[PATCH 06/14] btrfs: extent_io: support subpage for extent buffer page release

From: Qu Wenruo <wqu@suse.com>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH 06/14] btrfs: extent_io: support subpage for extent buffer page release
Date: Wed, 18 Nov 2020 16:53:11 +0800	[thread overview]
Message-ID: <20201118085319.56668-7-wqu@suse.com> (raw)
In-Reply-To: <20201118085319.56668-1-wqu@suse.com>

In btrfs_release_extent_buffer_pages(), we need to add extra handling
for subpage.

To do so, introduce a new helper, detach_extent_buffer_page(), to do
different handling for regular and subpage cases.

For subpage case, the new trick is to clear the range of current extent
buffer, and detach page private if and only if we're the last tree block
of the page.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 70 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 53 insertions(+), 17 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f424a26a695e..090acf0e6a59 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4999,25 +4999,12 @@ int extent_buffer_under_io(const struct extent_buffer *eb)
 		test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
 }
 
-/*
- * Release all pages attached to the extent buffer.
- */
-static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
+static void detach_extent_buffer_page(struct extent_buffer *eb,
+				      struct page *page)
 {
-	int i;
-	int num_pages;
-	int mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
-
-	BUG_ON(extent_buffer_under_io(eb));
-
-	num_pages = num_extent_pages(eb);
-	for (i = 0; i < num_pages; i++) {
-		struct page *page = eb->pages[i];
+	struct btrfs_fs_info *fs_info = eb->fs_info;
 
-		if (!page)
-			continue;
-		if (mapped)
-			spin_lock(&page->mapping->private_lock);
+	if (!btrfs_is_subpage(fs_info)) {
 		/*
 		 * We do this since we'll remove the pages after we've
 		 * removed the eb from the radix tree, so we could race
@@ -5036,6 +5023,55 @@ static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
 			 */
 			detach_page_private(page);
 		}
+	}
+
+	/*
+	 * For subpage case, clear the range in tree_block_bitmap,
+	 * and if we're the last one, detach private completely.
+	 */
+	if (PagePrivate(page)) {
+		struct btrfs_subpage *subpage;
+		int start = (eb->start - page_offset(page)) >>
+			    fs_info->sectorsize_bits;
+		int nbits = (eb->len) >> fs_info->sectorsize_bits;
+		bool last = false;
+
+		ASSERT(page_offset(page) <= eb->start &&
+		       eb->start + eb->len <= page_offset(page) + PAGE_SIZE);
+
+		subpage = (struct btrfs_subpage *)page->private;
+		spin_lock_bh(&subpage->lock);
+		bitmap_clear(subpage->tree_block_bitmap, start, nbits);
+		if (bitmap_empty(subpage->tree_block_bitmap,
+				 BTRFS_SUBPAGE_BITMAP_SIZE))
+			last = true;
+		spin_unlock_bh(&subpage->lock);
+		if (last)
+			btrfs_detach_subpage(fs_info, page);
+	}
+}
+
+/*
+ * Release all pages attached to the extent buffer.
+ */
+static void btrfs_release_extent_buffer_pages(struct extent_buffer *eb)
+{
+	int i;
+	int num_pages;
+	int mapped = !test_bit(EXTENT_BUFFER_UNMAPPED, &eb->bflags);
+
+	ASSERT(!extent_buffer_under_io(eb));
+
+	num_pages = num_extent_pages(eb);
+	for (i = 0; i < num_pages; i++) {
+		struct page *page = eb->pages[i];
+
+		if (!page)
+			continue;
+		if (mapped)
+			spin_lock(&page->mapping->private_lock);
+
+		detach_extent_buffer_page(eb, page);
 
 		if (mapped)
 			spin_unlock(&page->mapping->private_lock);
-- 
2.29.2

