linux/arch/i386
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
..
boot [PATCH] fbdev: Resurrect hooks to get EDID from firmware 2005-09-09 13:57:59 -07:00
crypto
kernel [PATCH] mm: i386 sh sh64 ready for split ptlock 2005-10-29 21:40:41 -07:00
lib [LIB]: Consolidate _atomic_dec_and_lock() 2005-09-14 21:47:01 -07:00
mach-default [PATCH] useless includes of linux/irq.h in arch/i386 2005-09-26 18:29:50 -07:00
mach-es7000
mach-generic
mach-visws [PATCH] useless includes of linux/irq.h in arch/i386 2005-09-26 18:29:50 -07:00
mach-voyager [PATCH] useless includes of linux/irq.h in arch/i386 2005-09-26 18:29:50 -07:00
math-emu
mm [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
oprofile [PATCH] mm: kill check_user_page_readable 2005-10-29 21:40:41 -07:00
pci [PATCH] PCI fixup for Toshiba laptops and ohci1394 2005-10-28 15:37:02 -07:00
power [PATCH] useless includes of linux/irq.h in arch/i386 2005-09-26 18:29:50 -07:00
defconfig
Kconfig [LIB]: Consolidate _atomic_dec_and_lock() 2005-09-14 21:47:01 -07:00
Kconfig.debug
Makefile