On (24/02/27 16:16), Chengming Zhou wrote: > On 2024/2/27 15:52, Sergey Senozhatsky wrote: > > On (24/02/27 03:00), chengming.zhou@xxxxxxxxx wrote: > >> > >> We only need to save the position (pfn + obj_idx) in the handle, don't > >> need to save tag bit in handle. So one more bit can be used as obj_idx. > > > > [..] > > > >> mm/zsmalloc: don't need to save tag bit in handle > > > > Does this mean "don't need to reserve LSB for tag"? > The head of object still need to reverve LSB, to save (handle | OBJ_ALLOCATED_TAG), > only the handle doesn't need to reserve LSB, which save (pfn | obj_idx). Correct. > > We still save allocated tag in the handle, that's what > > > > handle |= OBJ_ALLOCATED_TAG; > > Yes, this result will be saved in the head of each allocated object. Right, that's what I was talking about. > >> Actually, the tag bit is only useful in zspage's memory space, to tell > >> if an object is allocated or not. > > > > I'm not completely sure if I follow this sentence. > > What I mean is that only the head of each allocated object need to reverve LSB, > which is used to check if allocated or not. > > handle address -> handle (pfn + obj_idx) -> object: (handle | tag), real_object start > > I'm not sure if this makes it clearer? Yes, thanks. I think separating handle and object header in the commit message will be helpful.
