Merge branch 'akpm' (patch-bomb from Andrew Morton)

Split page table lock

=====================

Originally, mm->page_table_lock spinlock protected all page tables of the

mm_struct. But this approach leads to poor page fault scalability of

multi-threaded applications due high contention on the lock. To improve

scalability, split page table lock was introduced.

With split page table lock we have separate per-table lock to serialize

access to the table. At the moment we use split lock for PTE and PMD

tables. Access to higher level tables protected by mm->page_table_lock.

There are helpers to lock/unlock a table and other accessor functions:

 - pte_offset_map_lock()

	maps pte and takes PTE table lock, returns pointer to the taken

	lock;

 - pte_unmap_unlock()

	unlocks and unmaps PTE table;

 - pte_alloc_map_lock()

	allocates PTE table if needed and take the lock, returns pointer

	to taken lock or NULL if allocation failed;

 - pte_lockptr()

	returns pointer to PTE table lock;

 - pmd_lock()

	takes PMD table lock, returns pointer to taken lock;

 - pmd_lockptr()

	returns pointer to PMD table lock;

Split page table lock for PTE tables is enabled compile-time if

CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.

If split lock is disabled, all tables guaded by mm->page_table_lock.

Split page table lock for PMD tables is enabled, if it's enabled for PTE

tables and the architecture supports it (see below).

Hugetlb and split page table lock

---------------------------------

Hugetlb can support several page sizes. We use split lock only for PMD

level, but not for PUD.

Hugetlb-specific helpers:

 - huge_pte_lock()

	takes pmd split lock for PMD_SIZE page, mm->page_table_lock

	otherwise;

 - huge_pte_lockptr()

	returns pointer to table lock;

Support of split page table lock by an architecture

---------------------------------------------------

There's no need in special enabling of PTE split page table lock:

everything required is done by pgtable_page_ctor() and pgtable_page_dtor(),

which must be called on PTE table allocation / freeing.

Make sure the architecture doesn't use slab allocator for page table

allocation: slab uses page->slab_cache and page->first_page for its pages.

These fields share storage with page->ptl.

PMD split lock only makes sense if you have more than two page table

levels.

PMD split lock enabling requires pgtable_pmd_page_ctor() call on PMD table

allocation and pgtable_pmd_page_dtor() on freeing.

Allocation usually happens in pmd_alloc_one(), freeing in pmd_free(), but

make sure you cover all PMD table allocation / freeing paths: i.e X86_PAE

preallocate few PMDs on pgd_alloc().

With everything in place you can set CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK.

NOTE: pgtable_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must

be handled properly.

page->ptl

---------

page->ptl is used to access split page table lock, where 'page' is struct

page of page containing the table. It shares storage with page->private

(and few other fields in union).

To avoid increasing size of struct page and have best performance, we use a

trick:

 - if spinlock_t fits into long, we use page->ptr as spinlock, so we

   can avoid indirect access and save a cache line.

 - if size of spinlock_t is bigger then size of long, we use page->ptl as

   pointer to spinlock_t and allocate it dynamically. This allows to use

   split lock with enabled DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC, but costs

   one more cache line for indirect access;

The spinlock_t allocated in pgtable_page_ctor() for PTE table and in

pgtable_pmd_page_ctor() for PMD table.

Please, never access page->ptl directly -- use appropriate helper.

config HAVE_DMA_CONTIGUOUS

	bool

config USE_GENERIC_SMP_HELPERS

	bool

config GENERIC_SMP_IDLE_THREAD

       bool

config SMP

	bool "Symmetric multi-processing support"

	depends on ALPHA_SABLE || ALPHA_LYNX || ALPHA_RAWHIDE || ALPHA_DP264 || ALPHA_WILDFIRE || ALPHA_TITAN || ALPHA_GENERIC || ALPHA_SHARK || ALPHA_MARVEL

	select USE_GENERIC_SMP_HELPERS

	---help---

	  This enables support for systems with more than one CPU. If you have

	  a system with only one CPU, like most personal computers, say N. If

	if (!pte)

		return NULL;

	page = virt_to_page(pte);

	pgtable_page_ctor(page);

	if (!pgtable_page_ctor(page)) {

		__free_page(page);

		return NULL;

	}

	return page;

}

config SMP

	bool "Symmetric Multi-Processing (Incomplete)"

	default n

	select USE_GENERIC_SMP_HELPERS

	help

	  This enables support for systems with more than one CPU. If you have

	  a system with only one CPU, like most personal computers, say N. If