f2fs: don't use GFP_ZERO for page caches

Related to https://lkml.org/lkml/2018/4/8/661

Sometimes, we need to write meta data to new allocated block address,
then we will allocate a zeroed page in inner inode's address space, and
fill partial data in it, and leave other place with zero value which means
some fields are initial status.

There are two inner inodes (meta inode and node inode) setting __GFP_ZERO,
I have just checked them, for both of them, we can avoid using __GFP_ZERO,
and do initialization by ourselves to avoid unneeded/redundant zeroing
from mm.

Cc: <stable@vger.kernel.org>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/checkpoint.c

@@ -100,8 +100,10 @@ static struct page *__get_meta_page(struct f2fs_sb_info *sbi, pgoff_t index,
 	 * readonly and make sure do not write checkpoint with non-uptodate
 	 * meta page.
 	 */
-	if (unlikely(!PageUptodate(page)))
+	if (unlikely(!PageUptodate(page))) {
+		memset(page_address(page), 0, PAGE_SIZE);
 		f2fs_stop_checkpoint(sbi, false);
+	}
 out:
 	return page;
 }

fs/f2fs/inode.c

@@ -320,10 +320,10 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
 make_now:
 	if (ino == F2FS_NODE_INO(sbi)) {
 		inode->i_mapping->a_ops = &f2fs_node_aops;
-		mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO);
+		mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS);
 	} else if (ino == F2FS_META_INO(sbi)) {
 		inode->i_mapping->a_ops = &f2fs_meta_aops;
-		mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO);
+		mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS);
 	} else if (S_ISREG(inode->i_mode)) {
 		inode->i_op = &f2fs_file_inode_operations;
 		inode->i_fop = &f2fs_file_operations;

fs/f2fs/segment.c

@@ -1979,6 +1979,7 @@ static void write_current_sum_page(struct f2fs_sb_info *sbi,
 	struct f2fs_summary_block *dst;
 
 	dst = (struct f2fs_summary_block *)page_address(page);
+	memset(dst, 0, PAGE_SIZE);
 
 	mutex_lock(&curseg->curseg_mutex);
 
@@ -3133,6 +3134,7 @@ static void write_compacted_summaries(struct f2fs_sb_info *sbi, block_t blkaddr)
 
 	page = grab_meta_page(sbi, blkaddr++);
 	kaddr = (unsigned char *)page_address(page);
+	memset(kaddr, 0, PAGE_SIZE);
 
 	/* Step 1: write nat cache */
 	seg_i = CURSEG_I(sbi, CURSEG_HOT_DATA);
@@ -3157,6 +3159,7 @@ static void write_compacted_summaries(struct f2fs_sb_info *sbi, block_t blkaddr)
 			if (!page) {
 				page = grab_meta_page(sbi, blkaddr++);
 				kaddr = (unsigned char *)page_address(page);
+				memset(kaddr, 0, PAGE_SIZE);
 				written_size = 0;
 			}
 			summary = (struct f2fs_summary *)(kaddr + written_size);

fs/f2fs/segment.h

@@ -375,6 +375,7 @@ static inline void seg_info_to_sit_page(struct f2fs_sb_info *sbi,
 	int i;
 
 	raw_sit = (struct f2fs_sit_block *)page_address(page);
+	memset(raw_sit, 0, PAGE_SIZE);
 	for (i = 0; i < end - start; i++) {
 		rs = &raw_sit->entries[i];
 		se = get_seg_entry(sbi, start + i);