[patch 5/9] mm: lockless probe

Nick Piggin
2007-04-12T12:45:33Z

Probing pages and radix_tree_tagged are lockless operations with the
lockless radix-tree. Convert these users to RCU locking rather than
using tree_lock.

Signed-off-by: Nick Piggin <npiggin@suse.de>

Index: linux-2.6/drivers/mtd/devices/block2mtd.c
===================================================================
--- linux-2.6.orig/drivers/mtd/devices/block2mtd.c
+++ linux-2.6/drivers/mtd/devices/block2mtd.c
@@ -59,28 +59,27 @@ static void cache_readahead(struct addre

end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);

- read_lock_irq(&mapping->tree_lock);
for (i = 0; i < PAGE_READAHEAD; i++) {
pagei = index + i;
if (pagei > end_index) {
INFO("Overrun end of disk in cache readahead\n");
break;
}
+ /* Don't need mapping->tree_lock - lookup can be racy */
+ rcu_read_lock();
page = radix_tree_lookup(&mapping->page_tree, pagei);
+ rcu_read_unlock();
if (page && (!i))
break;
if (page)
continue;
- read_unlock_irq(&mapping->tree_lock);
page = page_cache_alloc_cold(mapping);
- read_lock_irq(&mapping->tree_lock);
if (!page)
break;
page->index = pagei;
list_add(&page->lru, &page_pool);
ret++;
}
- read_unlock_irq(&mapping->tree_lock);
if (ret)
read_cache_pages(mapping, &page_pool, filler, NULL);
}
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c
+++ linux-2.6/mm/page-writeback.c
@@ -965,17 +965,15 @@ int test_set_page_writeback(struct page
EXPORT_SYMBOL(test_set_page_writeback);

/*
- * Return true if any of the pages in the mapping are marged with the
+ * Return true if any of the pages in the mapping are marked with the
* passed tag.
*/
int mapping_tagged(struct address_space *mapping, int tag)
{
- unsigned long flags;
int ret;
-
- read_lock_irqsave(&mapping->tree_lock, flags);
+ rcu_read_lock();
ret = radix_tree_tagged(&mapping->page_tree, tag);
- read_unlock_irqrestore(&mapping->tree_lock, flags);
+ rcu_read_unlock();
return ret;
}
EXPORT_SYMBOL(mapping_tagged);
Index: linux-2.6/mm/readahead.c
===================================================================
--- linux-2.6.orig/mm/readahead.c
+++ linux-2.6/mm/readahead.c
@@ -281,27 +281,25 @@ __do_page_cache_readahead(struct address
/*
* Preallocate as many pages as we will need.
*/
- read_lock_irq(&mapping->tree_lock);
for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
pgoff_t page_offset = offset + page_idx;

if (page_offset > end_index)
break;

+ rcu_read_lock();
page = radix_tree_lookup(&mapping->page_tree, page_offset);
+ rcu_read_unlock();
if (page)
continue;

- read_unlock_irq(&mapping->tree_lock);
page = page_cache_alloc_cold(mapping);
- read_lock_irq(&mapping->tree_lock);
if (!page)
break;
page->index = page_offset;
list_add(&page->lru, &page_pool);
ret++;
}
- read_unlock_irq(&mapping->tree_lock);

/*
* Now start the IO. We ignore I/O errors - if the page is not