linux/arch/um
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
..
drivers [PATCH] uml: revert block driver use of host AIO 2005-10-12 08:22:26 -07:00
include [PATCH] mm: uml kill unused 2005-10-29 21:40:42 -07:00
kernel [PATCH] mm: split page table lock 2005-10-29 21:40:42 -07:00
os-Linux [PATCH] uml: revert block driver use of host AIO 2005-10-12 08:22:26 -07:00
scripts [PATCH] uml: allow building .s/.i/.lst files from userspace files 2005-10-10 08:36:00 -07:00
sys-i386 [PATCH] uml: Fix sysrq-r support for skas mode 2005-10-04 13:22:01 -07:00
sys-ia64 Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sys-ppc [PATCH] uml: stack dump fix 2005-05-28 16:46:13 -07:00
sys-x86_64 [PATCH] uml: fix x86_64 with !CONFIG_FRAME_POINTER 2005-10-10 08:37:59 -07:00
config.release Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
defconfig [PATCH] uml: skas0 - separate kernel address space on stock hosts 2005-07-07 18:23:44 -07:00
Kconfig [PATCH] uml: mark SMP on UML/x86_64 as broken 2005-09-05 00:06:22 -07:00
Kconfig.char [PATCH] uml: Rename Kconfig files to be like the other arches 2005-09-05 00:06:19 -07:00
Kconfig.debug [PATCH] uml: workaround GDB problems on debugging 2005-09-05 00:06:20 -07:00
Kconfig.i386 [PATCH] uml: UML/i386 cmpxchg fix 2005-09-17 11:50:01 -07:00
Kconfig.net [PATCH] uml: Rename Kconfig files to be like the other arches 2005-09-05 00:06:19 -07:00
Kconfig.scsi [PATCH] uml: Rename Kconfig files to be like the other arches 2005-09-05 00:06:19 -07:00
Kconfig.x86_64 [PATCH] uml: mark SMP on UML/x86_64 as broken 2005-09-05 00:06:22 -07:00
Makefile [PATCH] Uml: hide commands when not being verbose 2005-10-10 08:36:00 -07:00
Makefile-i386 [PATCH] uml makefiles sanitized 2005-09-29 08:46:26 -07:00
Makefile-ia64 Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile-os-Linux Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile-ppc Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile-skas [PATCH] uml makefiles sanitized 2005-09-29 08:46:26 -07:00
Makefile-tt Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Makefile-x86_64 [PATCH] uml makefiles sanitized 2005-09-29 08:46:26 -07:00