[PATCH 43/62] brd: Convert to XArray

Matthew Wilcox
2017-11-22T21:13:51Z

Convert brd_pages from a radix tree to an XArray. Simpler and smaller
code; in particular another user of radix_tree_preload is eliminated.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
drivers/block/brd.c | 87 ++++++++++++++---------------------------------------
1 file changed, 23 insertions(+), 64 deletions(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 8028a3a7e7fd..c9fda03810ea 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -17,7 +17,7 @@
#include <linux/bio.h>
#include <linux/highmem.h>
#include <linux/mutex.h>
-#include <linux/radix-tree.h>
+#include <linux/xarray.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
@@ -29,9 +29,9 @@
#define PAGE_SECTORS (1 << PAGE_SECTORS_SHIFT)

/*
- * Each block ramdisk device has a radix_tree brd_pages of pages that stores
- * the pages containing the block device's contents. A brd page's ->index is
- * its offset in PAGE_SIZE units. This is similar to, but in no way connected
+ * Each block ramdisk device has an xarray brd_pages that stores the pages
+ * containing the block device's contents. A brd page's ->index is its
+ * offset in PAGE_SIZE units. This is similar to, but in no way connected
* with, the kernel's pagecache or buffer cache (which sit above our block
* device).
*/
@@ -41,13 +41,7 @@ struct brd_device {
struct request_queue *brd_queue;
struct gendisk *brd_disk;
struct list_head brd_list;
-
- /*
- * Backing store of pages and lock to protect it. This is the contents
- * of the block device.
- */
- spinlock_t brd_lock;
- struct radix_tree_root brd_pages;
+ struct xarray brd_pages;
};

/*
@@ -62,17 +56,9 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
* The page lifetime is protected by the fact that we have opened the
* device node -- brd pages will never be deleted under us, so we
* don't need any further locking or refcounting.
- *
- * This is strictly true for the radix-tree nodes as well (ie. we
- * don't actually need the rcu_read_lock()), however that is not a
- * documented feature of the radix-tree API so it is better to be
- * safe here (we don't have total exclusion from radix tree updates
- * here, only deletes).
*/
- rcu_read_lock();
idx = sector >> PAGE_SECTORS_SHIFT; /* sector to page index */
- page = radix_tree_lookup(&brd->brd_pages, idx);
- rcu_read_unlock();
+ page = xa_load(&brd->brd_pages, idx);

BUG_ON(page && page->index != idx);

@@ -87,7 +73,7 @@ static struct page *brd_lookup_page(struct brd_device *brd, sector_t sector)
static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
{
pgoff_t idx;
- struct page *page;
+ struct page *curr, *page;
gfp_t gfp_flags;

page = brd_lookup_page(brd, sector);
@@ -108,62 +94,36 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
if (!page)
return NULL;

- if (radix_tree_preload(GFP_NOIO)) {
- __free_page(page);
- return NULL;
- }
-
- spin_lock(&brd->brd_lock);
idx = sector >> PAGE_SECTORS_SHIFT;
page->index = idx;
- if (radix_tree_insert(&brd->brd_pages, idx, page)) {
+ curr = xa_cmpxchg(&brd->brd_pages, idx, NULL, page, GFP_NOIO);
+ if (curr) {
__free_page(page);
- page = radix_tree_lookup(&brd->brd_pages, idx);
+ page = curr;
BUG_ON(!page);
BUG_ON(page->index != idx);
}
- spin_unlock(&brd->brd_lock);
-
- radix_tree_preload_end();

return page;
}

/*
- * Free all backing store pages and radix tree. This must only be called when
+ * Free all backing store pages and xarray. This must only be called when
* there are no other users of the device.
*/
-#define FREE_BATCH 16
static void brd_free_pages(struct brd_device *brd)
{
- unsigned long pos = 0;
- struct page *pages[FREE_BATCH];
- int nr_pages;
-
- do {
- int i;
-
- nr_pages = radix_tree_gang_lookup(&brd->brd_pages,
- (void **)pages, pos, FREE_BATCH);
-
- for (i = 0; i < nr_pages; i++) {
- void *ret;
-
- BUG_ON(pages[i]->index < pos);
- pos = pages[i]->index;
- ret = radix_tree_delete(&brd->brd_pages, pos);
- BUG_ON(!ret || ret != pages[i]);
- __free_page(pages[i]);
- }
-
- pos++;
-
- /*
- * This assumes radix_tree_gang_lookup always returns as
- * many pages as possible. If the radix-tree code changes,
- * so will this have to.
- */
- } while (nr_pages == FREE_BATCH);
+ XA_STATE(xas, 0);
+ struct page *page;
+
+ /* lockdep can't know there are no other users */
+ xa_lock(&brd->brd_pages);
+ xas_for_each(&brd->brd_pages, &xas, page, ULONG_MAX) {
+ BUG_ON(page->index != xas.xa_index);
+ __free_page(page);
+ xas_store(&brd->brd_pages, &xas, NULL);
+ }
+ xa_unlock(&brd->brd_pages);
}

/*
@@ -373,8 +333,7 @@ static struct brd_device *brd_alloc(int i)
if (!brd)
goto out;
brd->brd_number = i;
- spin_lock_init(&brd->brd_lock);
- INIT_RADIX_TREE(&brd->brd_pages, GFP_ATOMIC);
+ xa_init(&brd->brd_pages);

brd->brd_queue = blk_alloc_queue(GFP_KERNEL);
if (!brd->brd_queue)
--
2.15.0