Btrfs: reduce extent_state lock contention for metadata

For metadata buffers that don't straddle pages (all of them), btrfs
can safely use the page uptodate bits and extent_buffer uptodate bit
instead of needing to use the extent_state tree.

This greatly reduces contention on the state tree lock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 5392c3b..7b60f62 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3268,6 +3268,22 @@ int set_extent_buffer_dirty(struct extent_io_tree *tree,
        return was_dirty;
 }
 
+static int __eb_straddles_pages(u64 start, u64 len)
+{
+       if (len < PAGE_CACHE_SIZE)
+               return 1;
+       if (start & (PAGE_CACHE_SIZE - 1))
+               return 1;
+       if ((start + len) & (PAGE_CACHE_SIZE - 1))
+               return 1;
+       return 0;
+}
+
+static int eb_straddles_pages(struct extent_buffer *eb)
+{
+       return __eb_straddles_pages(eb->start, eb->len);
+}
+
 int clear_extent_buffer_uptodate(struct extent_io_tree *tree,
                                struct extent_buffer *eb,
                                struct extent_state **cached_state)
@@ -3279,8 +3295,10 @@ int clear_extent_buffer_uptodate(struct extent_io_tree *tree,
        num_pages = num_extent_pages(eb->start, eb->len);
        clear_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
 
-       clear_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
-                             cached_state, GFP_NOFS);
+       if (eb_straddles_pages(eb)) {
+               clear_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
+                                     cached_state, GFP_NOFS);
+       }
        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if (page)
@@ -3298,8 +3316,10 @@ int set_extent_buffer_uptodate(struct extent_io_tree *tree,
 
        num_pages = num_extent_pages(eb->start, eb->len);
 
-       set_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
-                           NULL, GFP_NOFS);
+       if (eb_straddles_pages(eb)) {
+               set_extent_uptodate(tree, eb->start, eb->start + eb->len - 1,
+                                   NULL, GFP_NOFS);
+       }
        for (i = 0; i < num_pages; i++) {
                page = extent_buffer_page(eb, i);
                if ((i == 0 && (eb->start & (PAGE_CACHE_SIZE - 1))) ||
@@ -3322,9 +3342,12 @@ int extent_range_uptodate(struct extent_io_tree *tree,
        int uptodate;
        unsigned long index;
 
-       ret = test_range_bit(tree, start, end, EXTENT_UPTODATE, 1, NULL);
-       if (ret)
-               return 1;
+       if (__eb_straddles_pages(start, end - start + 1)) {
+               ret = test_range_bit(tree, start, end,
+                                    EXTENT_UPTODATE, 1, NULL);
+               if (ret)
+                       return 1;
+       }
        while (start <= end) {
                index = start >> PAGE_CACHE_SHIFT;
                page = find_get_page(tree->mapping, index);
@@ -3352,10 +3375,12 @@ int extent_buffer_uptodate(struct extent_io_tree *tree,
        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 1;
 
-       ret = test_range_bit(tree, eb->start, eb->start + eb->len - 1,
-                          EXTENT_UPTODATE, 1, cached_state);
-       if (ret)
-               return ret;
+       if (eb_straddles_pages(eb)) {
+               ret = test_range_bit(tree, eb->start, eb->start + eb->len - 1,
+                                  EXTENT_UPTODATE, 1, cached_state);
+               if (ret)
+                       return ret;
+       }
 
        num_pages = num_extent_pages(eb->start, eb->len);
        for (i = 0; i < num_pages; i++) {
@@ -3388,9 +3413,11 @@ int read_extent_buffer_pages(struct extent_io_tree *tree,
        if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
                return 0;
 
-       if (test_range_bit(tree, eb->start, eb->start + eb->len - 1,
-                          EXTENT_UPTODATE, 1, NULL)) {
-               return 0;
+       if (eb_straddles_pages(eb)) {
+               if (test_range_bit(tree, eb->start, eb->start + eb->len - 1,
+                                  EXTENT_UPTODATE, 1, NULL)) {
+                       return 0;
+               }
        }
 
        if (start) {