On 9/18/2024 12:48 PM, Linus Torvalds wrote: > On Tue, 17 Sept 2024 at 16:34, Boqun Feng <boqun.feng@xxxxxxxxx> wrote: >> >> This series introduces hazard pointers [1] to kernel space. A TL;DR >> description of hazard pointers is "a scalable refcounting mechanim >> with RCU-like API". More information can be found at [2]. > > Please give actual "this is useful for X, and here is an actual real > load with numbers showing why it matters". > One of the use case where we had seen improvement is - Nginx web server throughput scalability with AppArmor enabled. For this use case we see refcount scalability problem when kref operations are done for AppArmor label object in Nginx worker's context. More details about this are captured @ [1] [2]. When we switch from kref to hazard pointer in apparmor_file_open(), we see ~7% improvement in Nginx throughput for this use case. While we were working on this problem, this refcount scalability issue got resolved recently with conditional ref acquisition [3] (however, there are new developments in apparmor code which might bring back the refcount problem [4]). [1] https://lore.kernel.org/lkml/20240110111856.87370-7-Neeraj.Upadhyay@xxxxxxx/T/ [2] https://lore.kernel.org/lkml/20240916050811.473556-1-Neeraj.Upadhyay@xxxxxxx/ [3] https://lore.kernel.org/lkml/20240620131524.156312-1-mjguzik@xxxxxxxxx/ [4] https://lore.kernel.org/lkml/71c0ea18-8b8b-402b-b03c-029aeedc2747@xxxxxxxxxxxxx/ - Neeraj > We don't just merge random infrastructure without a use-case and an > argument for it. > > Linus
