On Mon, Apr 03, 2023 at 05:39:15PM +0300, Kirill A. Shutemov wrote: > On Mon, Apr 03, 2023 at 03:39:53PM +0200, Vlastimil Babka wrote: > > On 3/30/23 13:49, Kirill A. Shutemov wrote: > > > For testing purposes, it is useful to fake unaccepted memory in the > > > system. It helps to understand unaccepted memory overhead to the page > > > allocator. > > > > Ack on being useful for testing, but the question is if we want to also > > merge this patch into mainline as it is? > > I don't insist on getting it upstream, but it can be handy to debug > related bugs in the future. > > > > The patch allows to treat memory above the specified physical memory > > > address as unaccepted. > > > > > > The change only fakes unaccepted memory for page allocator. Memblock is > > > not affected. > > > > > > It also assumes that arch-provided accept_memory() on already accepted > > > memory is a nop. > > > > I guess to be in mainline it would have to at least gracefully handle the > > case of accept_memory actually not being a nop, and running on a system with > > actual unaccepted memory (probably by ignoring the parameter in such case). > > Then also the parameter would have to be documented. > > As it is written now, accept_memory() is nop on system with real > unaccepted memory if the memory is already accepted. Arch-specific code > will check against own records to see if the memory needs accepting. If > not, just return. > > And the option will not interfere with unaccepted memory declared by EFI > memmap. It can extend it, but that's it. > > Looks safe to me. > > > Speaking of documented parameters, I found at least two that seem a more > > generic variant of this (but I didn't look closely if that makes sense): > > > > efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] > > Add arbitrary attribute to specific memory range by > > updating original EFI memory map. As of now, efi_fake_mem= can adjust attributes of memory. Unaccepted is type of memory, not an attribute. I guess we can allow it override type too. But syntax is going to be fun. > > memmap=<size>%<offset>-<oldtype>+<newtype> > > [KNL,ACPI] Convert memory within the specified region > > from <oldtype> to <newtype>. If "-<oldtype>" is left It overrides E820 map, but unaccepted memory is not represented there. Unaccepted memory is just RAM in E820. -- Kiryl Shutsemau / Kirill A. Shutemov
