On Thu, Jan 5, 2023 at 11:09 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > Alexander Potapenko wrote: > > (+ Dan Williams) > > (resending with patch context included) > > > > On Mon, Jul 11, 2022 at 6:27 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > > > > > On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > > > > > KMSAN adds extra metadata fields to struct page, so it does not fit into > > > > 64 bytes anymore. > > > > > > Does this somehow cause extra space being used in all kernel configs? > > > If not, it would be good to note this in the commit message. > > > > > I actually couldn't verify this on QEMU, because the driver never got loaded. > > Looks like this increases the amount of memory used by the nvdimm > > driver in all kernel configs that enable it (including those that > > don't use KMSAN), but I am not sure how much is that. > > > > Dan, do you know how bad increasing MAX_STRUCT_PAGE_SIZE can be? > > Apologies I missed this several months ago. The answer is that this > causes everyone creating PMEM namespaces on v6.1+ to lose double the > capacity of their namespace even when not using KMSAN which is too > wasteful to tolerate. So, I think "6e9f05dc66f9 libnvdimm/pfn_dev: > increase MAX_STRUCT_PAGE_SIZE" needs to be reverted and replaced with > something like: > > diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig > index 79d93126453d..5693869b720b 100644 > --- a/drivers/nvdimm/Kconfig > +++ b/drivers/nvdimm/Kconfig > @@ -63,6 +63,7 @@ config NVDIMM_PFN > bool "PFN: Map persistent (device) memory" > default LIBNVDIMM > depends on ZONE_DEVICE > + depends on !KMSAN > select ND_CLAIM > help > Map persistent memory, i.e. advertise it to the memory > Looks like we still don't have a resolution for this problem. I have the following options in mind: 1. Set MAX_STRUCT_PAGE_SIZE to 80 (i.e. increase it by 2*sizeof(struct page *) added by KMSAN) instead of 128. 2. Disable storing of struct pages on device for KMSAN builds. , but if those are infeasible, we can always go for: 3. Disable KMSAN for NVDIMM and reflect it in Documentation. I am happy to send the patch if we decide this is the best option.
