為了儲存current segment的summary資訊，f2fs在do_checkpoint的時候會呼叫會呼叫write_data_summaries和write_node_summaries將其sumamries資訊寫到page cache中然後隨後同步到磁碟中，其中write_node_summaries也是隻有在umount和fastboot的情況下才會呼叫。我們可以看到write_data_summaries中有著兩種方式進行存放，所以本文就這兩種方式進行講述。

void write_data_summaries(struct f2fs_sb_info *sbi, block_t start_blk)
{
	if (is_set_ckpt_flags(sbi, CP_COMPACT_SUM_FLAG))
		write_compacted_summaries(sbi, start_blk);
	else
		write_normal_summaries(sbi, start_blk, CURSEG_HOT_DATA);
}
 

    這兩種方式分別是write_compacted_summaries和write_normal_summaries，下面就這兩種方式進行詳細的講述。

static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
{
	...

	data_sum_blocks = npages_for_summary_flush(sbi, false);
	spin_lock(&sbi->cp_lock);
	if (data_sum_blocks < NR_CURSEG_DATA_TYPE)
		__set_ckpt_flags(ckpt, CP_COMPACT_SUM_FLAG);
	else
		__clear_ckpt_flags(ckpt, CP_COMPACT_SUM_FLAG);
	spin_unlock(&sbi->cp_lock);

	...

}
 

int npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra)
{
	int valid_sum_count = 0;
	int i, sum_in_page;

	for (i = CURSEG_HOT_DATA; i <= CURSEG_COLD_DATA; i++) {
		if (sbi->ckpt->alloc_type[i] == SSR)
			valid_sum_count += sbi->blocks_per_seg;
		else {
			if (for_ra)
				valid_sum_count += le16_to_cpu(
					F2FS_CKPT(sbi)->cur_data_blkoff[i]);
			else
				valid_sum_count += curseg_blkoff(sbi, i);
		}
	}

	sum_in_page = (PAGE_SIZE - 2 * SUM_JOURNAL_SIZE - SUM_FOOTER_SIZE) / SUMMARY_SIZE;
	if (valid_sum_count <= sum_in_page)
		return 1;
	else if ((valid_sum_count - sum_in_page) <= (PAGE_SIZE - SUM_FOOTER_SIZE) / SUMMARY_SIZE)
		return 2;
	return 3;
}
 

static void write_compacted_summaries(struct f2fs_sb_info *sbi, block_t blkaddr)
{
	struct page *page;
	unsigned char *kaddr;
	struct f2fs_summary *summary;
	struct curseg_info *seg_i;
	int written_size = 0;
	int i, j;

	page = grab_meta_page(sbi, blkaddr++);
	kaddr = (unsigned char *)page_address(page);

	seg_i = CURSEG_I(sbi, CURSEG_HOT_DATA);
	memcpy(kaddr, seg_i->journal, SUM_JOURNAL_SIZE);
	written_size += SUM_JOURNAL_SIZE;

	seg_i = CURSEG_I(sbi, CURSEG_COLD_DATA);
	memcpy(kaddr + written_size, seg_i->journal, SUM_JOURNAL_SIZE);
	written_size += SUM_JOURNAL_SIZE;

	for (i = CURSEG_HOT_DATA; i <= CURSEG_COLD_DATA; i++) {
		unsigned short blkoff;
		seg_i = CURSEG_I(sbi, i);
		if (sbi->ckpt->alloc_type[i] == SSR)
			blkoff = sbi->blocks_per_seg;
		else
			blkoff = curseg_blkoff(sbi, i);

		for (j = 0; j < blkoff; j++) {
			if (!page) {
				page = grab_meta_page(sbi, blkaddr++);
				kaddr = (unsigned char *)page_address(page);
				written_size = 0;
			}
			summary = (struct f2fs_summary *)(kaddr + written_size);
			*summary = seg_i->sum_blk->entries[j];
			written_size += SUMMARY_SIZE;

			if (written_size + SUMMARY_SIZE <= PAGE_SIZE - SUM_FOOTER_SIZE)
				continue;

			set_page_dirty(page);
			f2fs_put_page(page, 1);
			page = NULL;
		}
	}
	if (page) {
		set_page_dirty(page);
		f2fs_put_page(page, 1);
	}
}

static void write_normal_summaries(struct f2fs_sb_info *sbi, block_t blkaddr, int type)
{
	int i, end;
	if (IS_DATASEG(type))
		end = type + NR_CURSEG_DATA_TYPE;
	else
		end = type + NR_CURSEG_NODE_TYPE;

	for (i = type; i < end; i++)
		write_current_sum_page(sbi, i, blkaddr + (i - type));
}

static void write_current_sum_page(struct f2fs_sb_info *sbi, int type, block_t blk_addr)
{
	struct curseg_info *curseg = CURSEG_I(sbi, type);
	struct page *page = grab_meta_page(sbi, blk_addr);
	struct f2fs_summary_block *src = curseg->sum_blk;
	struct f2fs_summary_block *dst;

	dst = (struct f2fs_summary_block *)page_address(page);

	mutex_lock(&curseg->curseg_mutex);

	down_read(&curseg->journal_rwsem);
	memcpy(&dst->journal, curseg->journal, SUM_JOURNAL_SIZE);
	up_read(&curseg->journal_rwsem);

	memcpy(dst->entries, src->entries, SUM_ENTRY_SIZE);
	memcpy(&dst->footer, &src->footer, SUM_FOOTER_SIZE);

	mutex_unlock(&curseg->curseg_mutex);

	set_page_dirty(page);
	f2fs_put_page(page, 1);
}