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Subject[PATCH 2/3] f2fs: refactor __build_free_nids
Date
Previously, in __build_free_nids we try to load bitmap from
next_scan_nid pointed NAT block, but actually, due to nat_bits
bitmap, current NAT blocks readed can be already ran out, so
it makes __build_free_nids low efficiency.

This patch refactors __build_free_nids a bit to search
nat_block_bitmap first to find out which NAT blocks have not been
loaded yet, and then do loading bitmaps.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
fs/f2fs/node.c | 54 ++++++++++++++++++++++++++++++++++--------------------
1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 4c758747980c..fb52622727ea 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1865,13 +1865,13 @@ static void scan_curseg_cache(struct f2fs_sb_info *sbi, nid_t start_nid,
up_read(&curseg->journal_rwsem);
}

-static void scan_nat_page(struct f2fs_sb_info *sbi, nid_t nid)
+static void scan_nat_page(struct f2fs_sb_info *sbi, unsigned int nat_ofs)
{
struct f2fs_nm_info *nm_i = NM_I(sbi);
struct page *page;
struct f2fs_nat_block *nat_blk;
block_t blk_addr;
- unsigned int nat_ofs = NAT_BLOCK_OFFSET(nid);
+ nid_t nid = nat_ofs * NAT_ENTRY_PER_BLOCK;
nid_t start_nid = nid;
int i;

@@ -1935,37 +1935,51 @@ static nid_t lookup_free_nid_bitmap(struct f2fs_sb_info *sbi)
static void __build_free_nids(struct f2fs_sb_info *sbi, bool mount)
{
struct f2fs_nm_info *nm_i = NM_I(sbi);
- int i = 0;
- nid_t nid = nm_i->next_scan_nid;
+ unsigned int pos, start, end, max_cnt = nm_i->nat_blocks;
+ bool sync_ra = true;

- if (unlikely(nid >= nm_i->max_nid))
- nid = 0;
+ if (unlikely(nm_i->next_scan_nid >= nm_i->max_nid))
+ nm_i->next_scan_nid = 0;

/* Enough entries */
if (!mount && nm_i->available_free_nids >= NAT_ENTRY_PER_BLOCK)
return;

- /* readahead nat pages to be scanned */
- ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), FREE_NID_PAGES,
- META_NAT, true);
+ start = NAT_BLOCK_OFFSET(nm_i->next_scan_nid);

- down_read(&nm_i->nat_tree_lock);
+readahead:
+ /* search unloaded bitmap in range of [start, max] */
+ pos = find_next_zero_bit_le(nm_i->nat_block_bitmap, max_cnt, start);
+ if (pos >= max_cnt) {
+ if (!start)
+ return;
+ /* search unloaded bitmap in range of [0, start] */
+ pos = find_next_zero_bit_le(nm_i->nat_block_bitmap, start, 0);
+ if (pos >= start)
+ return;
+ }

- do {
- scan_nat_page(sbi, nid);
+ end = find_next_bit_le(nm_i->nat_block_bitmap, max_cnt, pos);
+ end = min(end, start + FREE_NID_PAGES);

- nid += (NAT_ENTRY_PER_BLOCK - (nid % NAT_ENTRY_PER_BLOCK));
- if (unlikely(nid >= nm_i->max_nid))
- nid = 0;
- } while (++i < FREE_NID_PAGES);
+ /* readahead nat pages to be scanned */
+ ra_meta_pages(sbi, pos, end - pos, META_NAT, sync_ra);

- /* go to the next free nat pages to find free nids abundantly */
- nm_i->next_scan_nid = nid;
+ if (!sync_ra)
+ return;

+ down_read(&nm_i->nat_tree_lock);
+ for (; pos < end; pos++)
+ scan_nat_page(sbi, pos);
up_read(&nm_i->nat_tree_lock);

- ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nm_i->next_scan_nid),
- nm_i->ra_nid_pages, META_NAT, false);
+ /* go to the next free nat pages to find free nids abundantly */
+ nm_i->next_scan_nid = end * NAT_ENTRY_PER_BLOCK;
+
+ /* do async readahead for continual nid allocation */
+ start = NAT_BLOCK_OFFSET(nm_i->next_scan_nid);
+ sync_ra = false;
+ goto readahead;
}

void build_free_nids(struct f2fs_sb_info *sbi, bool mount)
--
2.15.0.55.gc2ece9dc4de6
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