Re: [RFC PATCH 0/5] module: Remove stop_machine from module unloading
Ping? :) (2014/08/25 19:55), Masami Hiramatsu wrote: > Hi, > > Here is a series of patches which remove stop_machine() from > module unloading. > > Currently, each module unloading calls stop_machine()s 2 times. > One is for safely removing module from lists and one is to > check the reference counter. However, both are not necessary > for those purposes (required by current implementation). > > First, we can use RCU for the list operation, we just need > a synchronize_rcu right before cleaning up. > Second, the reference counter can be checked atomically by > using atomic_t, instead of per-cpu module_ref. Of course, > for BIG SMP machines, atomic operation is not efficient. > However, they usually don't need to remove most of modules too. > > In this series, I just fixed to use RCU for the module(and > bugs) list for the first stop_machine. > And for the second one, I replaced module_ref with atomic_t > and introduced a "module lockup" module load option, which > makes a module un-removable (lock up the module in kernel). > The lockup modules can not be removed except forced, and the > kernel skips module refcounting on those modules. Thus we > can minimize the performance impact on the BIG SMP machines. > > BTW, of course this requires to update libkmod to support > new MODULE_INIT_LOCKUP_MODULE flag. I'm not sure where is > good to send the patches I have. Sould I better sending > kmod patches on LKML? > > Thank you, > > --- > > Masami Hiramatsu (5): > module: Wait for RCU synchronizing before releasing a module > module: Unlink module with RCU synchronizing instead of stop_machine > lib/bug: Use RCU list ops for module_bug_list > module: Lock up a module when loading with a LOCLUP flag > module: Remove stop_machine from module unloading > > > include/linux/module.h| 22 ++ > include/trace/events/module.h |2 - > include/uapi/linux/module.h |1 > kernel/module.c | 147 > + > lib/bug.c | 20 -- > 5 files changed, 85 insertions(+), 107 deletions(-) > > -- > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC PATCH 0/5] module: Remove stop_machine from module unloading
Ping? :) (2014/08/25 19:55), Masami Hiramatsu wrote: Hi, Here is a series of patches which remove stop_machine() from module unloading. Currently, each module unloading calls stop_machine()s 2 times. One is for safely removing module from lists and one is to check the reference counter. However, both are not necessary for those purposes (required by current implementation). First, we can use RCU for the list operation, we just need a synchronize_rcu right before cleaning up. Second, the reference counter can be checked atomically by using atomic_t, instead of per-cpu module_ref. Of course, for BIG SMP machines, atomic operation is not efficient. However, they usually don't need to remove most of modules too. In this series, I just fixed to use RCU for the module(and bugs) list for the first stop_machine. And for the second one, I replaced module_ref with atomic_t and introduced a module lockup module load option, which makes a module un-removable (lock up the module in kernel). The lockup modules can not be removed except forced, and the kernel skips module refcounting on those modules. Thus we can minimize the performance impact on the BIG SMP machines. BTW, of course this requires to update libkmod to support new MODULE_INIT_LOCKUP_MODULE flag. I'm not sure where is good to send the patches I have. Sould I better sending kmod patches on LKML? Thank you, --- Masami Hiramatsu (5): module: Wait for RCU synchronizing before releasing a module module: Unlink module with RCU synchronizing instead of stop_machine lib/bug: Use RCU list ops for module_bug_list module: Lock up a module when loading with a LOCLUP flag module: Remove stop_machine from module unloading include/linux/module.h| 22 ++ include/trace/events/module.h |2 - include/uapi/linux/module.h |1 kernel/module.c | 147 + lib/bug.c | 20 -- 5 files changed, 85 insertions(+), 107 deletions(-) -- -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
