On Tue, Sep 11, 2018 at 9:50 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > On Mon, Sep 10, 2018 at 4:43 PM, Alexander Duyck > <alexander.duyck@xxxxxxxxx> 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. > > In anticipation of potentially more DEBUG_VM options wanting runtime > control I'd propose creating a new "vm_debug=" option for this modeled > after "slub_debug=" along with a CONFIG_DEBUG_VM_ON to turn on all > options. > > That way there is more differentiation for debug cases like this that > have significant performance impact when enabled. > > CONFIG_DEBUG_VM leaves optional debug capabilities disabled by default > unless CONFIG_DEBUG_VM_ON is also set. Based on earlier discussions I would assume that CONFIG_DEBUG_VM would imply CONFIG_DEBUG_VM_ON anyway since we don't want most of these disabled by default. In my mind we should be looking at a selective "vm_debug_disable=" instead of something that would be turning on features. - Alex
