f2fs: avoid unneeded initializing when converting inline dentry

When converting inline dentry, we will zero out target dentry page before
duplicating data of inline dentry into target page, it become overhead
since inline dentry size is not small.

So this patch tries to remove unneeded initializing in the space of target
dentry page.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/inline.c

@@ -384,13 +384,21 @@ static int f2fs_convert_inline_dir(struct inode *dir, struct page *ipage,
 		goto out;
 
 	f2fs_wait_on_page_writeback(page, DATA);
-	zero_user_segment(page, 0, PAGE_CACHE_SIZE);
+	zero_user_segment(page, MAX_INLINE_DATA, PAGE_CACHE_SIZE);
 
 	dentry_blk = kmap_atomic(page);
 
 	/* copy data from inline dentry block to new dentry block */
 	memcpy(dentry_blk->dentry_bitmap, inline_dentry->dentry_bitmap,
 					INLINE_DENTRY_BITMAP_SIZE);
+	memset(dentry_blk->dentry_bitmap + INLINE_DENTRY_BITMAP_SIZE, 0,
+			SIZE_OF_DENTRY_BITMAP - INLINE_DENTRY_BITMAP_SIZE);
+	/*
+	 * we do not need to zero out remainder part of dentry and filename
+	 * field, since we have used bitmap for marking the usage status of
+	 * them, besides, we can also ignore copying/zeroing reserved space
+	 * of dentry block, because them haven't been used so far.
+	 */
 	memcpy(dentry_blk->dentry, inline_dentry->dentry,
 			sizeof(struct f2fs_dir_entry) * NR_INLINE_DENTRY);
 	memcpy(dentry_blk->filename, inline_dentry->filename,