[RFC patch 1/7] thp: remove assumptions on pgtable_t type

Gerald Schaefer
2012-08-23T17:21:25Z

[-- Attachment #1: linux-3.5-thp-pgtable-prealloc.patch --]
[-- Type: text/plain, Size: 6340 bytes --]

The thp page table pre-allocation code currently assumes that pgtable_t
is of type "struct page *". This may not be true for all architectures,
so this patch removes that assumption by replacing the functions
prepare_pmd_huge_pte() and get_pmd_huge_pte() with two new functions
that can be defined architecture-specific.

It also removes two VM_BUG_ON checks for page_count() and page_mapcount()
operating on a pgtable_t. Apart from the VM_BUG_ON removal, there will
be no functional change introduced by this patch.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
---
include/asm-generic/pgtable.h | 6 +++++
include/linux/huge_mm.h | 1
mm/huge_memory.c | 46 +++++-------------------------------------
mm/pgtable-generic.c | 39 +++++++++++++++++++++++++++++++++++
4 files changed, 51 insertions(+), 41 deletions(-)

--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -443,6 +443,12 @@ static inline int pmd_write(pmd_t pmd)
return 0;
}
#endif /* __HAVE_ARCH_PMD_WRITE */
+#ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
+extern void pgtable_deposit(struct mm_struct *mm, pgtable_t pgtable);
+#endif
+#ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
+extern pgtable_t pgtable_withdraw(struct mm_struct *mm);
+#endif
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#ifndef pmd_read_atomic
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -11,7 +11,6 @@ extern int copy_huge_pmd(struct mm_struc
extern int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd,
pmd_t orig_pmd);
-extern pgtable_t get_pmd_huge_pte(struct mm_struct *mm);
extern struct page *follow_trans_huge_pmd(struct mm_struct *mm,
unsigned long addr,
pmd_t *pmd,
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -611,19 +611,6 @@ out:
}
__setup("transparent_hugepage=", setup_transparent_hugepage);

-static void prepare_pmd_huge_pte(pgtable_t pgtable,
- struct mm_struct *mm)
-{
- assert_spin_locked(&mm->page_table_lock);
-
- /* FIFO */
- if (!mm->pmd_huge_pte)
- INIT_LIST_HEAD(&pgtable->lru);
- else
- list_add(&pgtable->lru, &mm->pmd_huge_pte->lru);
- mm->pmd_huge_pte = pgtable;
-}
-
static inline pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
{
if (likely(vma->vm_flags & VM_WRITE))
@@ -665,7 +652,7 @@ static int __do_huge_pmd_anonymous_page(
*/
page_add_new_anon_rmap(page, vma, haddr);
set_pmd_at(mm, haddr, pmd, entry);
- prepare_pmd_huge_pte(pgtable, mm);
+ pgtable_deposit(mm, pgtable);
add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
mm->nr_ptes++;
spin_unlock(&mm->page_table_lock);
@@ -791,7 +778,7 @@ int copy_huge_pmd(struct mm_struct *dst_
pmdp_set_wrprotect(src_mm, addr, src_pmd);
pmd = pmd_mkold(pmd_wrprotect(pmd));
set_pmd_at(dst_mm, addr, dst_pmd, pmd);
- prepare_pmd_huge_pte(pgtable, dst_mm);
+ pgtable_deposit(dst_mm, pgtable);
dst_mm->nr_ptes++;

ret = 0;
@@ -802,25 +789,6 @@ out:
return ret;
}

-/* no "address" argument so destroys page coloring of some arch */
-pgtable_t get_pmd_huge_pte(struct mm_struct *mm)
-{
- pgtable_t pgtable;
-
- assert_spin_locked(&mm->page_table_lock);
-
- /* FIFO */
- pgtable = mm->pmd_huge_pte;
- if (list_empty(&pgtable->lru))
- mm->pmd_huge_pte = NULL;
- else {
- mm->pmd_huge_pte = list_entry(pgtable->lru.next,
- struct page, lru);
- list_del(&pgtable->lru);
- }
- return pgtable;
-}
-
static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long address,
@@ -876,7 +844,7 @@ static int do_huge_pmd_wp_page_fallback(
pmdp_clear_flush_notify(vma, haddr, pmd);
/* leave pmd empty until pte is filled */

- pgtable = get_pmd_huge_pte(mm);
+ pgtable = pgtable_withdraw(mm);
pmd_populate(mm, &_pmd, pgtable);

for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
@@ -1041,7 +1009,7 @@ int zap_huge_pmd(struct mmu_gather *tlb,
if (__pmd_trans_huge_lock(pmd, vma) == 1) {
struct page *page;
pgtable_t pgtable;
- pgtable = get_pmd_huge_pte(tlb->mm);
+ pgtable = pgtable_withdraw(tlb->mm);
page = pmd_page(*pmd);
pmd_clear(pmd);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
@@ -1358,7 +1326,7 @@ static int __split_huge_page_map(struct
pmd = page_check_address_pmd(page, mm, address,
PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
if (pmd) {
- pgtable = get_pmd_huge_pte(mm);
+ pgtable = pgtable_withdraw(mm);
pmd_populate(mm, &_pmd, pgtable);

for (i = 0, haddr = address; i < HPAGE_PMD_NR;
@@ -1971,8 +1939,6 @@ static void collapse_huge_page(struct mm
pte_unmap(pte);
__SetPageUptodate(new_page);
pgtable = pmd_pgtable(_pmd);
- VM_BUG_ON(page_count(pgtable) != 1);
- VM_BUG_ON(page_mapcount(pgtable) != 0);

_pmd = mk_pmd(new_page, vma->vm_page_prot);
_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
@@ -1990,7 +1956,7 @@ static void collapse_huge_page(struct mm
page_add_new_anon_rmap(new_page, vma, address);
set_pmd_at(mm, address, pmd, _pmd);
update_mmu_cache(vma, address, _pmd);
- prepare_pmd_huge_pte(pgtable, mm);
+ pgtable_deposit(mm, pgtable);
spin_unlock(&mm->page_table_lock);

#ifndef CONFIG_NUMA
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -120,3 +120,42 @@ void pmdp_splitting_flush(struct vm_area
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif
+
+#ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+void pgtable_deposit(struct mm_struct *mm, pgtable_t pgtable)
+{
+ assert_spin_locked(&mm->page_table_lock);
+
+ /* FIFO */
+ if (!mm->pmd_huge_pte)
+ INIT_LIST_HEAD(&pgtable->lru);
+ else
+ list_add(&pgtable->lru, &mm->pmd_huge_pte->lru);
+ mm->pmd_huge_pte = pgtable;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif
+
+#ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/* no "address" argument so destroys page coloring of some arch */
+pgtable_t pgtable_withdraw(struct mm_struct *mm)
+{
+ pgtable_t pgtable;
+
+ assert_spin_locked(&mm->page_table_lock);
+
+ /* FIFO */
+ pgtable = mm->pmd_huge_pte;
+ if (list_empty(&pgtable->lru))
+ mm->pmd_huge_pte = NULL;
+ else {
+ mm->pmd_huge_pte = list_entry(pgtable->lru.next,
+ struct page, lru);
+ list_del(&pgtable->lru);
+ }
+ return pgtable;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif