On 17.08.21 г. 12:38, Qu Wenruo wrote:

Currently we use u16 bitmap to make 4k sectorsize work for 64K page
size.

But this u16 bitmap is not large enough to contain larger page size like
128K, nor is space efficient for 16K page size.

To handle both cases, here we pack all subpage bitmaps into a larger
bitmap, now btrfs_subpage::bitmaps[] will be the ultimate bitmap for
subpage usage.

Each sub-bitmap will has its start bit number recorded in
btrfs_subpage_info::*_start, and its bitmap length will be recorded in
btrfs_subpage_info::bitmap_nr_bits.

All subpage bitmap operations will be converted from using direct u16
operations to bitmap operations, with above *_start calculated.

For 64K page size with 4K sectorsize, this should not cause much
difference.

While for 16K page size, we will only need 1 unsigned long (u32) to
store all the bitmaps, which saves quite some space.

Furthermore, this allows us to support larger page size like 128K and
258K.

Signed-off-by: Qu Wenruo <redacted>

<snip>

+#define GANG_LOOKUP_SIZE	16
 static struct extent_buffer *get_next_extent_buffer(
 		struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr)
 {
-	struct extent_buffer *gang[BTRFS_SUBPAGE_BITMAP_SIZE];
+	struct extent_buffer *gang[GANG_LOOKUP_SIZE];
 	struct extent_buffer *found = NULL;
 	u64 page_start = page_offset(page);
-	int ret;
-	int i;
+	u64 cur = page_start;
 
 	ASSERT(in_range(bytenr, page_start, PAGE_SIZE));
-	ASSERT(PAGE_SIZE / fs_info->nodesize <= BTRFS_SUBPAGE_BITMAP_SIZE);
 	lockdep_assert_held(&fs_info->buffer_lock);
 
-	ret = radix_tree_gang_lookup(&fs_info->buffer_radix, (void **)gang,
-			bytenr >> fs_info->sectorsize_bits,
-			PAGE_SIZE / fs_info->nodesize);
-	for (i = 0; i < ret; i++) {
-		/* Already beyond page end */
-		if (gang[i]->start >= page_start + PAGE_SIZE)
-			break;
-		/* Found one */
-		if (gang[i]->start >= bytenr) {
-			found = gang[i];
-			break;
+	while (cur < page_start + PAGE_SIZE) {
+		int ret;
+		int i;
+
+		ret = radix_tree_gang_lookup(&fs_info->buffer_radix,
+				(void **)gang, cur >> fs_info->sectorsize_bits,
+				min_t(unsigned int, GANG_LOOKUP_SIZE,
+				      PAGE_SIZE / fs_info->nodesize));
+		if (ret == 0)
+			goto out;
+		for (i = 0; i < ret; i++) {
+			/* Already beyond page end */
+			if (gang[i]->start >= page_start + PAGE_SIZE)

nit: this could be rewritten as (in_range(gang[i]->start, page_start,
PAGE_SIZE)

+				goto out;
+			/* Found one */
+			if (gang[i]->start >= bytenr) {
+				found = gang[i];
+				goto out;
+			}
 		}
+		cur = gang[ret - 1]->start + gang[ret - 1]->len;
 	}
+out:
 	return found;
 }
 

<snip>