btrfs: allow extent buffer helpers to skip cross-page handling

Currently btrfs extent buffer helpers are doing all the cross-page
handling, as there is no guarantee that all those eb pages are
contiguous.

However on systems with enough memory, there is a very high chance the
page cache for btree_inode are allocated with physically contiguous
pages.

In that case, we can skip all the complex cross-page handling, thus
speeding up the code.

This patch adds a new member, extent_buffer::addr, which is only set to
non-NULL if all the extent buffer pages are physically contiguous.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -74,15 +74,26 @@ static void btrfs_free_csum_hash(struct btrfs_fs_info *fs_info)
 static void csum_tree_block(struct extent_buffer *buf, u8 *result)
 {
 	struct btrfs_fs_info *fs_info = buf->fs_info;
-	const int num_pages = num_extent_pages(buf);
-	const int first_page_part = min_t(u32, PAGE_SIZE, fs_info->nodesize);
+	int num_pages;
+	u32 first_page_part;
 	SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
 	char *kaddr;
 	int i;
 
 	shash->tfm = fs_info->csum_shash;
 	crypto_shash_init(shash);
-	kaddr = page_address(buf->pages[0]) + offset_in_page(buf->start);
+
+	if (buf->addr) {
+		/* Pages are contiguous, handle them as a big one. */
+		kaddr = buf->addr;
+		first_page_part = fs_info->nodesize;
+		num_pages = 1;
+	} else {
+		kaddr = page_address(buf->pages[0]);
+		first_page_part = min_t(u32, PAGE_SIZE, fs_info->nodesize);
+		num_pages = num_extent_pages(buf);
+	}
+
 	crypto_shash_update(shash, kaddr + BTRFS_CSUM_SIZE,
 			    first_page_part - BTRFS_CSUM_SIZE);
 

fs/btrfs/extent_io.c

@@ -3489,6 +3489,7 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	struct address_space *mapping = fs_info->btree_inode->i_mapping;
 	struct btrfs_subpage *prealloc = NULL;
 	u64 lockdep_owner = owner_root;
+	bool page_contig = true;
 	int uptodate = 1;
 	int ret;
 
@@ -3575,6 +3576,14 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 
 		WARN_ON(btrfs_page_test_dirty(fs_info, p, eb->start, eb->len));
 		eb->pages[i] = p;
+
+		/*
+		 * Check if the current page is physically contiguous with previous eb
+		 * page.
+		 */
+		if (i && eb->pages[i - 1] + 1 != p)
+			page_contig = false;
+
 		if (!btrfs_page_test_uptodate(fs_info, p, eb->start, eb->len))
 			uptodate = 0;
 
@@ -3588,6 +3597,9 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 	}
 	if (uptodate)
 		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+	/* All pages are physically contiguous, can skip cross page handling. */
+	if (page_contig)
+		eb->addr = page_address(eb->pages[0]) + offset_in_page(eb->start);
 again:
 	ret = radix_tree_preload(GFP_NOFS);
 	if (ret) {
@@ -4036,6 +4048,11 @@ void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
 		return;
 	}
 
+	if (eb->addr) {
+		memcpy(dstv, eb->addr + start, len);
+		return;
+	}
+
 	offset = get_eb_offset_in_page(eb, start);
 
 	while (len > 0) {
@@ -4067,6 +4084,12 @@ int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
 	WARN_ON(start > eb->len);
 	WARN_ON(start + len > eb->start + eb->len);
 
+	if (eb->addr) {
+		if (copy_to_user_nofault(dstv, eb->addr + start, len))
+			ret = -EFAULT;
+		return ret;
+	}
+
 	offset = get_eb_offset_in_page(eb, start);
 
 	while (len > 0) {
@@ -4102,6 +4125,9 @@ int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
 	if (check_eb_range(eb, start, len))
 		return -EINVAL;
 
+	if (eb->addr)
+		return memcmp(ptrv, eb->addr + start, len);
+
 	offset = get_eb_offset_in_page(eb, start);
 
 	while (len > 0) {
@@ -4169,6 +4195,14 @@ static void __write_extent_buffer(const struct extent_buffer *eb,
 	if (check_eb_range(eb, start, len))
 		return;
 
+	if (eb->addr) {
+		if (use_memmove)
+			memmove(eb->addr + start, srcv, len);
+		else
+			memcpy(eb->addr + start, srcv, len);
+		return;
+	}
+
 	offset = get_eb_offset_in_page(eb, start);
 
 	while (len > 0) {
@@ -4201,6 +4235,11 @@ static void memset_extent_buffer(const struct extent_buffer *eb, int c,
 {
 	unsigned long cur = start;
 
+	if (eb->addr) {
+		memset(eb->addr + start, c, len);
+		return;
+	}
+
 	while (cur < start + len) {
 		unsigned long index = get_eb_page_index(cur);
 		unsigned int offset = get_eb_offset_in_page(eb, cur);
@@ -4428,6 +4467,16 @@ void memcpy_extent_buffer(const struct extent_buffer *dst,
 	    check_eb_range(dst, src_offset, len))
 		return;
 
+	if (dst->addr) {
+		const bool use_memmove = areas_overlap(src_offset, dst_offset, len);
+
+		if (use_memmove)
+			memmove(dst->addr + dst_offset, dst->addr + src_offset, len);
+		else
+			memcpy(dst->addr + dst_offset, dst->addr + src_offset, len);
+		return;
+	}
+
 	while (cur_off < len) {
 		unsigned long cur_src = cur_off + src_offset;
 		unsigned long pg_index = get_eb_page_index(cur_src);
@@ -4460,6 +4509,11 @@ void memmove_extent_buffer(const struct extent_buffer *dst,
 		return;
 	}
 
+	if (dst->addr) {
+		memmove(dst->addr + dst_offset, dst->addr + src_offset, len);
+		return;
+	}
+
 	while (len > 0) {
 		unsigned long src_i;
 		size_t cur;

fs/btrfs/extent_io.h

@@ -78,6 +78,13 @@ struct extent_buffer {
 	unsigned long len;
 	unsigned long bflags;
 	struct btrfs_fs_info *fs_info;
+
+	/*
+	 * The address where the eb can be accessed without any cross-page handling.
+	 * This can be NULL if not possible.
+	 */
+	void *addr;
+
 	spinlock_t refs_lock;
 	atomic_t refs;
 	int read_mirror;