mm: dynamically allocate page->ptl if it cannot be embedded to struct page

If split page table lock is in use, we embed the lock into struct page
of table's page.  We have to disable split lock, if spinlock_t is too
big be to be embedded, like when DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC
enabled.

This patch add support for dynamic allocation of split page table lock
if we can't embed it to struct page.

page->ptl is unsigned long now and we use it as spinlock_t if
sizeof(spinlock_t) <= sizeof(long), otherwise it's pointer to spinlock_t.

The spinlock_t allocated in pgtable_page_ctor() for PTE table and in
pgtable_pmd_page_ctor() for PMD table.  All other helpers converted to
support dynamically allocated page->ptl.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 19 insertions, 2 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 7aa02def4666..de31af256207 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -218,8 +218,6 @@ config SPLIT_PTLOCK_CPUS
         int
         default "999999" if ARM && !CPU_CACHE_VIPT
         default "999999" if PARISC && !PA20
-        default "999999" if DEBUG_SPINLOCK || DEBUG_LOCK_ALLOC
-        default "999999" if !64BIT && GENERIC_LOCKBREAK
         default "4"
 
 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
diff --git a/mm/memory.c b/mm/memory.c
index d05c6b10e926..24ffae2a530e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4270,3 +4270,22 @@ void copy_user_huge_page(struct page *dst, struct page *src,
         }
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
+
+#if USE_SPLIT_PTE_PTLOCKS
+bool __ptlock_alloc(struct page *page)
+{
+        spinlock_t *ptl;
+
+        ptl = kmalloc(sizeof(spinlock_t), GFP_KERNEL);
+        if (!ptl)
+                return false;
+        page->ptl = (unsigned long)ptl;
+        return true;
+}
+
+void __ptlock_free(struct page *page)
+{
+        if (sizeof(spinlock_t) > sizeof(page->ptl))
+                kfree((spinlock_t *)page->ptl);
+}
+#endif