Messages in this thread |  | | Date | Tue, 25 Sep 2001 15:40:23 -0300 (BRT) | From | Marcelo Tosatti <> | Subject | Re: Locking comment on shrink_caches() |
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On Tue, 25 Sep 2001, David S. Miller wrote:
> From: Marcelo Tosatti <marcelo@conectiva.com.br> > Date: Tue, 25 Sep 2001 14:49:40 -0300 (BRT) > > 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() ? > > Marcelo, this is needed because of the spin lock ordering rules. > The pagecache_lock must be obtained before the pagemap_lru_lock > or else deadlock is possible. The spin_trylock is an optimization.
Not, it is not.
We can simply lock the pagecachelock and the pagemap_lru_lock at the beginning of the cleaning function. page_launder() use to do that.
Thats why I asked Andrea if there was long hold times by shrink_caches().
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