[patch 07/12] Slab defragmentation: Support for buffer_head defrag

Christoph Lameter
2007-07-08T03:05:45Z

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Limited defragmentation support for buffer heads. Simply try to free the
buffers in a sparsely populated slab page.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
fs/buffer.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 65 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc6-mm1/fs/buffer.c
===================================================================
--- linux-2.6.22-rc6-mm1.orig/fs/buffer.c 2007-07-04 11:14:01.000000000 -0700
+++ linux-2.6.22-rc6-mm1/fs/buffer.c 2007-07-04 17:23:02.000000000 -0700
@@ -3078,12 +3078,75 @@ static int buffer_cpu_notify(struct noti
return NOTIFY_OK;
}

+/*
+ * Get references on buffers.
+ *
+ * We obtain references on the page that uses the buffer. v[i] will point to
+ * the corresponding page after get_buffers() is through.
+ *
+ * We are safe from the underlying page being removed simply by doing
+ * a get_page_unless_zero. The buffer head removal may race at will.
+ * try_to_free_buffes will later take appropriate locks to remove the
+ * buffers if they are still there.
+ *
+ * TODO: Write out dirty buffers to increase the chance of kick_buffers
+ * to be successful.
+ */
+static void *get_buffers(struct kmem_cache *s, int nr, void **v)
+{
+ struct page *page;
+ struct buffer_head *bh;
+ int i;
+
+ for (i = 0; i < nr; i++) {
+ bh = v[i];
+ page = bh->b_page;
+ if (page && PagePrivate(page) && get_page_unless_zero(page))
+ v[i] = page;
+ else
+ v[i] = NULL;
+ }
+ return NULL;
+}
+
+/*
+ * Despite its name: kick_buffers operates on a list of pointers to
+ * page structs that was setup by get_buffer
+ */
+static void kick_buffers(struct kmem_cache *s, int nr, void **v,
+ void *private)
+{
+ struct page *page;
+ int i;
+
+ for (i = 0; i < nr; i++) {
+ page = v[i];
+
+ if (!page)
+ continue;
+
+ if (!TestSetPageLocked(page)) {
+ if (PagePrivate(page))
+ try_to_free_buffers(page);
+ unlock_page(page);
+ }
+ put_page(page);
+ }
+}
+
+static struct kmem_cache_ops buffer_head_kmem_cache_ops = {
+ .get = get_buffers,
+ .kick = kick_buffers,
+};
+
+
void __init buffer_init(void)
{
int nrpages;

- bh_cachep = KMEM_CACHE(buffer_head,
- SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD);
+ bh_cachep = KMEM_CACHE_OPS(buffer_head,
+ SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD,
+ &buffer_head_kmem_cache_ops);

/*
* Limit the bh occupancy to 10% of ZONE_NORMAL

--