On Thu, 10 Jan 2008, Matt Mackall wrote: > Here I'm going to differ with you. The premises of the SLAB concept > (from the original paper) are: > > a) fragmentation of conventional allocators gets worse over time
Even fragmentation of SLAB/SLUB gets worses over time. That is why we need a defrag solution. > b) grouping objects of the same -type- (not size) together should mean > they have similar lifetimes and thereby keep fragmentation low I agree that is crap. The lifetimes argument is mostly only exploitable in benchmarks. That is why SLUB just groups them by size if possible. > d) constructors and destructors are cache-friendly I agree. Crap too. We removed the destructors. The constructors are needed so that objects in slab pages always have a definite state. That is f.e. necessary for slab defragmentation because it has to be able to inspect an object at an arbitrary time and either remove it or move it to another slab page. Constructors also make sense because the initialization of a cache object may be expensive. Initializing list heads and spinlocks can take some code and that code can be omitted if objects have a definite state when they are free. We saw that when measuring the buffer_head constructors effect on performance. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
