Commit f5164797 authored by Donet Tom's avatar Donet Tom Committed by Madhavan Srinivasan
Browse files

book3s64/radix : Optimize vmemmap start alignment 



If we always align the vmemmap start to PAGE_SIZE, there is a
chance that we may end up allocating page-sized vmemmap backing
pages in RAM in the altmap not present case, because a PAGE_SIZE
aligned address is not PMD_SIZE-aligned.

In this patch, we are aligning the vmemmap start address to
PMD_SIZE if altmap is not present. This ensures that a PMD_SIZE
page is always allocated for the vmemmap mapping if altmap is
not present.

If altmap is present, Make sure we align the start vmemmap addr to
PAGE_SIZE so that we calculate the correct start_pfn in altmap
boundary check to decide whether we should use altmap or RAM based
backing memory allocation. Also the address need to be aligned for
set_pte operation. If the start addr is already PMD_SIZE aligned
and with in the altmap boundary then we will try to use a pmd size
altmap mapping else we go for page size  mapping.

So if altmap is present, we try to use the maximum number of
altmap pages; otherwise, we allocate a PMD_SIZE RAM page.

Signed-off-by: default avatarDonet Tom <donettom@linux.ibm.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/895c4afd912c85d344a2065e348fac90529ed48f.1750593372.git.donettom@linux.ibm.com
parent 58450938

arch/powerpc/mm/book3s64/radix_pgtable.c

+18 −11
Original line number Diff line number Diff line
@@ -1122,18 +1122,25 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in 
	pte_t *pte;



	/*

	 * Make sure we align the start vmemmap addr so that we calculate

	 * the correct start_pfn in altmap boundary check to decided whether

	 * we should use altmap or RAM based backing memory allocation. Also

	 * the address need to be aligned for set_pte operation.



	 * If the start addr is already PMD_SIZE aligned we will try to use

	 * a pmd mapping. We don't want to be too aggressive here beacause

	 * that will cause more allocations in RAM. So only if the namespace

	 * vmemmap start addr is PMD_SIZE aligned we will use PMD mapping.

	 * If altmap is present, Make sure we align the start vmemmap addr

	 * to PAGE_SIZE so that we calculate the correct start_pfn in

	 * altmap boundary check to decide whether we should use altmap or

	 * RAM based backing memory allocation. Also the address need to be

	 * aligned for set_pte operation. If the start addr is already

	 * PMD_SIZE aligned and with in the altmap boundary then we will

	 * try to use a pmd size altmap mapping else we go for page size

	 * mapping.

	 *

	 * If altmap is not present, align the vmemmap addr to PMD_SIZE and

	 * always allocate a PMD size page for vmemmap backing.

	 *

	 */



	if (altmap)

		start = ALIGN_DOWN(start, PAGE_SIZE);

	else

		start = ALIGN_DOWN(start, PMD_SIZE);



	for (addr = start; addr < end; addr = next) {

		next = pmd_addr_end(addr, end);
@@ -1159,7 +1166,7 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in 
			 * in altmap block allocation failures, in which case

			 * we fallback to RAM for vmemmap allocation.

			 */

			if (!IS_ALIGNED(addr, PMD_SIZE) || (altmap &&

			if (altmap && (!IS_ALIGNED(addr, PMD_SIZE) ||

			    altmap_cross_boundary(altmap, addr, PMD_SIZE))) {

				/*

				 * make sure we don't create altmap mappings