On Thu, 2009-02-12 at 15:15 -0500, Paul Moore wrote:
> On Thursday 12 February 2009 02:50:43 pm Eric Paris wrote:
> > Currently SELinux code has an atomic which was intended to track how many
> > times an avc entry was used and to evict entries when they haven't been
> > used recently. Instead we never let this atomic get above 1 and evict when
> > it is first checked for eviction since it hits zero. This is a total waste
> > of time so I'm completely dropping ae.used.
> >
> > This change resulted in about a 3% faster avc_has_perm_noaudit when running
> > oprofile against a tbench benchmark.
> >
> > Signed-off-by: Eric Paris <eparis@xxxxxxxxxx>
>
> Looks okay to me, I did notice another optimization (see below) that might be
> worth including if you respin the patch.
>
> Reviewed by: Paul Moore <paul.moore@xxxxxx>
>
> > struct avc_node {
> > @@ -321,16 +320,13 @@ static inline int avc_reclaim_node(void)
> >
> > rcu_read_lock();
> > list_for_each_entry(node, &avc_cache.slots[hvalue], list) {
> > - if (atomic_dec_and_test(&node->ae.used)) {
> > - /* Recently Unused */
> > - avc_node_delete(node);
> > - avc_cache_stats_incr(reclaims);
> > - ecx++;
> > - if (ecx >= AVC_CACHE_RECLAIM) {
> > - rcu_read_unlock();
> > - spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
> > - goto out;
> > - }
> > + avc_node_delete(node);
> > + avc_cache_stats_incr(reclaims);
> > + ecx++;
> > + if (ecx >= AVC_CACHE_RECLAIM) {
> > + rcu_read_unlock();
> > + spin_unlock_irqrestore(&avc_cache.slots_lock[hvalue], flags);
> > + goto out;
> > }
> > }
> > rcu_read_unlock();
>
> Not your fault, but in reviewing this code I realized we aren't really using
> the avc_cache.lru_hint atomic either; it looks like it is initialized to zero
> and never changes. With that in mind we could remove the lru_hint field from
> the avc_cache and simplify the above function a tiny bit (no need for hvalue,
> just use zero).
My look says the the hvalue there is computed as:
hvalue = atomic_inc_return(&avc_cache.lru_hint) & (AVC_CACHE_SLOTS - 1);
Which means it is changed....
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