mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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c2452f3278
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> |
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atm | ||
auxdisplay | ||
base | ||
block | ||
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cdrom | ||
char | ||
clocksource | ||
connector | ||
cpufreq | ||
cpuidle | ||
crypto | ||
dca | ||
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edac | ||
eisa | ||
firewire | ||
firmware | ||
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gpu | ||
hid | ||
hwmon | ||
i2c | ||
ide | ||
idle | ||
ieee1394 | ||
infiniband | ||
input | ||
isdn | ||
leds | ||
lguest | ||
macintosh | ||
mca | ||
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memstick | ||
message | ||
mfd | ||
misc | ||
mmc | ||
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net | ||
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of | ||
oprofile | ||
parisc | ||
parport | ||
pci | ||
pcmcia | ||
pnp | ||
power | ||
ps3 | ||
rapidio | ||
regulator | ||
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sh | ||
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spi | ||
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tc | ||
telephony | ||
thermal | ||
uio | ||
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virtio | ||
w1 | ||
watchdog | ||
xen | ||
zorro | ||
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Makefile |