radix-tree: delete radix_tree_range_tag_if_tagged()

This is an exceptionally complicated function with just one caller
(tag_pages_for_writeback).  We devote a large portion of the runtime of
the test suite to testing this one function which has one caller.  By
introducing the new function radix_tree_iter_tag_set(), we can eliminate
all of the complexity while keeping the performance.  The caller can now
use a fairly standard radix_tree_for_each() loop, and it doesn't need to
worry about tricksy things like 'start' wrapping.

The test suite continues to spend a large amount of time investigating
this function, but now it's testing the underlying primitives such as
radix_tree_iter_resume() and the radix_tree_for_each_tagged() iterator
which are also used by other parts of the kernel.

Link: http://lkml.kernel.org/r/1480369871-5271-57-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 52e2f8e3b472..290e8b7d3181 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2106,18 +2106,26 @@ void tag_pages_for_writeback(struct address_space *mapping,
                              pgoff_t start, pgoff_t end)
 {
 #define WRITEBACK_TAG_BATCH 4096
-        unsigned long tagged;
-
-        do {
-                spin_lock_irq(&mapping->tree_lock);
-                tagged = radix_tree_range_tag_if_tagged(&mapping->page_tree,
-                                &start, end, WRITEBACK_TAG_BATCH,
-                                PAGECACHE_TAG_DIRTY, PAGECACHE_TAG_TOWRITE);
+        unsigned long tagged = 0;
+        struct radix_tree_iter iter;
+        void **slot;
+
+        spin_lock_irq(&mapping->tree_lock);
+        radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, start,
+                                                        PAGECACHE_TAG_DIRTY) {
+                if (iter.index > end)
+                        break;
+                radix_tree_iter_tag_set(&mapping->page_tree, &iter,
+                                                        PAGECACHE_TAG_TOWRITE);
+                tagged++;
+                if ((tagged % WRITEBACK_TAG_BATCH) != 0)
+                        continue;
+                slot = radix_tree_iter_resume(slot, &iter);
                 spin_unlock_irq(&mapping->tree_lock);
-                WARN_ON_ONCE(tagged > WRITEBACK_TAG_BATCH);
                 cond_resched();
-                /* We check 'start' to handle wrapping when end == ~0UL */
-        } while (tagged >= WRITEBACK_TAG_BATCH && start);
+                spin_lock_irq(&mapping->tree_lock);
+        }
+        spin_unlock_irq(&mapping->tree_lock);
 }
 EXPORT_SYMBOL(tag_pages_for_writeback);