Locking comment on shrink_caches()

[Marcelo Tosatti]

Andrea, 

Do you really need to do this ? 

                if (unlikely(!spin_trylock(&pagecache_lock))) {
                        /* we hold the page lock so the page cannot go away from under us */
                        spin_unlock(&pagemap_lru_lock);

                        spin_lock(&pagecache_lock);
                        spin_lock(&pagemap_lru_lock);
                }

Have you actually seen bad hold times of pagecache_lock by
shrink_caches() ? 

Its just that I prefer clear locking without those "tricks". (easier to
understand and harder to miss subtle details)