diff options
| -rw-r--r-- | arch/x86/xen/setup.c | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c index 1e85e26efa69..6c9039e92f81 100644 --- a/arch/x86/xen/setup.c +++ b/arch/x86/xen/setup.c @@ -37,6 +37,18 @@ extern void xen_syscall32_target(void); /* Amount of extra memory space we add to the e820 ranges */ phys_addr_t xen_extra_mem_start, xen_extra_mem_size; +/* + * The maximum amount of extra memory compared to the base size. The + * main scaling factor is the size of struct page. At extreme ratios + * of base:extra, all the base memory can be filled with page + * structures for the extra memory, leaving no space for anything + * else. + * + * 10x seems like a reasonable balance between scaling flexibility and + * leaving a practically usable system. + */ +#define EXTRA_MEM_RATIO (10) + static __init void xen_add_extra_mem(unsigned long pages) { u64 size = (u64)pages * PAGE_SIZE; @@ -134,6 +146,7 @@ char * __init xen_memory_setup(void) int rc; struct xen_memory_map memmap; unsigned long extra_pages = 0; + unsigned long extra_limit; int i; max_pfn = min(MAX_DOMAIN_PAGES, max_pfn); @@ -196,6 +209,25 @@ char * __init xen_memory_setup(void) extra_pages += xen_return_unused_memory(xen_start_info->nr_pages, &e820); + /* + * Clamp the amount of extra memory to a EXTRA_MEM_RATIO + * factor the base size. On non-highmem systems, the base + * size is the full initial memory allocation; on highmem it + * is limited to the max size of lowmem, so that it doesn't + * get completely filled. + * + * In principle there could be a problem in lowmem systems if + * the initial memory is also very large with respect to + * lowmem, but we won't try to deal with that here. + */ + extra_limit = min(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)), + max_pfn + extra_pages); + + if (extra_limit >= max_pfn) + extra_pages = extra_limit - max_pfn; + else + extra_pages = 0; + xen_add_extra_mem(extra_pages); return "Xen"; |