Re: [PATCH 05/10] powerpc/hugetlb: Split the function 'huge_pte_alloc'

On 04/11/2016 07:21 PM, Balbir Singh wrote:

On 07/04/16 15:37, Anshuman Khandual wrote:

quoted

Currently the function 'huge_pte_alloc' has got two versions, one for the
BOOK3S server and the other one for the BOOK3E embedded platforms. This
change splits only the BOOK3S server version into two parts, one for the
ARCH_WANT_GENERAL_HUGETLB config implementation and the other one for
everything else. This change is one of the prerequisites towards enabling
ARCH_WANT_GENERAL_HUGETLB config option on POWER platform.

Signed-off-by: Anshuman Khandual <redacted>
---
 arch/powerpc/mm/hugetlbpage.c | 67 +++++++++++++++++++++++++++----------------
 1 file changed, 43 insertions(+), 24 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index d991b9e..e453918 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c

@@ -59,6 +59,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
 	return __find_linux_pte_or_hugepte(mm->pgd, addr, NULL, NULL);
 }
 
+#ifndef CONFIG_ARCH_WANT_GENERAL_HUGETLB
 static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 			   unsigned long address, unsigned pdshift, unsigned pshift)
 {

@@ -116,6 +117,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
+#endif /* !CONFIG_ARCH_WANT_GENERAL_HUGETLB */
 
 /*
  * These macros define how to determine which level of the page table holds

@@ -130,6 +132,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 #endif
 
 #ifdef CONFIG_PPC_BOOK3S_64
+#ifndef CONFIG_ARCH_WANT_GENERAL_HUGETLB
 /*
  * At this point we do the placement change only for BOOK3S 64. This would
  * possibly work on other subarchs.

@@ -145,32 +148,23 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz
 
 	addr &= ~(sz-1);
 	pg = pgd_offset(mm, addr);
-
-	if (pshift == PGDIR_SHIFT)
-		/* 16GB huge page */
-		return (pte_t *) pg;
-	else if (pshift > PUD_SHIFT)
-		/*
-		 * We need to use hugepd table
-		 */
+	if (pshift > PUD_SHIFT) {
 		hpdp = (hugepd_t *)pg;
-	else {
-		pdshift = PUD_SHIFT;
-		pu = pud_alloc(mm, pg, addr);
-		if (pshift == PUD_SHIFT)
-			return (pte_t *)pu;
-		else if (pshift > PMD_SHIFT)
-			hpdp = (hugepd_t *)pu;
-		else {
-			pdshift = PMD_SHIFT;
-			pm = pmd_alloc(mm, pu, addr);
-			if (pshift == PMD_SHIFT)
-				/* 16MB hugepage */
-				return (pte_t *)pm;
-			else
-				hpdp = (hugepd_t *)pm;
-		}
+		goto hugepd_search;
 	}
+
+	pdshift = PUD_SHIFT;
+	pu = pud_alloc(mm, pg, addr);
+	if (pshift > PMD_SHIFT) {
+		hpdp = (hugepd_t *)pu;
+		goto hugepd_search;
+	}
+
+	pdshift = PMD_SHIFT;
+	pm = pmd_alloc(mm, pu, addr);
+	hpdp = (hugepd_t *)pm;
+
+hugepd_search:
 	if (!hpdp)
 		return NULL;
 

@@ -182,6 +176,31 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz
 	return hugepte_offset(*hpdp, addr, pdshift);
 }
 
+#else /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
+pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz)

This is confusing, aren't we using the one from mm/hugetlb.c?

We are using huge_pte_alloc() from mm/hugetlb.c only when we have
CONFIG_ARCH_WANT_GENERAL_HUGETLB enabled. For every thing else we
use the definition here for BOOK3S platforms.

quoted

+{
+	pgd_t *pg;
+	pud_t *pu;
+	pmd_t *pm;
+	unsigned pshift = __ffs(sz);
+
+	addr &= ~(sz-1);

Am I reading this right? Shouldn't this be addr &= ~(1 << pshift - 1)

Both are same. __ffs() computes the __ilog2 of the size and arrives at
the page shift. Here we use the size directly instead.