Re: [PATCH 07/10 v7] sunrpc: Switch to using list_head instead single list

[NeilBrown <neilb@suse.com>]

On Sat, 11 Jul 2015 20:50:26 +0800 Kinglong Mee <kinglongmee@gmail.com>
wrote:

> Switch using list_head for cache_head in cache_detail,
> it is useful of remove an cache_head entry directly from cache_detail.
> 
> v7, same as v6.
> 
> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
> ---
>  include/linux/sunrpc/cache.h |  4 +--
>  net/sunrpc/cache.c           | 74 ++++++++++++++++++++++++--------------------
>  2 files changed, 43 insertions(+), 35 deletions(-)
> 
> diff --git a/include/linux/sunrpc/cache.h b/include/linux/sunrpc/cache.h
> index 04ee5a2..ecc0ff6 100644
> --- a/include/linux/sunrpc/cache.h
> +++ b/include/linux/sunrpc/cache.h
> @@ -46,7 +46,7 @@
>   * 
>   */
>  struct cache_head {
> -	struct cache_head * next;
> +	struct list_head	cache_list;
>  	time_t		expiry_time;	/* After time time, don't use the data */
>  	time_t		last_refresh;   /* If CACHE_PENDING, this is when upcall 
>  					 * was sent, else this is when update was received
> @@ -73,7 +73,7 @@ struct cache_detail_pipefs {
>  struct cache_detail {
>  	struct module *		owner;
>  	int			hash_size;
> -	struct cache_head **	hash_table;
> +	struct list_head *	hash_table;
>  	rwlock_t		hash_lock;

Given that these lists are chains in a hash table, it would make more
sense to use hlist_head rather than list_head.  They are designed for
exactly that purpose - and are smaller.

Actually, I'd really like to see hlist_bl_head used - so there was one
bit-spin-lock per chain, and use RCU for protecting searches.
However that would have to be left for later - no point delaying this
patch set for some minor performance gains.

But as you need to change this, I think it would be best to change to
hlist_head.

By the way, I see lots of nice clean-ups in this series.  Thanks!

NeilBrown


>  
>  	atomic_t		inuse; /* active user-space update or lookup */
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index 673c2fa..ad2155c 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -44,7 +44,7 @@ static void cache_revisit_request(struct cache_head *item);
>  static void cache_init(struct cache_head *h)
>  {
>  	time_t now = seconds_since_boot();
> -	h->next = NULL;
> +	INIT_LIST_HEAD(&h->cache_list);
>  	h->flags = 0;
>  	kref_init(&h->ref);
>  	h->expiry_time = now + CACHE_NEW_EXPIRY;
> @@ -54,15 +54,16 @@ static void cache_init(struct cache_head *h)
>  struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
>  				       struct cache_head *key, int hash)
>  {
> -	struct cache_head **head,  **hp;
>  	struct cache_head *new = NULL, *freeme = NULL;
> +	struct cache_head *tmp;
> +	struct list_head *head, *pos, *tpos;
>  
>  	head = &detail->hash_table[hash];
>  
>  	read_lock(&detail->hash_lock);
>  
> -	for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
> -		struct cache_head *tmp = *hp;
> +	list_for_each_safe(pos, tpos, head) {
> +		tmp = list_entry(pos, struct cache_head, cache_list);
>  		if (detail->match(tmp, key)) {
>  			if (cache_is_expired(detail, tmp))
>  				/* This entry is expired, we will discard it. */
> @@ -88,12 +89,11 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
>  	write_lock(&detail->hash_lock);
>  
>  	/* check if entry appeared while we slept */
> -	for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
> -		struct cache_head *tmp = *hp;
> +	list_for_each_safe(pos, tpos, head) {
> +		tmp = list_entry(pos, struct cache_head, cache_list);
>  		if (detail->match(tmp, key)) {
>  			if (cache_is_expired(detail, tmp)) {
> -				*hp = tmp->next;
> -				tmp->next = NULL;
> +				list_del_init(&tmp->cache_list);
>  				detail->entries --;
>  				freeme = tmp;
>  				break;
> @@ -104,8 +104,8 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
>  			return tmp;
>  		}
>  	}
> -	new->next = *head;
> -	*head = new;
> +
> +	list_add(&new->cache_list, head);
>  	detail->entries++;
>  	cache_get(new);
>  	write_unlock(&detail->hash_lock);
> @@ -143,7 +143,6 @@ struct cache_head *sunrpc_cache_update(struct cache_detail *detail,
>  	 * If 'old' is not VALID, we update it directly,
>  	 * otherwise we need to replace it
>  	 */
> -	struct cache_head **head;
>  	struct cache_head *tmp;
>  
>  	if (!test_bit(CACHE_VALID, &old->flags)) {
> @@ -168,15 +167,13 @@ struct cache_head *sunrpc_cache_update(struct cache_detail *detail,
>  	}
>  	cache_init(tmp);
>  	detail->init(tmp, old);
> -	head = &detail->hash_table[hash];
>  
>  	write_lock(&detail->hash_lock);
>  	if (test_bit(CACHE_NEGATIVE, &new->flags))
>  		set_bit(CACHE_NEGATIVE, &tmp->flags);
>  	else
>  		detail->update(tmp, new);
> -	tmp->next = *head;
> -	*head = tmp;
> +	list_add(&tmp->cache_list, &detail->hash_table[hash]);
>  	detail->entries++;
>  	cache_get(tmp);
>  	cache_fresh_locked(tmp, new->expiry_time);
> @@ -416,42 +413,44 @@ static int cache_clean(void)
>  	/* find a non-empty bucket in the table */
>  	while (current_detail &&
>  	       current_index < current_detail->hash_size &&
> -	       current_detail->hash_table[current_index] == NULL)
> +	       list_empty(&current_detail->hash_table[current_index]))
>  		current_index++;
>  
>  	/* find a cleanable entry in the bucket and clean it, or set to next bucket */
>  
>  	if (current_detail && current_index < current_detail->hash_size) {
> -		struct cache_head *ch, **cp;
> +		struct cache_head *ch = NULL, *putme = NULL;
> +		struct list_head *head, *pos, *tpos;
>  		struct cache_detail *d;
>  
>  		write_lock(&current_detail->hash_lock);
>  
>  		/* Ok, now to clean this strand */
>  
> -		cp = & current_detail->hash_table[current_index];
> -		for (ch = *cp ; ch ; cp = & ch->next, ch = *cp) {
> +		head = &current_detail->hash_table[current_index];
> +		list_for_each_safe(pos, tpos, head) {
> +			ch = list_entry(pos, struct cache_head, cache_list);
>  			if (current_detail->nextcheck > ch->expiry_time)
>  				current_detail->nextcheck = ch->expiry_time+1;
>  			if (!cache_is_expired(current_detail, ch))
>  				continue;
>  
> -			*cp = ch->next;
> -			ch->next = NULL;
> +			list_del_init(pos);
>  			current_detail->entries--;
> +			putme = ch;
>  			rv = 1;
>  			break;
>  		}
>  
>  		write_unlock(&current_detail->hash_lock);
>  		d = current_detail;
> -		if (!ch)
> +		if (!putme)
>  			current_index ++;
>  		spin_unlock(&cache_list_lock);
> -		if (ch) {
> -			set_bit(CACHE_CLEANED, &ch->flags);
> -			cache_fresh_unlocked(ch, d);
> -			cache_put(ch, d);
> +		if (putme) {
> +			set_bit(CACHE_CLEANED, &putme->flags);
> +			cache_fresh_unlocked(putme, d);
> +			cache_put(putme, d);
>  		}
>  	} else
>  		spin_unlock(&cache_list_lock);
> @@ -1277,6 +1276,7 @@ void *cache_seq_start(struct seq_file *m, loff_t *pos)
>  	unsigned int hash, entry;
>  	struct cache_head *ch;
>  	struct cache_detail *cd = m->private;
> +	struct list_head *ptr, *tptr;
>  
>  	read_lock(&cd->hash_lock);
>  	if (!n--)
> @@ -1284,19 +1284,22 @@ void *cache_seq_start(struct seq_file *m, loff_t *pos)
>  	hash = n >> 32;
>  	entry = n & ((1LL<<32) - 1);
>  
> -	for (ch=cd->hash_table[hash]; ch; ch=ch->next)
> +	list_for_each_safe(ptr, tptr, &cd->hash_table[hash]) {
> +		ch = list_entry(ptr, struct cache_head, cache_list);
>  		if (!entry--)
>  			return ch;
> +	}
>  	n &= ~((1LL<<32) - 1);
>  	do {
>  		hash++;
>  		n += 1LL<<32;
>  	} while(hash < cd->hash_size &&
> -		cd->hash_table[hash]==NULL);
> +		list_empty(&cd->hash_table[hash]));
>  	if (hash >= cd->hash_size)
>  		return NULL;
>  	*pos = n+1;
> -	return cd->hash_table[hash];
> +	return list_first_entry_or_null(&cd->hash_table[hash],
> +					struct cache_head, cache_list);
>  }
>  EXPORT_SYMBOL_GPL(cache_seq_start);
>  
> @@ -1308,23 +1311,24 @@ void *cache_seq_next(struct seq_file *m, void *p, loff_t *pos)
>  
>  	if (p == SEQ_START_TOKEN)
>  		hash = 0;
> -	else if (ch->next == NULL) {
> +	else if (list_is_last(&ch->cache_list, &cd->hash_table[hash])) {
>  		hash++;
>  		*pos += 1LL<<32;
>  	} else {
>  		++*pos;
> -		return ch->next;
> +		return list_next_entry(ch, cache_list);
>  	}
>  	*pos &= ~((1LL<<32) - 1);
>  	while (hash < cd->hash_size &&
> -	       cd->hash_table[hash] == NULL) {
> +	       list_empty(&cd->hash_table[hash])) {
>  		hash++;
>  		*pos += 1LL<<32;
>  	}
>  	if (hash >= cd->hash_size)
>  		return NULL;
>  	++*pos;
> -	return cd->hash_table[hash];
> +	return list_first_entry_or_null(&cd->hash_table[hash],
> +					struct cache_head, cache_list);
>  }
>  EXPORT_SYMBOL_GPL(cache_seq_next);
>  
> @@ -1666,17 +1670,21 @@ EXPORT_SYMBOL_GPL(cache_unregister_net);
>  struct cache_detail *cache_create_net(struct cache_detail *tmpl, struct net *net)
>  {
>  	struct cache_detail *cd;
> +	int i;
>  
>  	cd = kmemdup(tmpl, sizeof(struct cache_detail), GFP_KERNEL);
>  	if (cd == NULL)
>  		return ERR_PTR(-ENOMEM);
>  
> -	cd->hash_table = kzalloc(cd->hash_size * sizeof(struct cache_head *),
> +	cd->hash_table = kzalloc(cd->hash_size * sizeof(struct list_head),
>  				 GFP_KERNEL);
>  	if (cd->hash_table == NULL) {
>  		kfree(cd);
>  		return ERR_PTR(-ENOMEM);
>  	}
> +
> +	for (i = 0; i < cd->hash_size; i++)
> +		INIT_LIST_HEAD(&cd->hash_table[i]);
>  	cd->net = net;
>  	return cd;
>  }