mm: compaction: introduce sync-light migration for use by compaction

This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT
mode that avoids writing back pages to backing storage.  Async compaction
maps to MIGRATE_ASYNC while sync compaction maps to MIGRATE_SYNC_LIGHT.
For other migrate_pages users such as memory hotplug, MIGRATE_SYNC is
used.

This avoids sync compaction stalling for an excessive length of time,
particularly when copying files to a USB stick where there might be a
large number of dirty pages backed by a filesystem that does not support
->writepages.

[aarcange@redhat.com: This patch is heavily based on Andrea's work]
[akpm@linux-foundation.org: fix fs/nfs/write.c build]
[akpm@linux-foundation.org: fix fs/btrfs/disk-io.c build]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andy Isaacson <adi@hexapodia.org>
Cc: Nai Xia <nai.xia@gmail.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 3 insertions, 3 deletions

diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h
index 114398a15830..8102db9b926c 100644
--- a/fs/nfs/internal.h
+++ b/fs/nfs/internal.h
@@ -332,7 +332,7 @@ void nfs_commit_release_pages(struct nfs_write_data *data);
 
 #ifdef CONFIG_MIGRATION
 extern int nfs_migrate_page(struct address_space *,
-                struct page *, struct page *, bool);
+                struct page *, struct page *, enum migrate_mode);
 #else
 #define nfs_migrate_page NULL
 #endif
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 889e98bc5a21..834f0fe96f89 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1688,7 +1688,7 @@ out_error:
 
 #ifdef CONFIG_MIGRATION
 int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
-                struct page *page, bool sync)
+                struct page *page, enum migrate_mode mode)
 {
         /*
          * If PagePrivate is set, then the page is currently associated with
@@ -1703,7 +1703,7 @@ int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
 
         nfs_fscache_release_page(page, GFP_KERNEL);
 
-        return migrate_page(mapping, newpage, page, sync);
+        return migrate_page(mapping, newpage, page, mode);
 }
 #endif