rc;
+        int rc = -EAGAIN;
+        bool is_lru = !__PageMovable(page);
 
         VM_BUG_ON_PAGE(!PageLocked(page), page);
         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
         mapping = page_mapping(page);
-        if (!mapping)
-                rc = migrate_page(mapping, newpage, page, mode);
-        else if (mapping->a_ops->migratepage)
+
+        if (likely(is_lru)) {
+                if (!mapping)
+                        rc = migrate_page(mapping, newpage, page, mode);
+                else if (mapping->a_ops->migratepage)
+                        /*
+                         * Most pages have a mapping and most filesystems
+                         * provide a migratepage callback. Anonymous pages
+                         * are part of swap space which also has its own
+                         * migratepage callback. This is the most common path
+                         * for page migration.
+                         */
+                        rc = mapping->a_ops->migratepage(mapping, newpage,
+                                                        page, mode);
+                else
+                        rc = fallback_migrate_page(mapping, newpage,
+                                                        page, mode);
+        } else {
                 /*
-                 * Most pages have a mapping and most filesystems provide a
-                 * migratepage callback. Anonymous pages are part of swap
-                 * space which also has its own migratepage callback. This
-                 * is the most common path for page migration.
+                 * In case of non-lru page, it could be released after
+                 * isolation step. In that case, we shouldn't try migration.
                  */
-                rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
-        else
-                rc = fallback_migrate_page(mapping, newpage, page, mode);
+                VM_BUG_ON_PAGE(!PageIsolated(page), page);
+                if (!PageMovable(page)) {
+                        rc = MIGRATEPAGE_SUCCESS;
+                        __ClearPageIsolated(page);
+                        goto out;
+                }
+
+                rc = mapping->a_ops->migratepage(mapping, newpage,
+                                                page, mode);
+                WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
+                        !PageIsolated(page));
+        }
 
         /*
          * When successful, old pagecache page->mapping must be cleared before
          * page is freed; but stats require that PageAnon be left as PageAnon.
          */
         if (rc == MIGRATEPAGE_SUCCESS) {
-                if (!PageAnon(page))
+                if (__PageMovable(page)) {
+                        VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+                        /*
+                         * We clear PG_movable under page_lock so any compactor
+                         * cannot try to migrate this page.
+                         */
+                        __ClearPageIsolated(page);
+                }
+
+                /*
+                 * Anonymous and movable page->mapping will be cleard by
+                 * free_pages_prepare so don't reset it here for keeping
+                 * the type to work PageAnon, for example.
+                 */
+                if (!PageMappingFlags(page))
                         page->mapping = NULL;
         }
+out:
         return rc;
 }
 
@@ -793,6 +923,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
         int rc = -EAGAIN;
         int page_was_mapped = 0;
         struct anon_vma *anon_vma = NULL;
+        bool is_lru = !__PageMovable(page);
 
         if (!trylock_page(page)) {
                 if (!force || mode == MIGRATE_ASYNC)
@@ -873,6 +1004,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
                 goto out_unlock_both;
         }
 
+        if (unlikely(!is_lru)) {
+                rc = move_to_new_page(newpage, page, mode);
+                goto out_unlock_both;
+        }
+
         /*
          * Corner case handling:
          * 1. When a new swap-cache page is read into, it is added to the LRU
@@ -922,7 +1058,8 @@ out:
          * list in here.
          */
         if (rc == MIGRATEPAGE_SUCCESS) {
-                if (unlikely(__is_movable_balloon_page(newpage)))
+                if (unlikely(__is_movable_balloon_page(newpage) ||
+                                __PageMovable(newpage)))
                         put_page(newpage);
                 else
                         putback_lru_page(newpage);
@@ -963,6 +1100,12 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
                 /* page was freed from under us. So we are done. */
                 ClearPageActive(page);
                 ClearPageUnevictable(page);
+                if (unlikely(__PageMovable(page))) {
+                        lock_page(page);
+                        if (!PageMovable(page))
+                                __ClearPageIsolated(page);
+                        unlock_page(page);
+                }
                 if (put_new_page)
                         put_new_page(newpage, private);
                 else
@@ -1012,8 +1155,21 @@ out:
                                 num_poisoned_pages_inc();
                 }
         } else {
-                if (rc != -EAGAIN)
-                        putback_lru_page(page);
+                if (rc != -EAGAIN) {
+                        if (likely(!__PageMovable(page))) {
+                                putback_lru_page(page);
+                                goto put_new;
+                        }
+
+                        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