s390/vmemmap: avoid memset(PAGE_UNUSED) when adding consecutive sections

#define PAGE_UNUSED 0xFD

static void vmemmap_use_sub_pmd(unsigned long start, unsigned long end)

/*

 * The unused vmemmap range, which was not yet memset(PAGE_UNUSED) ranges

 * from unused_pmd_start to next PMD_SIZE boundary.

 */

static unsigned long unused_pmd_start;

static void vmemmap_flush_unused_pmd(void)

{

	if (!unused_pmd_start)

		return;

	memset(__va(unused_pmd_start), PAGE_UNUSED,

	       ALIGN(unused_pmd_start, PMD_SIZE) - unused_pmd_start);

	unused_pmd_start = 0;

}

static void __vmemmap_use_sub_pmd(unsigned long start, unsigned long end)

{

	/*

	 * As we expect to add in the same granularity as we remove, it's

	memset(__va(start), 0, sizeof(struct page));

}

static void vmemmap_use_sub_pmd(unsigned long start, unsigned long end)

{

	/*

	 * We only optimize if the new used range directly follows the

	 * previously unused range (esp., when populating consecutive sections).

	 */

	if (unused_pmd_start == start) {

		unused_pmd_start = end;

		if (likely(IS_ALIGNED(unused_pmd_start, PMD_SIZE)))

			unused_pmd_start = 0;

		return;

	}

	vmemmap_flush_unused_pmd();

	__vmemmap_use_sub_pmd(start, end);

}

static void vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)

{

	void *page = __va(ALIGN_DOWN(start, PMD_SIZE));

	vmemmap_flush_unused_pmd();

	/* Could be our memmap page is filled with PAGE_UNUSED already ... */

	vmemmap_use_sub_pmd(start, end);

	__vmemmap_use_sub_pmd(start, end);

	/* Mark the unused parts of the new memmap page PAGE_UNUSED. */

	if (!IS_ALIGNED(start, PMD_SIZE))

		memset(page, PAGE_UNUSED, start - __pa(page));

	/*

	 * We want to avoid memset(PAGE_UNUSED) when populating the vmemmap of

	 * consecutive sections. Remember for the last added PMD the last

	 * unused range in the populated PMD.

	 */

	if (!IS_ALIGNED(end, PMD_SIZE))

		memset(__va(end), PAGE_UNUSED, __pa(page) + PMD_SIZE - end);

		unused_pmd_start = end;

}

/* Returns true if the PMD is completely unused and can be freed. */

{

	void *page = __va(ALIGN_DOWN(start, PMD_SIZE));

	vmemmap_flush_unused_pmd();

	memset(__va(start), PAGE_UNUSED, end - start);

	return !memchr_inv(page, PAGE_UNUSED, PMD_SIZE);

}