Hi, Matthew, Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > On Mon, Apr 22, 2024 at 03:54:58PM +0800, Huang, Ying wrote: >> Is it possible to add "start_offset" support in xarray, so "index" >> will subtract "start_offset" before looking up / inserting? > > We kind of have that with XA_FLAGS_ZERO_BUSY which is used for > XA_FLAGS_ALLOC1. But that's just one bit for the entry at 0. We could > generalise it, but then we'd have to store that somewhere and there's > no obvious good place to store it that wouldn't enlarge struct xarray, > which I'd be reluctant to do. > >> Is it possible to use multiple range locks to protect one xarray to >> improve the lock scalability? This is why we have multiple "struct >> address_space" for one swap device. And, we may have same lock >> contention issue for large files too. > > It's something I've considered. The issue is search marks. If we delete > an entry, we may have to walk all the way up the xarray clearing bits as > we go and I'd rather not grab a lock at each level. There's a convenient > 4 byte hole between nr_values and parent where we could put it. > > Oh, another issue is that we use i_pages.xa_lock to synchronise > address_space.nrpages, so I'm not sure that a per-node lock will help. Thanks for looking at this. > But I'm conscious that there are workloads which show contention on > xa_lock as their limiting factor, so I'm open to ideas to improve all > these things. I have no idea so far because my very limited knowledge about xarray. -- Best Regards, Huang, Ying
