Messages in this thread | | | Date | Thu, 5 Jul 2012 09:26:50 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free() |
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On Sat, 23 Jun 2012, Joonsoo Kim wrote:
> In some case of __slab_free(), we need a lock for manipulating partial list. > If freeing object with a lock is failed, a lock doesn't needed anymore > for some reasons. > > Case 1. prior is NULL, kmem_cache_debug(s) is true > > In this case, another free is occured before our free is succeed. > When slab is full(prior is NULL), only possible operation is slab_free(). > So in this case, we guess another free is occured. > It may make a slab frozen, so lock is not needed anymore.
A free cannot freeze the slab without taking the lock. The taken lock makes sure that the thread that first enters slab_free() will be able to hold back the thread that wants to freeze the slab.
> Case 2. inuse is NULL > > In this case, acquire_slab() is occured before out free is succeed. > We have a last object for slab, so other operation for this slab is > not possible except acquire_slab(). > Acquire_slab() makes a slab frozen, so lock is not needed anymore.
acquire_slab() also requires lock acquisition and would be held of by slab_free holding the lock.
> This also make logic somehow simple that 'was_frozen with a lock' case > is never occured. Remove it.
That is actually interesting and would be a good optimization.
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