On Wed, Sep 12, 2018 at 7:10 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Mon 10-09-18 16:43:41, Alexander Duyck wrote: > > From: Alexander Duyck <alexander.h.duyck@xxxxxxxxx> > > > > On systems with a large amount of memory it can take a significant amount > > of time to initialize all of the page structs with the PAGE_POISON_PATTERN > > value. I have seen it take over 2 minutes to initialize a system with > > over 12GB of RAM. > > > > In order to work around the issue I had to disable CONFIG_DEBUG_VM and then > > the boot time returned to something much more reasonable as the > > arch_add_memory call completed in milliseconds versus seconds. However in > > doing that I had to disable all of the other VM debugging on the system. > > > > In order to work around a kernel that might have CONFIG_DEBUG_VM enabled on > > a system that has a large amount of memory I have added a new kernel > > parameter named "page_init_poison" that can be set to "off" in order to > > disable it. > > I am still not convinced that this all is worth the additional code. It > is much better than a new config option for sure. If we really want this > though then I suggest that the parameter handler should note the > disabled state (when CONFIG_DEBUG_VM is on) to the kernel log. I would > also make it explicit who might want to do that in the parameter > description. Anything specific in terms of the kernel log message we are looking for? I'll probably just go with "Page struct poisoning disabled by kernel command line option 'page_init_poison'" or something along those lines. > > + page_init_poison= [KNL] Boot-time parameter changing the > > + state of poisoning of page structures during early > > + boot. Used to verify page metadata is not accessed > > + prior to initialization. Available with > > + CONFIG_DEBUG_VM=y. > > + off: turn off poisoning > > + on: turn on poisoning (default) > > + > > what about the following wording or something along those lines > > Boot-time parameter to control struct page poisoning which is a > debugging feature to catch unitialized struct page access. This option > is available only for CONFIG_DEBUG_VM=y and it affects boot time > (especially on large systems). If there are no poisoning bugs reported > on the particular system and workload it should be safe to disable it to > speed up the boot time. That works for me. I will update it for the next release. Thanks. - Alex
