[PATCH 09/16] mm: speculative find_get_pages_tag

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: mm-lockless-find_get_pages_tag.patch --]
[-- Type: text/plain, Size: 1904 bytes --]

implement the speculative find_get_pages_tag.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 mm/filemap.c |   42 +++++++++++++++++++++++++++++++++---------
 1 file changed, 33 insertions(+), 9 deletions(-)

Index: linux-2.6-rt/mm/filemap.c
===================================================================
--- linux-2.6-rt.orig/mm/filemap.c	2006-11-30 16:59:17.000000000 +0100
+++ linux-2.6-rt/mm/filemap.c	2006-11-30 17:45:12.000000000 +0100
@@ -838,16 +838,40 @@ unsigned find_get_pages_tag(struct addre
 {
 	unsigned int i;
 	unsigned int ret;
+	unsigned int nr_found;
 
-	read_lock_irq(&mapping->tree_lock);
-	/* TODO: implement lookup_tag_slot and make this lockless */
-	ret = radix_tree_gang_lookup_tag(&mapping->page_tree,
-				(void **)pages, *index, nr_pages, tag);
-	for (i = 0; i < ret; i++)
-		page_cache_get(pages[i]);
-	if (ret)
-		*index = pages[ret - 1]->index + 1;
-	read_unlock_irq(&mapping->tree_lock);
+	rcu_read_lock();
+restart:
+	nr_found = radix_tree_gang_lookup_tag_slot(&mapping->page_tree,
+			(void ***)pages, *index, nr_pages, tag);
+
+	ret = 0;
+	for (i = 0; i < nr_found; i++) {
+		struct page *page;
+repeat:
+		page = radix_tree_deref_slot((void**)pages[i]);
+		if (unlikely(!page))
+			continue;
+		/*
+		 * this can only trigger if nr_found == 1, making livelocks
+		 * a non issue.
+		 */
+		if (unlikely(page == RADIX_TREE_RETRY))
+			goto restart;
+
+		if (!page_cache_get_speculative(page))
+			goto repeat;
+
+		/* Has the page moved? */
+		if (unlikely(page != *((void **)pages[i]))) {
+			page_cache_release(page);
+			goto repeat;
+		}
+
+		pages[ret] = page;
+		ret++;
+	}
+	rcu_read_unlock();
 	return ret;
 }
 

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