Re: [RFC][PATCH 2/7] UBC: core (structures, API)

[Kirill Korotaev]

Oleg,

> > +struct user_beancounter *beancounter_findcreate(uid_t uid,
> > +		struct user_beancounter *p, int mask)
> > +{
> > +	struct user_beancounter *new_ub, *ub, *tmpl_ub;
> > +	unsigned long flags;
> > +	struct hlist_head *slot;
> > +	struct hlist_node *pos;
> > +
> > +	if (mask & UB_LOOKUP_SUB) {
> > +		WARN_ON(p == NULL);
> > +		tmpl_ub = &default_subbeancounter;
> > +		slot = &ub_hash[ub_subhash_fun(p, uid)];
> > +	} else {
> > +		WARN_ON(p != NULL);
> > +		tmpl_ub = &default_beancounter;
> > +		slot = &ub_hash[ub_hash_fun(uid)];
> > +	}
> > +	new_ub = NULL;
> > +
> > +retry:
> > +	spin_lock_irqsave(&ub_hash_lock, flags);
> > +	hlist_for_each_entry (ub, pos, slot, hash)
> > +		if (ub->ub_uid == uid && ub->parent == p)
> > +			break;
> > +
> > +	if (pos != NULL) {
> > +		get_beancounter(ub);
> > +		spin_unlock_irqrestore(&ub_hash_lock, flags);
> > +
> > +		if (new_ub != NULL) {
> > +			put_beancounter(new_ub->parent);
>
> 					^^^^^^^^^^^^^^
>
> Stupid question: why ->parent can't be NULL ? (without UB_LOOKUP_SUB).
oh, good catch. We removed the check for NULL in put_beancounter() for cleanup,
but didn't notice this place. Thanks!

> > +	if (mask & UB_ALLOC_ATOMIC) {
> > +		new_ub = kmem_cache_alloc(ub_cachep, GFP_ATOMIC);
> > +		if (new_ub == NULL)
> > +			goto out_unlock;
> > +
> > +		memcpy(new_ub, tmpl_ub, sizeof(*new_ub));
> > +		init_beancounter_struct(new_ub, uid);
> > +		if (p)
> > +			new_ub->parent = get_beancounter(p);
> > +		goto out_install;
> > +	}
> > +
> > +	spin_unlock_irqrestore(&ub_hash_lock, flags);
> > +
> > +	new_ub = kmem_cache_alloc(ub_cachep, GFP_KERNEL);
>
>
> beancounter_findcreate() is not time critical, yes? Isn't it better
> to kill 'if (mask & UB_ALLOC_ATOMIC) { ... }' and just do
>
> 	new_ub = kmem_cache_alloc(ub_cachep,
> 		UB_ALLOC_ATOMIC ? GFP_ATOMIC : GFP_KERNEL);
>
> after spin_unlock(&ub_hash_lock) ?
ok, will do. Thanks for comments!

Kirill
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