On Mon, Sep 20, 2021 at 01:09:38AM +0000, Hyeonggon Yoo wrote: > Hello Matthew, Thanks to give me a comment! I appreciate it. > > On Sun, Sep 19, 2021 at 08:17:44PM +0100, Matthew Wilcox wrote: > > On Sun, Sep 19, 2021 at 04:42:39PM +0000, Hyeonggon Yoo wrote: > > > It is just simple proof of concept, and not ready for submission yet. > > > There can be wrong code (like wrong gfp flags, or wrong error handling, > > > etc) it is just simple proof of concept. I want comment from you. > > > > Have you read: > > > > https://www.usenix.org/legacy/event/usenix01/full_papers/bonwick/bonwick_html/ > > The relevant part of that paper is section 3, magazines. We should have > > low and high water marks for number of objects > > I haven't read that before, but after reading it seems not different from > SLAB's percpu queuing. > > > and we should allocate > > from / free to the slab allocator in batches. Slab has bulk alloc/free > > APIs already. > > > > There's kmem_cache_alloc_{bulk,free} functions for bulk > allocation. But it's designed for large number of allocation > to reduce locking cost, not for percpu lockless allocation. What I'm saying is that rather than a linked list of objects, we should have an array of, say, 15 pointers per CPU (and a count of how many allocations we have). If we are trying to allocate and have no objects, call kmem_cache_alloc_bulk() for 8 objects. If we are trying to free and have 15 objects already, call kmem_cache_free_bulk() for the last 8 objects and set the number of allocated objects to 7. (maybe 8 and 15 are the wrong numbers. this is just an example) > Yeah, we can implement lockless cache using kmem_cache_alloc_{bulk, free} > but kmem_cache_alloc_{free,bulk} is not enough. > > > I'd rather see this be part of the slab allocator than a separate API. > > And I disagree on this. for because most of situation, we cannot > allocate without lock, it is special case for IO polling. > > To make it as part of slab allocator, we need to modify existing data > structure. But making it part of slab allocator will be waste of memory > because most of them are not using this. Oh, it would have to be an option. Maybe as a new slab_flags_t flag. Or maybe a kmem_cache_alloc_percpu_lockless().
