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Message-ID: <894561d6-c0eb-4f58-ad3e-96797135e89b@kernel.org>
Date: Mon, 25 Aug 2025 10:51:38 +0800
From: Chao Yu <chao@...nel.org>
To: wangzijie <wangzijie1@...or.com>, jaegeuk@...nel.org
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, bintian.wang@...or.com, feng.han@...or.com
Subject: Re: [f2fs-dev] [PATCH] f2fs: reduce nat_tree_lock hold time when
flush nat entries
On 8/13/25 12:04, wangzijie wrote:
> Sometimes I suffered the nat_tree_lock contention between f2fs_write_checkpoint
> and f2fs_get_node_info. Commit a9419b6("f2fs: do not bother checkpoint by
> f2fs_get_node_info") also mentioned that situation.
>
> My idea is, when flush nat entries, we can use some structures to record nat
> pages we may read, and readahead them before hold nat_tree_lock. Before
> impletement code, I did some survey and found a submittion in community.
>
> Subject: f2fs: use bucket sort to avoid tree lookup and list sort when nat flushing
> Link: https://lore.kernel.org/linux-f2fs-devel/20170520122435.17574-2-houpengyang@huawei.com/
> This patch aims to improve nat entry set sort by using bucket.
> I steal that structure and readahead nat pages contain nat entry set which cannot be moved
> to journal according to dirty nat entry set bucket.
>
> By doing this, I think there are two benefits to reducing nat_tree_lock hold time when
> when flush nat entries.
Zijie,
Can you please figure out some numbers for this patch? something like
checkpoint latency or average or extreme time to grab nat_tree_lock...?
> 1. avoid nat set tree lookup and sort
> 2. readahead nat pages before holding nat_tree_lock
It may cause performance regression if it races w/ drop_caches?
Thanks,
>
> Signed-off-by: wangzijie <wangzijie1@...or.com>
> ---
> fs/f2fs/f2fs.h | 1 +
> fs/f2fs/node.c | 70 ++++++++++++++++++++++++--------------------------
> fs/f2fs/node.h | 2 +-
> 3 files changed, 35 insertions(+), 38 deletions(-)
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 46be75605..b27cc059f 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -975,6 +975,7 @@ struct f2fs_nm_info {
> struct radix_tree_root nat_set_root;/* root of the nat set cache */
> struct f2fs_rwsem nat_tree_lock; /* protect nat entry tree */
> struct list_head nat_entries; /* cached nat entry list (clean) */
> + struct list_head nat_dirty_set[NAT_ENTRY_PER_BLOCK + 1]; /* store dirty nat set */
> spinlock_t nat_list_lock; /* protect clean nat entry list */
> unsigned int nat_cnt[MAX_NAT_STATE]; /* the # of cached nat entries */
> unsigned int nat_blocks; /* # of nat blocks */
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 27743b93e..87c975ee8 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -244,6 +244,12 @@ static void __del_from_nat_cache(struct f2fs_nm_info *nm_i, struct nat_entry *e)
> __free_nat_entry(e);
> }
>
> +static void __relocate_nat_entry_set(struct f2fs_nm_info *nm_i,
> + struct nat_entry_set *set)
> +{
> + list_move_tail(&set->set_list, &nm_i->nat_dirty_set[set->entry_cnt]);
> +}
> +
> static struct nat_entry_set *__grab_nat_entry_set(struct f2fs_nm_info *nm_i,
> struct nat_entry *ne)
> {
> @@ -260,6 +266,7 @@ static struct nat_entry_set *__grab_nat_entry_set(struct f2fs_nm_info *nm_i,
> head->set = set;
> head->entry_cnt = 0;
> f2fs_radix_tree_insert(&nm_i->nat_set_root, set, head);
> + __relocate_nat_entry_set(nm_i, head);
> }
> return head;
> }
> @@ -279,8 +286,10 @@ static void __set_nat_cache_dirty(struct f2fs_nm_info *nm_i,
> * 2. update old block address to new one;
> */
> if (!new_ne && (get_nat_flag(ne, IS_PREALLOC) ||
> - !get_nat_flag(ne, IS_DIRTY)))
> + !get_nat_flag(ne, IS_DIRTY))) {
> head->entry_cnt++;
> + __relocate_nat_entry_set(nm_i, head);
> + }
>
> set_nat_flag(ne, IS_PREALLOC, new_ne);
>
> @@ -309,6 +318,7 @@ static void __clear_nat_cache_dirty(struct f2fs_nm_info *nm_i,
>
> set_nat_flag(ne, IS_DIRTY, false);
> set->entry_cnt--;
> + __relocate_nat_entry_set(nm_i, set);
> nm_i->nat_cnt[DIRTY_NAT]--;
> nm_i->nat_cnt[RECLAIMABLE_NAT]++;
> }
> @@ -2976,24 +2986,6 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
> up_write(&curseg->journal_rwsem);
> }
>
> -static void __adjust_nat_entry_set(struct nat_entry_set *nes,
> - struct list_head *head, int max)
> -{
> - struct nat_entry_set *cur;
> -
> - if (nes->entry_cnt >= max)
> - goto add_out;
> -
> - list_for_each_entry(cur, head, set_list) {
> - if (cur->entry_cnt >= nes->entry_cnt) {
> - list_add(&nes->set_list, cur->set_list.prev);
> - return;
> - }
> - }
> -add_out:
> - list_add_tail(&nes->set_list, head);
> -}
> -
> static void __update_nat_bits(struct f2fs_sb_info *sbi, nid_t start_nid,
> const struct f2fs_nat_block *nat_blk)
> {
> @@ -3095,6 +3087,7 @@ static int __flush_nat_entry_set(struct f2fs_sb_info *sbi,
>
> /* Allow dirty nats by node block allocation in write_begin */
> if (!set->entry_cnt) {
> + list_del(&set->set_list);
> radix_tree_delete(&NM_I(sbi)->nat_set_root, set->set);
> kmem_cache_free(nat_entry_set_slab, set);
> }
> @@ -3109,11 +3102,8 @@ int f2fs_flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> struct f2fs_nm_info *nm_i = NM_I(sbi);
> struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_HOT_DATA);
> struct f2fs_journal *journal = curseg->journal;
> - struct nat_entry_set *setvec[NAT_VEC_SIZE];
> struct nat_entry_set *set, *tmp;
> - unsigned int found;
> - nid_t set_idx = 0;
> - LIST_HEAD(sets);
> + int i;
> int err = 0;
>
> /*
> @@ -3129,6 +3119,16 @@ int f2fs_flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> if (!nm_i->nat_cnt[DIRTY_NAT])
> return 0;
>
> + /* readahead sets which cannot be moved to journal */
> + if (!__has_cursum_space(journal, nm_i->nat_cnt[DIRTY_NAT], NAT_JOURNAL)) {
> + for (i = MAX_NAT_JENTRIES(journal); i <= NAT_ENTRY_PER_BLOCK; i++) {
> + list_for_each_entry_safe(set, tmp, &nm_i->nat_dirty_set[i], set_list) {
> + f2fs_ra_meta_pages(sbi, set->set, 1,
> + META_NAT, true);
> + }
> + }
> + }
> +
> f2fs_down_write(&nm_i->nat_tree_lock);
>
> /*
> @@ -3141,21 +3141,13 @@ int f2fs_flush_nat_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> nm_i->nat_cnt[DIRTY_NAT], NAT_JOURNAL))
> remove_nats_in_journal(sbi);
>
> - while ((found = __gang_lookup_nat_set(nm_i,
> - set_idx, NAT_VEC_SIZE, setvec))) {
> - unsigned idx;
> -
> - set_idx = setvec[found - 1]->set + 1;
> - for (idx = 0; idx < found; idx++)
> - __adjust_nat_entry_set(setvec[idx], &sets,
> - MAX_NAT_JENTRIES(journal));
> - }
> -
> /* flush dirty nats in nat entry set */
> - list_for_each_entry_safe(set, tmp, &sets, set_list) {
> - err = __flush_nat_entry_set(sbi, set, cpc);
> - if (err)
> - break;
> + for (i = 0; i <= NAT_ENTRY_PER_BLOCK; i++) {
> + list_for_each_entry_safe(set, tmp, &nm_i->nat_dirty_set[i], set_list) {
> + err = __flush_nat_entry_set(sbi, set, cpc);
> + if (err)
> + break;
> + }
> }
>
> f2fs_up_write(&nm_i->nat_tree_lock);
> @@ -3249,6 +3241,7 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
> struct f2fs_nm_info *nm_i = NM_I(sbi);
> unsigned char *version_bitmap;
> unsigned int nat_segs;
> + int i;
> int err;
>
> nm_i->nat_blkaddr = le32_to_cpu(sb_raw->nat_blkaddr);
> @@ -3275,6 +3268,9 @@ static int init_node_manager(struct f2fs_sb_info *sbi)
> INIT_LIST_HEAD(&nm_i->nat_entries);
> spin_lock_init(&nm_i->nat_list_lock);
>
> + for (i = 0; i <= NAT_ENTRY_PER_BLOCK; i++)
> + INIT_LIST_HEAD(&nm_i->nat_dirty_set[i]);
> +
> mutex_init(&nm_i->build_lock);
> spin_lock_init(&nm_i->nid_list_lock);
> init_f2fs_rwsem(&nm_i->nat_tree_lock);
> diff --git a/fs/f2fs/node.h b/fs/f2fs/node.h
> index 030390543..d805d4ce7 100644
> --- a/fs/f2fs/node.h
> +++ b/fs/f2fs/node.h
> @@ -158,7 +158,7 @@ enum mem_type {
> };
>
> struct nat_entry_set {
> - struct list_head set_list; /* link with other nat sets */
> + struct list_head set_list; /* link with nat sets which have same entry_cnt */
> struct list_head entry_list; /* link with dirty nat entries */
> nid_t set; /* set number*/
> unsigned int entry_cnt; /* the # of nat entries in set */
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