xen: limit extra memory to a certain ratio of base (698bb8d1) · Commits · 戴 / test

arch/x86/xen/setup.c

+32 −0

Original line number	Diff line number	Diff line
		@@ -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";

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