The patch titled
Subject: mm: add non-lru movable page support document
has been added to the -mm tree. Its filename is
mm-add-non-lru-movable-page-support-document.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-add-non-lru-movable-page-support-document.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-add-non-lru-movable-page-support-document.patch
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From: Minchan Kim <minchan@xxxxxxxxxx>
Subject: mm: add non-lru movable page support document
Describe what a subsystem should do for non-lru movable page supporting.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Cc: Russ Knize <rknize@xxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx>
Cc: Sangseok Lee <sangseok.lee@xxxxxxx>
Cc: Chan Gyun Jeong <chan.jeong@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: YiPing Xu <xuyiping@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/vfs.txt | 11 ++++
Documentation/vm/page_migration | 69 +++++++++++++++++++++++++++-
2 files changed, 78 insertions(+), 2 deletions(-)
diff -puN Documentation/filesystems/vfs.txt~mm-add-non-lru-movable-page-support-document Documentation/filesystems/vfs.txt
--- a/Documentation/filesystems/vfs.txt~mm-add-non-lru-movable-page-support-document
+++ a/Documentation/filesystems/vfs.txt
@@ -752,12 +752,21 @@ struct address_space_operations {
and transfer data directly between the storage and the
application's address space.
+ isolate_page: Called by the VM when isolating a movable non-lru page.
+ If page is successfully isolated, we should mark the page as
+ PG_isolated via __SetPageIsolated.
+
migrate_page: This is used to compact the physical memory usage.
If the VM wants to relocate a page (maybe off a memory card
that is signalling imminent failure) it will pass a new page
and an old page to this function. migrate_page should
transfer any private data across and update any references
- that it has to the page.
+ that it has to the page. If migrated page is non-lru page,
+ we should clear PG_isolated and PG_movable via __ClearPageIsolated
+ and __ClearPageMovable.
+
+ putback_page: Called by the VM when isolated page's migration fails.
+ We should clear PG_isolated marked in isolated_page function.
launder_page: Called before freeing a page - it writes back the dirty page. To
prevent redirtying the page, it is kept locked during the whole
diff -puN Documentation/vm/page_migration~mm-add-non-lru-movable-page-support-document Documentation/vm/page_migration
--- a/Documentation/vm/page_migration~mm-add-non-lru-movable-page-support-document
+++ a/Documentation/vm/page_migration
@@ -142,5 +142,72 @@ Steps:
20. The new page is moved to the LRU and can be scanned by the swapper
etc again.
-Christoph Lameter, May 8, 2006.
+C. Non-LRU Page migration
+-------------------------
+
+Although original migration aimed for reducing the latency of memory access
+for NUMA, compaction who want to create high-order page is also main customer.
+
+Ppage migration's disadvantage is that it was designed to migrate only
+*LRU* pages. However, there are potential non-lru movable pages which can be
+migrated in system, for example, zsmalloc, virtio-balloon pages.
+For virtio-balloon pages, some parts of migration code path was hooked up
+and added virtio-balloon specific functions to intercept logi.
+It's too specific to one subsystem so other subsystem who want to make
+their pages movable should add own specific hooks in migration path.
+
+To solve such problem, VM supports non-LRU page migration which provides
+generic functions for non-LRU movable pages without needing subsystem
+specific hook in mm/{migrate|compact}.c.
+
+If a subsystem want to make own pages movable, it should mark pages as
+PG_movable via __SetPageMovable. __SetPageMovable needs address_space for
+argument for register functions which will be called by VM.
+
+Three functions in address_space_operation related to non-lru movable page:
+
+ bool (*isolate_page) (struct page *, isolate_mode_t);
+ int (*migratepage) (struct address_space *,
+ struct page *, struct page *, enum migrate_mode);
+ void (*putback_page)(struct page *);
+
+1. Isolation
+
+What VM expected on isolate_page of subsystem is to set PG_isolated flags
+of the page if it was successful. With that, concurrent isolation among
+CPUs skips the isolated page by other CPU earlier. VM calls isolate_page
+under PG_lock of page. If a subsystem cannot isolate the page, it should
+return false.
+2. Migration
+
+After successful isolation, VM calls migratepage. The migratepage's goal is
+to move content of the old page to new page and set up struct page fields
+of new page. If migration is successful, subsystem should release old page's
+refcount to free. Keep in mind that subsystem should clear PG_movable and
+PG_isolated before releasing the refcount. If everything are done, user
+should return MIGRATEPAGE_SUCCESS. If subsystem cannot migrate the page
+at the moment, migratepage can return -EAGAIN. On -EAGAIN, VM will retry page
+migration because VM interprets -EAGAIN as "temporal migration failure".
+
+3. Putback
+
+If migration was unsuccessful, VM calls putback_page. The subsystem should
+insert isolated page to own data structure again if it has. And subsystem
+should clear PG_isolated which was marked in isolation step.
+
+Note about releasing page:
+
+Subsystem can release pages whenever it want but if it releses the page
+which is already isolated, it should clear PG_isolated but doesn't touch
+PG_movable under PG_lock. Instead of it, VM will clear PG_movable after
+his job done. Otherweise, subsystem should clear both page flags before
+releasing the page.
+
+Note about PG_isolated:
+
+PG_isolated check on a page is valid only if the page's flag is already
+set to PG_movable.
+
+Christoph Lameter, May 8, 2006.
+Minchan Kim, Mar 28, 2016.
_
Patches currently in -mm which might be from minchan@xxxxxxxxxx are
zsmalloc-use-first_page-rather-than-page.patch
zsmalloc-clean-up-many-bug_on.patch
zsmalloc-reordering-function-parameter.patch
zsmalloc-remove-unused-pool-param-in-obj_free.patch
mm-use-put_page-to-free-page-instead-of-putback_lru_page.patch
mm-compaction-support-non-lru-movable-page-migration.patch
mm-add-non-lru-movable-page-support-document.patch
mm-balloon-use-general-movable-page-feature-into-balloon.patch
zsmalloc-keep-max_object-in-size_class.patch
zsmalloc-squeeze-inuse-into-page-mapping.patch
zsmalloc-remove-page_mapcount_reset.patch
zsmalloc-squeeze-freelist-into-page-mapping.patch
zsmalloc-move-struct-zs_meta-from-mapping-to-freelist.patch
zsmalloc-factor-page-chain-functionality-out.patch
zsmalloc-separate-free_zspage-from-putback_zspage.patch
zsmalloc-zs_compact-refactoring.patch
zsmalloc-migrate-head-page-of-zspage.patch
zsmalloc-use-single-linked-list-for-page-chain.patch
zsmalloc-migrate-tail-pages-in-zspage.patch
zram-use-__gfp_movable-for-memory-allocation.patch
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