Although initramfs-tools is available . kernel has no initramfs support

[ghost]

When having multiple USB devices attached to the Pi, and having root fs on one of them, it is required for reliable boot to have a cmdline.txt containing "root=LABEL=..." instead of "root=/dev/sdXY" since the device naming is not fixed. This requires an initramfs.

It would be nice to have initramfs support not only in userspace but in the kernel as well (I don't see any drawbacks).

I rebuilt the Pi's kernel (3.6.11) to have it support initramfs using the following in .config:

CONFIG_BLK_DEV_INITRD=y
CONFIG_INITRAMFS_SOURCE=""
CONFIG_RD_GZIP=y

Using this kernel I was able to have it mount "root=LABEL=..."

[popcornmix]

It would be nice to have initramfs support not only in userspace but in the kernel as well (I don't see any drawbacks).

What is the free memory reported after boot with and without the change?

[ghost]

I assume these are the numbers you need:

free output on standard kernel 3.6.11+:
total used free shared buffers cached
Mem: 448776 218400 230376 0 16056 93132
-/+ buffers/cache: 109212 339564
Swap: 102396 0 102396

free output on 3.6.11+ with initramfs support:
total used free shared buffers cached
Mem: 448748 218160 230588 0 15824 93020
-/+ buffers/cache: 109316 339432
Swap: 102396 0 102396

free output on 3.6.11+ with initramfs support AND after using an initramfs to boot:
total used free shared buffers cached
Mem: 448748 221548 227200 0 19164 92824
-/+ buffers/cache: 109560 339188
Swap: 102396 0 102396

The total amount of mem seems to differ by 32k, but the other numbers don't seem very helpful.

[popcornmix]

I think the free memory in the first case is:
230376+16056+93132 = 339564
and with initramfs compiled in
230588+15824+93020 = 339432

So I think you've lost 132K. That seems a bit high for a feature <1% of people will make use of.

[ghost]

I think you are misinterpreting the numbers. The "used" figure tells you the amount of memory that's used in total, not the amount of memory that is used exclusively by the kernel. Actually the "used" figure always grows after boot because of the amount of disk data that is cached. For example, look at the following numbers after I had my Pi copy huge amounts of data from one disk to another:

           total       used       free     shared    buffers     cached

Mem: 448748 437816 10932 0 54688 223984
-/+ buffers/cache: 159144 289604
Swap: 102396 0 102396

This is the 3.6.11+ kernel with initramfs support AND after using an initramfs to boot. Because of all the cached disk blocks the "used" number (437816) has gone up to close the total amount of memory. Also the "cached" number (223984) has increased dramatically.

I still think the "total" number is the relevant one, see: http://www.redhat.com/advice/tips/meminfo.html

Quote: "MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code)"

(MemTotal in /proc/meminfo is the "total" number as presented by "free")

So that would imply that initramfs costs 32k RAM of a total of 256MB (Old Pi) or 512MB (New Pi), or 0.0122% (Old Pi) or 0.0061% (New Pi) of the available memory.

Although the Pi runs fine from the included SD card, unfortunately the SD card is slow (specifically for writes). So for several use cases having the root filesystem on a USB stick/disk may help a lot.

[ghost]

Reopened the issue; did not intentionally close it.

[ghost]

Another bonus when booting a USB root: No more SD card corruption when overclocking!

[mkj]

I'd like to see initramfs for a remote network recovery console. By my measurements I see around a 56kB increase in memory use. The numbers from adding free memory fluctuate quite a lot between boots, even with identical sdcard images. I've done 30x boots of each kernel in https://github.com/Torlus/qemu-rpi , averaged below using https://github.com/rustyrussell/stats . Even just the without-gz variant would be useful if memory is a concern.

Looking at free memory:

no initrd:     413035+6215.47+16684.5 = 435934kB
initrd gz:     412963+6216+16699.6    = 435878kB -> -56 kB
initrd no gz:  413002+6216+16693.1    = 435911kB -> -24 kB

Or looking at the "used column":

no initrd:    35732.7kB
initrd gz:    35788.7kB -> +56kB
initrd no gz: 35766.3kB -> +33.6kB

Measured results. Output was printed in rc.local. I've got /proc/meminfo if there's something relevant there too.

Current head 3.6.11+ (30 May, 5d5301e598) 
No initrd:
             total       used       free     shared    buffers     cached
Mem:        448768 35452-35956(35732.7+/-98) 412812-413316(413035+/-98)          0 6208-6216(6215.47+/-2) 16628-16820(16684.5+/-42)
Initrd with gz:
             total       used       free     shared    buffers     cached
Mem:        448752 35588-35968(35788.7+/-98) 412784-413164(412963+/-98)          0       6216 16648-16820(16699.6+/-50)
Initrd without gz:
             total       used       free     shared    buffers     cached
Mem:        448768 35564-35860(35766.3+/-80) 412908-413204(413002+/-80)          0       6216 16648-16820(16693.1+/-46)

[popcornmix]

Closing issue since there has been no activity for more than 2 months. Reopen if needed.