On Wed, 22 Oct 2008, Miklos Szeredi wrote:
Actually, when debugging is enabled, it's customary to poison the object, for example (see free_debug_processing() in mm/slub.c). So we really can't "easily ensure" that in the allocator unless we by-pass all the current debugging code.
Plus the allocator may be reusing parts of the freed object for a freelist etc even if the object is not poisoned.
Thank you, that does actually answer my question. I would still think it's a good sacrifice to no let the dentries be poisoned for the sake of a simpler dentry defragmenter.
You can simplify defrag by not doing anything in the get() method. That means some of the objects passed to the kick() method may be already have been freed in the interim.
The kick method then must be able to determine if the object has already been freed (or is undergoing freeing) by inspecting the object contents (allocations are held off until kick() is complete). It then needs to free only the objects that are still allocated.
That way you could get to a one stage system.... If the dentry code can give us that then the approach would become much simpler.
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