Re: [libvirt PATCH v2 0/4] Share cgroup code that is duplicated between QEMU and LXC

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On Wed, Sep 12, 2018 at 03:18:26PM +0200, Michal Privoznik wrote:
On 09/12/2018 12:46 PM, Pavel Hrdina wrote:
On Wed, Sep 12, 2018 at 10:57:32AM +0200, Fabiano Fidêncio wrote:
virLXCCgroupSetupBlkioTune() and qemuSetupBlkioCgroup() and
virLXCCgroupSetupCpuTune() and qemuSetupCpuCgroup() are the most similar
functions between QEMU and LXC code.

Let's move their common code to virCgroup.

Mind that the first two patches are basically preparing the ground for
the changes introduced in the last two patches.

Hi, definitely good idea to remove code duplication!

We have similar issue with the virDomainSetBlkioParameters for QEMU and
LXC drivers.  The code to set cgroup values is the same.

Since the common object is domain how about introducing
virDomainSetupBlkioTune and virDomainSetupMemTune and move it into
domain_conf.c, that way we don't have to extract domain specific data
into src/util.

I'd rather remove stuff from doman_conf.c than add something there. It's
already the biggest file by far margin:

libvirt.git $ find . -type f -iname \*.c -exec du -h {} \; | sort -h
416K    ./src/qemu/qemu_domain.c
696K    ./src/qemu/qemu_driver.c
956K    ./src/conf/domain_conf.c

And moving code from domain_conf is something we do from time to time.
Just look at all those virnet* includes at the beginning of domain_conf.h.

Another reason for moving the code out is that blkio tune is not domain
specific. In the future, we might want to limit say iohelper and thus
move it into its specific cgroup.

I'm not that convinced about 2/4 to be honest. Memory specification is
pretty much domain centric.

Both seem to follow cgroups to a point, so they're process-centric, not
domain-centric. So if they're needed on lower (src/util) layers,
separating them makes sense.

(Not that domain_conf does not deserve to get both the parser and the
formatter to be split out at this line count)

But it follows my first point - moving code
out from domain_conf.c. And it de-duplicates the code.


Another benefit is that it will not cause me merge conflicts because I'm
rewriting cgroup code and adding support for cgroup v2.

Such downstream branches should not interfere with upstream libvirt
development. IOW: it's your opportunity as a maintainer to offer to
merge this patch on top of your changes if merging them now would cause
you too much trouble. ;)

Jano


I don't think that code movement should cause that big of a trouble.
You'll get some context conflicts but that's always the case with 30+
unmerged patches.

Michal

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