On Thu, 14 Nov 2024, Johannes Weiner wrote: > > > > The reason that I opted not to include a breakdown of each hugetlb > > > > size in memory.stat is only because I wanted to keep the addition that > > > > this patch makes as minimal as possible, while still addressing > > > > the goal of bridging the gap between memory.stat and memory.current. > > > > Users who are curious about this breakdown can see how much memory > > > > is used by each hugetlb size by enabling the hugetlb controller as well. > > > > > > > > > > While the patch may be minimal, this is solidifying a kernel API that > > > users will start to count on. Users who may be interested in their > > > hugetlb usage may not have control over the configuration of their kernel? > > > > > > Does it make sense to provide a breakdown in memory.stat so that users can > > > differentiate between mapping one 1GB hugetlb page and 512 2MB hugetlb > > > pages, which are different global resources? > > > > > > > It's true that this is the case as well for total hugeltb usage, but > > > > I felt that not including hugetlb memory usage in memory.stat when it > > > > is accounted by memory.current would cause confusion for the users > > > > not being able to see that memory.current = sum of memory.stat. On the > > > > other hand, seeing the breakdown of how much each hugetlb size felt more > > > > like an optimization, and not a solution that bridges a confusion. > > > > > > > > > > If broken down into hugetlb_2048kB and hugetlb_1048576kB on x86, for > > > example, users could still do sum of memory.stat, no?> > > > > > > > Friendly ping on this, would there be any objections to splitting the > > memory.stat metrics out to be per hugepage size? > > I don't think it has to be either/or. We can add the total here, and a > per-size breakdown in a separate patch (with its own changelog)? > > That said, a per-size breakdown might make more sense in the hugetlb > cgroup controller. You're mentioning separate global resources, which > suggests this is about more explicitly controlled hugetlb use. > > From a memcg POV, all hugetlb is the same. It's just (non-swappable) > memory consumed by the cgroup. > Ok, that's fair. We have a local patch that tracks hugetlb usage, admittedly for all hugetlb sizes, in struct mem_cgroup_per_node so that we can provide a breakdown in memory.numa_stat because we can't get the per-node breakdown from hugetlb_cgroup. If there is interest in that breakdown, we could easily propose the patch.
