mm: compaction: make isolate_lru_page() filter-aware again

Commit 39deaf85 ("mm: compaction: make isolate_lru_page() filter-aware")
noted that compaction does not migrate dirty or writeback pages and that
is was meaningless to pick the page and re-add it to the LRU list.  This
had to be partially reverted because some dirty pages can be migrated by
compaction without blocking.

This patch updates "mm: compaction: make isolate_lru_page" by skipping
over pages that migration has no possibility of migrating to minimise LRU
disruption.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel<riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
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, 36 insertions, 2 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index d31e64becb38..fb291585e1bf 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -349,6 +349,9 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
                         continue;
                 }
 
+                if (!cc->sync)
+                        mode |= ISOLATE_ASYNC_MIGRATE;
+
                 /* Try isolate the page */
                 if (__isolate_lru_page(page, mode, 0) != 0)
                         continue;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cb68c53db4ec..efbcab1c8f54 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1075,8 +1075,39 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
 
         ret = -EBUSY;
 
-        if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page)))
-                return ret;
+        /*
+         * To minimise LRU disruption, the caller can indicate that it only
+         * wants to isolate pages it will be able to operate on without
+         * blocking - clean pages for the most part.
+         *
+         * ISOLATE_CLEAN means that only clean pages should be isolated. This
+         * is used by reclaim when it is cannot write to backing storage
+         *
+         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
+         * that it is possible to migrate without blocking
+         */
+        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
+                /* All the caller can do on PageWriteback is block */
+                if (PageWriteback(page))
+                        return ret;
+
+                if (PageDirty(page)) {
+                        struct address_space *mapping;
+
+                        /* ISOLATE_CLEAN means only clean pages */
+                        if (mode & ISOLATE_CLEAN)
+                                return ret;
+
+                        /*
+                         * Only pages without mappings or that have a
+                         * ->migratepage callback are possible to migrate
+                         * without blocking
+                         */
+                        mapping = page_mapping(page);
+                        if (mapping && !mapping->a_ops->migratepage)
+                                return ret;
+                }
+        }
 
         if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
                 return ret;