On 20/08/2018 12:30, Peter Xu wrote:
>>> +
>>> + /*
>>> + * The default size is (slightly) not enough to put the page
>>> + * tables for the dirty logging memory region. Extend it
>>> + * depending on how big a region we're testing upon
>>> + */
>>> + mem_size = DEFAULT_GUEST_PHY_PAGES + TEST_MEM_PAGES / 512 * 2;
>> Hmm, now I see why you need the argument; I thought you were just adding
>> more memory for the test pages there but you are (correctly) using a
>> separate memory slot. If it's about the page tables, maybe you could
>> pass TEST_MEM_PAGES to vm_create_default and then do the computation in
>> vm_create_default? (Therefore scrapping my suggestion in patch 4/5).
> This computation totally comes from the requirement for bigger page
> tables (e.g., 4K page contains 512 page entries on 64bit x86 hosts),
Yes, exactly. So if you pass TEST_MEM_PAGES (number of pages that will
be virt_mapped outside vm_create_default) to vm_create_default, or 0 for
other tests, it can compute the amount of memory that you need for the
page tables. You can choose whether to use *2 for virt_mapping to 1G
pages, or *4 for virt_mapping 4KB pages. For example
mem_size = DEFAULT_GUEST_PHY_PAGES + extra_mapped_pages / 512 * 4;
> I'm just afraid that people might need to expand that for other
> reasons. One thing I can think of is when the ELF is too big to be
> put into the VM memory due to some reason, then the VM memory size
> will depend on something else rather than the size of page tables.
That can be covered by increasing DEFAULT_GUEST_PHY_PAGES, by loading
the ELF file before you compute the number, or ultimately by splitting
the test to a separate executable.
Paolo
