On Wed, Dec 05, 2018 at 10:40:45AM +0200, Mike Rapoport wrote: >On Wed, Dec 05, 2018 at 10:34:26AM +0800, Wei Yang wrote: >> Currently locking for memory hotplug is a little complicated. >> >> Generally speaking, we leverage the two global lock: >> >> * device_hotplug_lock >> * mem_hotplug_lock >> >> to serialise the process. >> >> While for the long term, we are willing to have more fine-grained lock >> to provide higher scalability. >> >> This patch divides Locking Internal section based on these two global >> locks to help readers to understand it. Also it adds some new finding to >> enrich it. >> >> [David: words arrangement] >> >> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx> >> --- >> Documentation/core-api/memory-hotplug.rst | 27 ++++++++++++++++++++++++--- >> 1 file changed, 24 insertions(+), 3 deletions(-) >> >> diff --git a/Documentation/core-api/memory-hotplug.rst b/Documentation/core-api/memory-hotplug.rst >> index de7467e48067..95662b283328 100644 >> --- a/Documentation/core-api/memory-hotplug.rst >> +++ b/Documentation/core-api/memory-hotplug.rst >> @@ -89,6 +89,20 @@ NOTIFY_STOP stops further processing of the notification queue. >> Locking Internals >> ================= >> >> +There are three locks involved in memory-hotplug, two global lock and one local > >typo: ^locks > Thanks :-) >> +lock: >> + >> +- device_hotplug_lock >> +- mem_hotplug_lock >> +- device_lock >> + >> +Currently, they are twisted together for all kinds of reasons. The following >> +part is divided into device_hotplug_lock and mem_hotplug_lock parts >> +respectively to describe those tricky situations. >> + >> +device_hotplug_lock >> +--------------------- >> + >> When adding/removing memory that uses memory block devices (i.e. ordinary RAM), >> the device_hotplug_lock should be held to: >> >> @@ -111,13 +125,20 @@ As the device is visible to user space before taking the device_lock(), this >> can result in a lock inversion. >> >> onlining/offlining of memory should be done via device_online()/ >> -device_offline() - to make sure it is properly synchronized to actions >> -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) >> +device_offline() - to make sure it is properly synchronized to actions via >> +sysfs. Even mem_hotplug_lock is used to protect the process, because of the > >I think it should be "Even if mem_hotplug_lock ..." > Ah, my poor English, will fix it in next version. :-) >> +lock inversion described above, holding device_hotplug_lock is still advised >> +(to e.g. protect online_type) >> + >> +mem_hotplug_lock >> +--------------------- >> >> When adding/removing/onlining/offlining memory or adding/removing >> heterogeneous/device memory, we should always hold the mem_hotplug_lock in >> write mode to serialise memory hotplug (e.g. access to global/zone >> -variables). >> +variables). Currently, we take advantage of this to serialise sparsemem's >> +mem_section handling in sparse_add_one_section() and >> +sparse_remove_one_section(). >> >> In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read >> mode allows for a quite efficient get_online_mems/put_online_mems >> -- >> 2.15.1 >> > >-- >Sincerely yours, >Mike. -- Wei Yang Help you, Help me
