turbo boost emerge --sync and cvs up on gentoo-x86

As I wrote before portage operations are seek-bound and better handled by small loop device.

I had some problems creating such btrfs loop device, due to nonworking nocow loop devices, but now I have the solution!

The recipe:

  1. [for btrfs host FS] Make sure you have at least >=sys-fs/e2fsprogs-1.42.6 which has chattr/lsattr with nocow support.
  2. [for btrfs host FS] Mark a directory with loop device as nocow:

    $ mkdir -p /subvolumes/nocow-images/
    $ chattr +C /subvolumes/nocow-images/
    $ sudo lsattr -ld /subvolumes/nocow-images/
    /subvolumes/nocow-images/    No_COW
  3. Build small btrfs loop device:

    dd if=/dev/zero of="$image" bs=1M count=1K
    mkfs.btrfs           \
     -d single -m single \
     -L "$label"         \
     -l 32k -n 32k       \
     "$image"
  4. [for btrfs host FS] Make sure created file is nocow:

    $ lsattr -l /subvolumes/nocow-images/gentoo-32k.img
    /subvolumes/nocow-images/gentoo-32k.img No_COW
    $ /usr/sbin/filefrag /subvolumes/nocow-images/gentoo-32k.img
    /subvolumes/nocow-images/gentoo-32k.img: 1 extent found
  5. And mount it:

    /subvolumes/nocow-images/gentoo-32k.img         /gentoo-32k     btrfs           loop,nodatasum,noatime,nodiratime    0       0
  6. Amend /etc/portage/make.conf like that:

    PORTDIR=/gentoo-32k/portage

    and so on.

  7. Have fun!

Some notes:

Some numbers:

$ time emerge --sync # 72 seconds
...
real    1m12.111s
user    0m1.706s
sys     0m1.819s

gentoo-x86 $ time cvs up # ~4 minutes
...
real    4m35.208s
user    0m3.656s
sys     0m14.226s
Posted on November 17, 2012
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