Messages in this thread | | | From | "Christian Ehrhardt" <> | Date | Thu, 5 Sep 2002 14:34:13 +0200 | Subject | Re: [RFC] Alternative raceless page free |
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On Thu, Sep 05, 2002 at 06:42:12AM +0200, Daniel Phillips wrote: > I have a slight preference for the extra-lru-count version, because of the > trylock in page_cache_release. This means that nobody will have to spin when > shrink_cache is active. Instead, freed pages that collide with the lru lock > can just be left on the lru list to be picked up efficiently later. The > trylock also allows the lru lock to be acquired speculatively from interrupt > context, without a requirement that lru lock holders disable interrupts. > Both versions are provably correct, modulo implementation gaffs. > > The linked patch defaults to atomic_dec_and_lock version. To change to > the extra count version, define LRU_PLUS_CACHE as 2 instead of 1. > > Christian, can you please run this one through your race detector?
I don't see a priciple problem with this approach (except that there may be architectures that don't have cmpxchg or similar). But this hunk
@@ -455,7 +458,7 @@ } else { /* failed to drop the buffers so stop here */ UnlockPage(page); - page_cache_release(page); + put_page(page);
spin_lock(&pagemap_lru_lock); continue;
looks a bit suspicious. put_page is not allowed if the page is still on the lru and there is no other reference to it. As we don't hold any locks between UnlockPage and put_page there is no formal guarantee that the above condition is met. I don't have another path that could race with this one though and chances are that there actually is none.
regards Christian
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