On 3/16/21 11:42 AM, Xunlei Pang wrote: > On 3/16/21 2:49 AM, Vlastimil Babka wrote: >> On 3/9/21 4:25 PM, Xunlei Pang wrote: >>> count_partial() can hold n->list_lock spinlock for quite long, which >>> makes much trouble to the system. This series eliminate this problem. >> >> Before I check the details, I have two high-level comments: >> >> - patch 1 introduces some counting scheme that patch 4 then changes, could we do >> this in one step to avoid the churn? >> >> - the series addresses the concern that spinlock is being held, but doesn't >> address the fact that counting partial per-node slabs is not nearly enough if we >> want accurate <active_objs> in /proc/slabinfo because there are also percpu >> slabs and per-cpu partial slabs, where we don't track the free objects at all. >> So after this series while the readers of /proc/slabinfo won't block the >> spinlock, they will get the same garbage data as before. So Christoph is not >> wrong to say that we can just report active_objs == num_objs and it won't >> actually break any ABI. > > If maintainers don't mind this inaccuracy which I also doubt its > importance, then it becomes easy. For fear that some people who really > cares, introducing an extra config(default-off) for it would be a good > option. Great. >> At the same time somebody might actually want accurate object statistics at the >> expense of peak performance, and it would be nice to give them such option in >> SLUB. Right now we don't provide this accuracy even with CONFIG_SLUB_STATS, >> although that option provides many additional tuning stats, with additional >> overhead. >> So my proposal would be a new config for "accurate active objects" (or just tie >> it to CONFIG_SLUB_DEBUG?) that would extend the approach of percpu counters in >> patch 4 to all alloc/free, so that it includes percpu slabs. Without this config >> enabled, let's just report active_objs == num_objs. > For percpu slabs, the numbers can be retrieved from the existing > slub_percpu_partial()->pobjects, looks no need extra work. Hm, unfortunately it's not that simple, the number there is a snapshot that can become wildly inacurate afterwards.
