linux/arch
Hugh Dickins 4c21e2f244 [PATCH] mm: split page table lock
Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with
a many-threaded application which concurrently initializes different parts of
a large anonymous area.

This patch corrects that, by using a separate spinlock per page table page, to
guard the page table entries in that page, instead of using the mm's single
page_table_lock.  (But even then, page_table_lock is still used to guard page
table allocation, and anon_vma allocation.)

In this implementation, the spinlock is tucked inside the struct page of the
page table page: with a BUILD_BUG_ON in case it overflows - which it would in
the case of 32-bit PA-RISC with spinlock debugging enabled.

Splitting the lock is not quite for free: another cacheline access.  Ideally,
I suppose we would use split ptlock only for multi-threaded processes on
multi-cpu machines; but deciding that dynamically would have its own costs.
So for now enable it by config, at some number of cpus - since the Kconfig
language doesn't support inequalities, let preprocessor compare that with
NR_CPUS.  But I don't think it's worth being user-configurable: for good
testing of both split and unsplit configs, split now at 4 cpus, and perhaps
change that to 8 later.

There is a benefit even for singly threaded processes: kswapd can be attacking
one part of the mm while another part is busy faulting.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-29 21:40:42 -07:00
..
alpha [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
arm [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
arm26 [PATCH] mm: arches skip ptlock 2005-10-29 21:40:40 -07:00
cris [PATCH] mm: cris v32 mmu_context_lock 2005-10-29 21:40:42 -07:00
frv [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
h8300 kbuild: h8300,m68knommu,sh,sh64 use generic asm-offsets.h support 2005-09-09 20:28:49 +02:00
i386 [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
ia64 [PATCH] mm: flush_tlb_range outside ptlock 2005-10-29 21:40:40 -07:00
m32r [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
m68k [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
m68knommu [PATCH] m68knommu: startup code for the Drangen Engine 68328 based board 2005-09-12 20:04:15 -07:00
mips [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
parisc [PATCH] mm: parisc pte atomicity 2005-10-29 21:40:42 -07:00
ppc [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
ppc64 [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
s390 [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
sh [PATCH] mm: i386 sh sh64 ready for split ptlock 2005-10-29 21:40:41 -07:00
sh64 [PATCH] mm: i386 sh sh64 ready for split ptlock 2005-10-29 21:40:41 -07:00
sparc [PATCH] mm: arches skip ptlock 2005-10-29 21:40:40 -07:00
sparc64 [PATCH] mm: arches skip ptlock 2005-10-29 21:40:40 -07:00
um [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
v850 [PATCH] V850: C99 initializers for hw_interrupt_type structures 2005-09-10 10:06:27 -07:00
x86_64 [PATCH] mm: init_mm without ptlock 2005-10-29 21:40:40 -07:00
xtensa [PATCH] gfp_t: dma-mapping (xtensa) 2005-10-28 08:16:49 -07:00