On 3/1/24 19:53, Roman Gushchin wrote: > On Fri, Mar 01, 2024 at 09:51:18AM -0800, Linus Torvalds wrote: >> What I *think* I'd want for this case is >> >> (a) allow the accounting to go over by a bit >> >> (b) make sure there's a cheap way to ask (before) about "did we go >> over the limit" >> >> IOW, the accounting never needed to be byte-accurate to begin with, >> and making it fail (cheaply and early) on the next file allocation is >> fine. >> >> Just make it really cheap. Can we do that? >> >> For example, maybe don't bother with the whole "bytes and pages" >> stuff. Just a simple "are we more than one page over?" kind of >> question. Without the 'stock_lock' mess for sub-page bytes etc >> >> How would that look? Would it result in something that can be done >> cheaply without locking and atomics and without excessive pointer >> indirection through many levels of memcg data structures? > > I think it's possible and I'm currently looking into batching charge, > objcg refcnt management and vmstats using per-task caching. It should > speed up things for the majority of allocations. > For allocations from an irq context and targeted allocations > (where the target memcg != memcg of the current task) we'd probably need to > keep the old scheme. I hope to post some patches relatively soon. Do you think this will work on top of this series, i.e. patches 1+2 could be eventually put to slab/for-next after the merge window, or would it interfere with your changes? > I tried to optimize the current implementation but failed to get any > significant gains. It seems that the overhead is very evenly spread across > objcg pointer access, charge management, objcg refcnt management and vmstats. > > Thanks!
