On 2017/10/31 21:37, Fan Li wrote:
> In current version, we preserve 8 pages of nat blocks as free nids,
> build bitmaps for it and use them to allocate nids until its number
> drops below NAT_ENTRY_PER_BLOCK.
>
> After that, we have a problem, scan_free_nid_bits will scan the same
> 8 pages trying to find more free nids, but in most cases the free nids
> in these bitmaps are already in free list, scan them won't get us any
> new nids.
> Further more, after scan_free_nid_bits, the search is over if
> nid_cnt[FREE_NID] != 0.
> It causes that we scan the same pages over and over again, yet no new
> free nids are found until nid_cnt[FREE_NID]==0.
>
> This patch mark the range where new free nids could exist and keep scan
> for free nids until nid_cnt[FREE_NID] >= NAT_ENTRY_PER_BLOCK.
> The new vairable first_scan_block marks the start of the range, it's
> initialized with NEW_ADDR, which means all free nids before next_scan_nid
> are already in free list;
> and use next_scan_nid as the end of the range since all free nids which
> are scanned must be smaller next_scan_nid.
>
>
> Signed-off-by: Fan li <fanofcode...@samsung.com>
> ---
> fs/f2fs/f2fs.h | 1 +
> fs/f2fs/node.c | 30 ++++++++++++++++++++++++++----
> 2 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e0ef31c..ae1cf91 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -705,6 +705,7 @@ struct f2fs_nm_info {
> nid_t max_nid; /* maximum possible node ids */
> nid_t available_nids; /* # of available node ids */
> nid_t next_scan_nid; /* the next nid to be scanned */
> + block_t first_scan_block; /* the first NAT block to be scanned */
As we are traveling bitmap, so how about using smaller granularity for tracking
last-scanned-position. like:
unsigned next_bitmap_pos; ?
> unsigned int ram_thresh; /* control the memory footprint */
> unsigned int ra_nid_pages; /* # of nid pages to be readaheaded */
> unsigned int dirty_nats_ratio; /* control dirty nats ratio threshold */
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 3d0d1be..7834097 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1950,10 +1950,23 @@ static void scan_free_nid_bits(struct f2fs_sb_info
> *sbi)
> struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
> struct f2fs_journal *journal = curseg->journal;
> unsigned int i, idx;
> + unsigned int max_blocks = NAT_BLOCK_OFFSET(nm_i->next_scan_nid);
>
> - down_read(&nm_i->nat_tree_lock);
> + /* every free nid in blocks scanned previously is in the free list */
> + if (nm_i->first_scan_block == NEW_ADDR)
How about using nm_i->max_nid as no more free nids in bitmap?
> + return;
>
> - for (i = 0; i < nm_i->nat_blocks; i++) {
> + /*
> + * TODO: "next_scan_nid == 0" means after searching every nat block,
> + * we still can't find enough free nids, there may not be any
> + * more nid left to be found, we should stop at somewhere
> + * instead of going through these all over again.
> + */
> + if (max_blocks == 0)
> + max_blocks = nm_i->nat_blocks;
> +
> + down_read(&nm_i->nat_tree_lock);
> + for (i = nm_i->first_scan_block; i < max_blocks; i++) {
Free nids could be set free after nodes were truncated & checkpoint, if
we start from first_scan_block, we will miss some free nids.
Thanks,
> if (!test_bit_le(i, nm_i->nat_block_bitmap))
> continue;
> if (!nm_i->free_nid_count[i])
> @@ -1967,10 +1980,13 @@ static void scan_free_nid_bits(struct f2fs_sb_info
> *sbi)
> nid = i * NAT_ENTRY_PER_BLOCK + idx;
> add_free_nid(sbi, nid, true);
>
> - if (nm_i->nid_cnt[FREE_NID] >= MAX_FREE_NIDS)
> + if (nm_i->nid_cnt[FREE_NID] >= MAX_FREE_NIDS) {
> + nm_i->first_scan_block = i;
> goto out;
> + }
> }
> }
> + nm_i->first_scan_block = NEW_ADDR;
> out:
> down_read(&curseg->journal_rwsem);
> for (i = 0; i < nats_in_cursum(journal); i++) {
> @@ -2010,7 +2026,7 @@ static void __build_free_nids(struct f2fs_sb_info *sbi,
> bool sync, bool mount)
> /* try to find free nids in free_nid_bitmap */
> scan_free_nid_bits(sbi);
>
> - if (nm_i->nid_cnt[FREE_NID])
> + if (nm_i->nid_cnt[FREE_NID] >= NAT_ENTRY_PER_BLOCK)
> return;
> }
>
> @@ -2163,6 +2179,7 @@ int try_to_free_nids(struct f2fs_sb_info *sbi, int
> nr_shrink)
> struct f2fs_nm_info *nm_i = NM_I(sbi);
> struct free_nid *i, *next;
> int nr = nr_shrink;
> + nid_t min_nid = nm_i->max_nid;
>
> if (nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> return 0;
> @@ -2176,11 +2193,15 @@ int try_to_free_nids(struct f2fs_sb_info *sbi, int
> nr_shrink)
> nm_i->nid_cnt[FREE_NID] <= MAX_FREE_NIDS)
> break;
>
> + if (i->nid < min_nid)
> + min_nid = i->nid;
> __remove_free_nid(sbi, i, FREE_NID);
> kmem_cache_free(free_nid_slab, i);
> nr_shrink--;
> }
> spin_unlock(&nm_i->nid_list_lock);
> + if (min_nid != nm_i->max_nid)
> + nm_i->first_scan_block = NAT_BLOCK_OFFSET(min_nid);
Need to update nm_i->first_scan_block during __flush_nat_entry_set?
Thanks,
> mutex_unlock(&nm_i->build_lock);
>
> return nr - nr_shrink;
> @@ -2674,6 +2695,7 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
> init_rwsem(&nm_i->nat_tree_lock);
>
> nm_i->next_scan_nid = le32_to_cpu(sbi->ckpt->next_free_nid);
> + nm_i->first_scan_block = NEW_ADDR;
> nm_i->bitmap_size = __bitmap_size(sbi, NAT_BITMAP);
> version_bitmap = __bitmap_ptr(sbi, NAT_BITMAP);
> if (!version_bitmap)
>
