Re: Locking comment on shrink_caches()

David S. Miller (
Tue, 25 Sep 2001 12:57:58 -0700 (PDT)

From: Marcelo Tosatti <>
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 */


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.

Franks a lot,
David S. Miller
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