linux_dsm_epyc7002/drivers
Nick Piggin c2452f3278 shrink struct dentry
struct dentry is one of the most critical structures in the kernel. So it's
sad to see it going neglected.

With CONFIG_PROFILING turned on (which is probably the common case at least
for distros and kernel developers), sizeof(struct dcache) == 208 here
(64-bit). This gives 19 objects per slab.

I packed d_mounted into a hole, and took another 4 bytes off the inline
name length to take the padding out from the end of the structure. This
shinks it to 200 bytes. I could have gone the other way and increased the
length to 40, but I'm aiming for a magic number, read on...

I then got rid of the d_cookie pointer. This shrinks it to 192 bytes. Rant:
why was this ever a good idea? The cookie system should increase its hash
size or use a tree or something if lookups are a problem. Also the "fast
dcookie lookups" in oprofile should be moved into the dcookie code -- how
can oprofile possibly care about the dcookie_mutex? It gets dropped after
get_dcookie() returns so it can't be providing any sort of protection.

At 192 bytes, 21 objects fit into a 4K page, saving about 3MB on my system
with ~140 000 entries allocated. 192 is also a multiple of 64, so we get
nice cacheline alignment on 64 and 32 byte line systems -- any given dentry
will now require 3 cachelines to touch all fields wheras previously it
would require 4.

I know the inline name size was chosen quite carefully, however with the
reduction in cacheline footprint, it should actually be just about as fast
to do a name lookup for a 36 character name as it was before the patch (and
faster for other sizes). The memory footprint savings for names which are
<= 32 or > 36 bytes long should more than make up for the memory cost for
33-36 byte names.

Performance is a feature...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2008-12-31 18:07:38 -05:00
..
accessibility
acpi Merge branches 'tracing/ftrace', 'tracing/hw-branch-tracing' and 'tracing/ring-buffer'; commit 'v2.6.28' into tracing/core 2008-12-25 13:11:00 +01:00
amba
ata Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2008-12-30 17:43:10 -08:00
atm atm: Driver for Solos PCI ADSL2+ card. 2008-12-26 01:26:11 -08:00
auxdisplay
base
block Merge git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus 2008-12-30 17:37:25 -08:00
bluetooth
cdrom cdrom: reduce stack usage of mmc_ioctl_dvd_read_struct 2008-12-29 08:28:43 +01:00
char Merge git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus 2008-12-30 17:37:25 -08:00
clocksource clocksource, acpi_pm.c: put acpi_pm_read_slow() under CONFIG_PCI 2008-12-12 15:05:28 +01:00
connector
cpufreq
cpuidle
crypto crypto: talitos - Ack done interrupt in isr instead of tasklet 2008-12-25 11:02:33 +11:00
dca
dio
dma
edac Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulus/powerpc 2008-12-28 16:54:33 -08:00
eisa
firewire firewire: fw-ohci: fix IOMMU resource exhaustion 2008-12-10 12:45:34 +01:00
firmware DMI: add dmi_match 2008-12-29 07:39:34 -05:00
gpio
gpu drm/i915: fix modeset devname allocation + agp init return check. 2008-12-29 18:18:19 +10:00
hid
hwmon
i2c Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
ide Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
idle
ieee1394 ieee1394: add quirk fix for Freecom HDD 2008-12-14 01:13:13 +01:00
infiniband Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/roland/infiniband 2008-12-30 17:45:28 -08:00
input Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
isdn Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2008-12-28 12:49:40 -08:00
leds
lguest lguest: struct device - replace bus_id with dev_name() 2008-12-30 09:26:12 +10:30
macintosh Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulus/powerpc 2008-12-28 16:54:33 -08:00
mca
md bio: allow individual slabs in the bio_set 2008-12-29 08:29:23 +01:00
media Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-2.6 2008-12-30 17:41:32 -08:00
memstick
message [SCSI] fusion: use ARRAY_SIZE 2008-12-29 11:24:17 -06:00
mfd
misc Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2008-12-28 12:49:40 -08:00
mmc Merge branch 'rmk-devel-mxc-pu-v2' of git://pasiphae.extern.pengutronix.de/git/imx/linux-2.6 into devel 2008-12-17 20:05:39 +00:00
mtd [ARM] MX3: add NAND support 2008-12-16 14:58:02 +01:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2008-12-30 17:43:10 -08:00
nubus
of of/gpio: Implement of_gpio_count() 2008-12-21 14:21:14 +11:00
oprofile shrink struct dentry 2008-12-31 18:07:38 -05:00
parisc
parport
pci Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-12-30 16:20:19 -08:00
pcmcia Merge branch 'mxc-pu-imxfb' of git://pasiphae.extern.pengutronix.de/git/imx/linux-2.6 into devel 2008-12-17 20:04:45 +00:00
pnp
power
ps3
rapidio rapidio: struct device - replace bus_id with dev_name(), dev_set_name() 2008-12-16 15:53:41 +11:00
regulator
rtc Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
s390 Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2008-12-30 17:43:10 -08:00
sbus
scsi Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 2008-12-30 17:43:10 -08:00
serial Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
sh sh: maple: Do not pass SLAB_POISON to kmem_cache_create() 2008-12-16 16:40:32 +09:00
sn
spi Merge git://git.marvell.com/orion into devel 2008-12-13 09:12:51 +00:00
ssb
staging Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2008-12-28 12:49:40 -08:00
tc
telephony
thermal
uio
usb Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
uwb
video Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm 2008-12-30 17:36:49 -08:00
virtio virtio: add PCI device release() function 2008-12-30 09:26:10 +10:30
w1 w1: fix slave selection on big-endian systems 2008-12-23 15:58:21 -08:00
watchdog Merge branch 'for-rmk' of git://git.kernel.org/pub/scm/linux/kernel/git/ycmiao/pxa-linux-2.6 into devel 2008-12-29 18:08:11 +00:00
xen Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-12-30 16:20:19 -08:00
zorro
Kconfig
Makefile