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Donenfeld" , Uladzislau Rezki Cc: "Paul E. McKenney" , Jakub Kicinski , Julia Lawall , linux-block@vger.kernel.org, kernel-janitors@vger.kernel.org, bridge@lists.linux.dev, linux-trace-kernel@vger.kernel.org, Mathieu Desnoyers , kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Naveen N. 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Donenfeld wrote: > On Fri, Jun 14, 2024 at 02:35:33PM +0200, Uladzislau Rezki wrote: >> + /* Should a destroy process be deferred? */ >> + if (s->flags & SLAB_DEFER_DESTROY) { >> + list_move_tail(&s->list, &slab_caches_defer_destroy); >> + schedule_delayed_work(&slab_caches_defer_destroy_work, HZ); >> + goto out_unlock; >> + } > > Wouldn't it be smoother to have the actual kmem_cache_free() function > check to see if it's been marked for destruction and the refcount is > zero, rather than polling every one second? I mentioned this approach > in: https://lore.kernel.org/all/Zmo9-YGraiCj5-MI@zx2c4.com/ - > > I wonder if the right fix to this would be adding a `should_destroy` > boolean to kmem_cache, which kmem_cache_destroy() sets to true. And > then right after it checks `if (number_of_allocations == 0) > actually_destroy()`, and likewise on each kmem_cache_free(), it > could check `if (should_destroy && number_of_allocations == 0) > actually_destroy()`. I would prefer not to affect the performance of kmem_cache_free() by doing such checks, if possible. Ideally we'd have a way to wait/poll for the kfree_rcu() "grace period" expiring even with the batching that's implemented there. Even if it's pesimistically long to avoid affecting kfree_rcu() performance. The goal here is just to print the warnings if there was a leak and the precise timing of them shouldn't matter. The owning module could be already unloaded at that point? I guess only a kunit test could want to be synchronous and then it could just ask for kmem_cache_free() to wait synchronously. > Jason