Ian Campbell 1431559200 x86, mm: Allow highmem user page tables to be disabled at boot time ... Distros generally (I looked at Debian, RHEL5 and SLES11) seem to enable CONFIG_HIGHPTE for any x86 configuration which has highmem enabled. This means that the overhead applies even to machines which have a fairly modest amount of high memory and which therefore do not really benefit from allocating PTEs in high memory but still pay the price of the additional mapping operations. Running kernbench on a 4G box I found that with CONFIG_HIGHPTE=y but no actual highptes being allocated there was a reduction in system time used from 59.737s to 55.9s. With CONFIG_HIGHPTE=y and highmem PTEs being allocated: Average Optimal load -j 4 Run (std deviation): Elapsed Time 175.396 (0.238914) User Time 515.983 (5.85019) System Time 59.737 (1.26727) Percent CPU 263.8 (71.6796) Context Switches 39989.7 (4672.64) Sleeps 42617.7 (246.307) With CONFIG_HIGHPTE=y but with no highmem PTEs being allocated: Average Optimal load -j 4 Run (std deviation): Elapsed Time 174.278 (0.831968) User Time 515.659 (6.07012) System Time 55.9 (1.07799) Percent CPU 263.8 (71.266) Context Switches 39929.6 (4485.13) Sleeps 42583.7 (373.039) This patch allows the user to control the allocation of PTEs in highmem from the command line ("userpte=nohigh") but retains the status-quo as the default. It is possible that some simple heuristic could be developed which allows auto-tuning of this option however I don't have a sufficiently large machine available to me to perform any particularly meaningful experiments. We could probably handwave up an argument for a threshold at 16G of total RAM. Assuming 768M of lowmem we have 196608 potential lowmem PTE pages. Each page can map 2M of RAM in a PAE-enabled configuration, meaning a maximum of 384G of RAM could potentially be mapped using lowmem PTEs. Even allowing generous factor of 10 to account for other required lowmem allocations, generous slop to account for page sharing (which reduces the total amount of RAM mappable by a given number of PT pages) and other innacuracies in the estimations it would seem that even a 32G machine would not have a particularly pressing need for highmem PTEs. I think 32G could be considered to be at the upper bound of what might be sensible on a 32 bit machine (although I think in practice 64G is still supported). It's seems questionable if HIGHPTE is even a win for any amount of RAM you would sensibly run a 32 bit kernel on rather than going 64 bit. Signed-off-by: Ian Campbell <ian.campbell@citrix.com> LKML-Reference: <1266403090-20162-1-git-send-email-ian.campbell@citrix.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>		2010-02-25 10:28:19 +01:00
..
ABI	ima: rename PATH_CHECK to FILE_CHECK	2010-02-07 03:06:23 -05:00
accounting	Documentation/: fix warnings from -Wmissing-prototypes in HOSTCFLAGS	2009-09-23 07:39:28 -07:00
acpi	ACPI: support customizing ACPI control methods at runtime	2009-12-11 01:50:08 -05:00
aoe
arm	OMAP: DSS2: Documentation for DSS2	2009-12-09 12:04:34 +02:00
auxdisplay	includecheck fix: Documentation, cfag12864b-example.c	2009-09-24 07:20:57 -07:00
blackfin	Blackfin: add an example showing how to use the gptimers API	2009-12-15 00:15:04 -05:00
block	Documentation: Rename Documentation/DMA-mapping.txt	2010-01-02 10:09:44 -08:00
blockdev	The DRBD driver	2009-10-01 21:17:49 +02:00
cdrom	debugfs: Fix terminology inconsistency of dir name to mount debugfs filesystem.	2009-06-15 21:30:28 -07:00
cgroups	blkio: Documentation	2009-12-03 19:28:53 +01:00
connector	connector: Provide the sender's credentials to the callback	2009-10-02 10:54:01 -07:00
console
cpu-freq	[CPUFREQ] fix default value for ondemand governor	2010-01-13 10:55:15 -05:00
cpuidle
cris
crypto	async_tx: add support for asynchronous RAID6 recovery operations	2009-08-29 19:09:27 -07:00
development-process	docs: Encourage better changelogs in the development process document	2009-06-04 10:32:49 -06:00
device-mapper	dm snapshot: add merge target	2009-12-10 23:52:30 +00:00
DocBook	DocBook: fix ioremap return type	2010-01-02 10:09:44 -08:00
driver-model	Driver core: driver_attribute parameters can often be const*	2009-12-23 11:23:43 -08:00
dvb	tree-wide: fix assorted typos all over the place	2009-12-04 15:39:55 +01:00
early-userspace
fault-injection	fault injection: correct function names in documentation	2010-02-02 18:11:22 -08:00
fb	viafb: documentation update	2009-12-16 07:20:05 -08:00
filesystems	proc: partially revert "procfs: provide stack information for threads"	2010-01-11 09:34:06 -08:00
firmware_class	driver core: fix documentation of request_firmware_nowait	2009-06-15 21:30:24 -07:00
frv
hwmon	Merge branch 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging	2010-01-11 09:45:55 -08:00
i2c	i2c: Get rid of struct i2c_client_address_data	2009-12-14 21:17:25 +01:00
i2o
ia64	Documentation/: fix warnings from -Wmissing-prototypes in HOSTCFLAGS	2009-09-23 07:39:28 -07:00
ide	ide: preserve Host Protected Area by default (v2)	2009-06-07 13:52:52 +02:00
infiniband	IB: Fix typo in ipoib.txt	2009-12-09 14:21:36 -08:00
input	Input: update multi-touch protocol documentation	2010-01-28 22:32:52 -08:00
ioctl	docs: large update to ioctl-number.txt	2010-01-11 09:34:04 -08:00
isdn	gigaset: documentation amendments	2009-12-08 20:30:41 -08:00
ja_JP	block: rename CONFIG_LBD to CONFIG_LBDAF	2009-06-19 08:08:50 +02:00
kbuild	kbuild: generate modules.builtin	2009-12-12 13:08:16 +01:00
kdump	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
ko_KR
kvm	KVM: x86: Extend KVM_SET_VCPU_EVENTS with selective updates	2009-12-27 13:36:33 -02:00
laptops	thinkpad-acpi: update volume subdriver documentation	2009-12-26 22:37:58 -05:00
lguest	tree-wide: fix assorted typos all over the place	2009-12-04 15:39:55 +01:00
m68k
make
mips
misc-devices	ad525x_dpot: new driver for AD525x digital potentiometers	2009-12-15 08:53:25 -08:00
mn10300	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
mtd	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
namespaces
netlabel
networking	Documentation/3c509: document ethtool support	2010-01-11 15:53:45 -08:00
parisc
PCI	Documentation: Rename Documentation/DMA-mapping.txt	2010-01-02 10:09:44 -08:00
pcmcia	pcmcia: remove now-defunct cs_error, pcmcia_error_{func,ret}	2009-11-09 08:30:06 +01:00
power	PM: Runtime PM documentation update	2009-12-22 20:43:40 +01:00
powerpc	Merge commit 'kumar/next' into merge	2009-12-21 09:30:42 +11:00
pps	LinuxPPS: core support	2009-06-18 13:04:04 -07:00
prctl
RCU	rcu: Add synchronize_srcu_expedited() to the documentation	2009-10-26 09:40:31 +01:00
s390	[S390] s390dbf: Add description for usage of "%s" in sprintf events	2009-09-11 10:29:53 +02:00
scheduler	sched: Documentation/sched-rt-group: Fix style issues & bump version	2009-06-21 13:12:46 +02:00
scsi	Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial	2009-12-09 19:43:33 -08:00
serial	tty: docs: serial/tty, add to ldisc methods	2009-12-11 15:18:05 -08:00
sh
sound	ALSA: Fix a typo in Procfile.txt	2009-12-26 18:37:44 +01:00
sparc
spi	tree-wide: fix assorted typos all over the place	2009-12-04 15:39:55 +01:00
sysctl	doc: Add documentation for bootloader_{type,version}	2009-12-11 14:28:56 -08:00
telephony
thermal	thermal: add sanity check for the passive attribute	2009-11-05 18:18:10 -05:00
timers	fix URL in hpet.txt	2009-11-09 09:40:54 +01:00
trace	tracing/documentation: Cover new frame pointer semantics	2010-01-26 17:00:39 -05:00
uml
usb	USB: power management documentation update	2009-12-23 11:34:09 -08:00
video4linux	V4L/DVB (13651): sh_mobile_ceu_camera: document the scaling and cropping algorithm	2009-12-16 09:27:20 -02:00
vm	HWPOISON: Use correct name for MADV_HWPOISON in documentation	2009-12-16 12:20:00 +01:00
w1	ds2482: Discard obsolete detect method	2009-10-04 22:53:41 +02:00
watchdog	Documentation/: fix warnings from -Wmissing-prototypes in HOSTCFLAGS	2009-09-23 07:39:28 -07:00
wimax
x86	USB: ehci-dbgp,documentation: Documentation updates for ehci-dbgp	2009-09-23 06:46:39 -07:00
zh_CN
00-INDEX	Bluetooth: Add documentation for Marvell Bluetooth driver	2009-08-22 14:25:32 -07:00
applying-patches.txt
atomic_ops.txt	Documentation/atomic_ops.txt: fix sample code	2009-06-16 19:47:52 -07:00
bad_memory.txt
basic_profiling.txt
binfmt_misc.txt
braille-console.txt	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
bt8xxgpio.txt
btmrvl.txt	Bluetooth: Add documentation for Marvell Bluetooth driver	2009-08-22 14:25:32 -07:00
BUG-HUNTING
cachetlb.txt
Changes	netfilter: xtables: document minimal required version	2009-12-14 14:52:10 +01:00
CodingStyle	trivial: fix typo milisecond/millisecond for documentation and source comments.	2009-06-12 18:01:46 +02:00
cpu-hotplug.txt	cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt	2009-12-17 11:43:29 +10:30
cpu-load.txt
cputopology.txt	Documentation: ABI: /sys/devices/system/cpu/cpu#/ topology files	2009-10-30 14:59:52 -07:00
credentials.txt
dcdbas.txt
debugging-modules.txt
debugging-via-ohci1394.txt	ieee1394: update URLs in debugging-via-ohci1394.txt	2009-10-03 09:28:11 +02:00
dell_rbu.txt	trivial: Documentation/dell_rbu.txt: fix typos	2009-06-12 18:01:50 +02:00
devices.txt
DMA-API.txt	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
DMA-attributes.txt
DMA-ISA-LPC.txt
dmaengine.txt
dontdiff	dontdiff: add generated	2009-12-12 13:08:13 +01:00
dynamic-debug-howto.txt
edac.txt	fix typos/grammos in Documentation/edac.txt	2009-12-04 15:39:53 +01:00
eisa.txt
email-clients.txt
feature-removal-schedule.txt	feature-removal-schedule: Add v4l1 drivers obsoleted by gspca sub drivers	2010-01-17 11:31:35 -02:00
flexible-arrays.txt	Update flex_arrays.txt	2009-10-15 07:25:20 -06:00
futex-requeue-pi.txt
gcov.txt	trivial: fix typo in CONFIG_DEBUG_FS in gcov doc	2009-09-21 15:14:56 +02:00
gpio.txt	gpiolib: add support for changing value polarity in sysfs	2009-12-16 07:20:01 -08:00
highuid.txt
HOWTO
hw_random.txt
initrd.txt
intel_txt.txt	x86, intel_txt: Intel TXT boot support	2009-07-21 11:49:06 -07:00
Intel-IOMMU.txt	intel-iommu: Kill DMAR_BROKEN_GFX_WA option.	2009-09-19 09:37:23 -07:00
io_ordering.txt
io-mapping.txt
IO-mapping.txt	Documentation: fix ioremap return type	2010-01-02 10:09:44 -08:00
iostats.txt
IPMI.txt
IRQ-affinity.txt
IRQ.txt
irqflags-tracing.txt
isapnp.txt
java.txt
kernel-doc-nano-HOWTO.txt	documentation: update kernel-doc-nano-HOWTO information	2010-01-11 09:34:07 -08:00
kernel-docs.txt
kernel-parameters.txt	x86, mm: Allow highmem user page tables to be disabled at boot time	2010-02-25 10:28:19 +01:00
keys-request-key.txt
keys.txt	KEYS: Add a keyctl to install a process's session keyring on its parent [try #6]	2009-09-02 21:29:22 +10:00
kmemcheck.txt	kmemcheck: update documentation	2009-07-01 22:36:22 +02:00
kmemleak.txt	kmemleak: add clear command support	2009-09-08 16:36:08 +01:00
kobject.txt	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
kprobes.txt	debugfs: Fix terminology inconsistency of dir name to mount debugfs filesystem.	2009-06-15 21:30:28 -07:00
kref.txt	kref: double kref_put() in my_data_handler()	2009-09-18 09:48:52 -07:00
ldm.txt
leds-class.txt	led: document sysfs interface	2009-08-28 15:21:12 -04:00
leds-lp3944.txt	leds: LED driver for National Semiconductor LP3944 Funlight Chip	2009-06-23 20:21:38 +01:00
local_ops.txt	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
lockdep-design.txt	lockdep: Fix typos in documentation	2009-08-07 12:03:46 +02:00
lockstat.txt	lockstat: Add usage info to Documentation/lockstat.txt	2009-12-06 13:20:02 +01:00
logo.gif
logo.txt
magic-number.txt
Makefile
ManagementStyle
mca.txt
md.txt	md: add 'recovery_start' per-device sysfs attribute	2009-12-14 12:58:57 +11:00
memory-barriers.txt
memory-hotplug.txt	mm: add numa node symlink for memory section in sysfs	2009-12-15 08:53:17 -08:00
memory.txt	Documentation/memory.txt: remove some very outdated recommendations	2009-09-22 07:17:26 -07:00
mono.txt
mutex-design.txt
nmi_watchdog.txt
nommu-mmap.txt	nommu: fix malloc performance by adding uninitialized flag	2009-12-15 08:53:24 -08:00
numastat.txt	mm: fix NUMA accounting in numastat.txt	2009-09-22 07:17:39 -07:00
oops-tracing.txt	docs: Describe the 'C' taint flag in oops-tracing.txt	2009-11-09 09:40:56 +01:00
parport-lowlevel.txt
parport.txt
pi-futex.txt
pnp.txt
preempt-locking.txt
printk-formats.txt
prio_tree.txt
rbtree.txt	trivial: rbtree.txt: fix rb_entry() parameters in sample code	2009-06-12 18:01:47 +02:00
rfkill.txt	rfkill: export persistent attribute in sysfs	2009-06-19 11:50:18 -04:00
robust-futex-ABI.txt	futex: documentation: fix inconsistent description of futex list_op_pending	2009-06-18 13:03:56 -07:00
robust-futexes.txt
rt-mutex-design.txt
rt-mutex.txt
rtc.txt	rtc: add boot_timesource sysfs attribute	2009-09-23 07:39:46 -07:00
SAK.txt
SecurityBugs
SELinux.txt
serial-console.txt
sgi-ioc4.txt
sgi-visws.txt
slow-work.txt	SLOW_WORK: Move slow_work's proc file to debugfs	2009-12-01 08:20:31 -08:00
SM501.txt	trivial: Miscellaneous documentation typo fixes	2009-06-12 18:01:47 +02:00
Smack.txt
sparse.txt
spinlocks.txt	Documentation: rw_lock lessons learned	2009-12-14 09:46:56 -08:00
stable_api_nonsense.txt
stable_kernel_rules.txt	Doc/stable rules: add new cherry-pick logic	2009-12-23 11:23:43 -08:00
SubmitChecklist	doc: SubmitChecklist, add ioctls, remove OSDL reference	2009-12-16 07:20:06 -08:00
SubmittingDrivers
SubmittingPatches	docs: update patch size in SubmittingPatches	2009-10-01 16:11:12 -07:00
svga.txt
sysfs-rules.txt
sysrq.txt	sysrq, kdump: make sysrq-c consistent	2009-07-29 19:10:36 -07:00
tomoyo.txt
unaligned-memory-access.txt
unicode.txt
unshare.txt
VGA-softcursor.txt
vgaarbiter.txt	vgaarbiter: fix a typo in the vgaarbiter Documentation	2009-12-16 11:28:58 -08:00
video-output.txt
volatile-considered-harmful.txt
voyager.txt
zorro.txt