On Wed, 17 Jan 2024 at 11:39, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > That's a good point. If the microbenchmark isn't likely to be even > remotely realistic, maybe we should just revert the revert until if/when > somebody shows a real world impact. > > Linus, any objections to that? We use SLAB_ACCOUNT for much more common allocations like queued signals, so I would tend to agree with Jeff that it's probably just some not very interesting microbenchmark that shows any file locking effects from SLAB_ALLOC, not any real use. That said, those benchmarks do matter. It's very easy to say "not relevant in the big picture" and then the end result is that everything is a bit of a pig. And the regression was absolutely *ENORMOUS*. We're not talking "a few percent". We're talking a 33% regression that caused the revert: https://lore.kernel.org/lkml/20210907150757.GE17617@xsang-OptiPlex-9020/ I wish our SLAB_ACCOUNT wasn't such a pig. Rather than account every single allocation, it would be much nicer to account at a bigger granularity, possibly by having per-thread counters first before falling back to the obj_cgroup_charge. Whatever. It's kind of stupid to have a benchmark that just allocates and deallocates a file lock in quick succession spend lots of time incrementing and decrementing cgroup charges for that repeated alloc/free. However, that problem with SLAB_ACCOUNT is not the fault of file locking, but more of a slab issue. End result: I think we should bring in Vlastimil and whoever else is doing SLAB_ACCOUNT things, and have them look at that side. And then just enable SLAB_ACCOUNT for file locks. But very much look at silly costs in SLAB_ACCOUNT first, at least for trivial "alloc/free" patterns.. Vlastimil? Who would be the best person to look at that SLAB_ACCOUNT thing? See commit 3754707bcc3e (Revert "memcg: enable accounting for file lock caches") for the history here. Linus
