Installing RemixOS to an internal drive

Your old pal syslinux is there to greet you
Your old pal syslinux is there to greet you

After initially running RemixOS, the new Android build for PCs, I decided that I would rather play with booting it natively from my SSD instead of from a USB device. Performance should be better, it would free my USB thumb drive up for other duties, and it would make booting more convenient.

This turned out to be a relatively simple operation. What follows is my methodology for doing that. Please note that these instructions assume you are running Linux.

Continue reading “Installing RemixOS to an internal drive”

Trying out RemixOS

The RemixOS boot logo
The RemixOS boot logo

I’ve always been one for trying out new operating systems, so when I heard news about the latest desktop-conversion effort from Jide I wanted to give it a try.

RemixOS is a proprietary offering based on the work of android-x86, which aims to bring the stock Android experience to commodity PCs. RemixOS adds on interface and convenience changes to make the operating system more usable on PC hardware. This includes UI changes such as multi-windows and a classic ‘desktop’.

The Alpha for PC was released this morning, and can be downloaded here. There was also a leaked version that landed a couple days earlier. If you’ve seen reviews online, most of them came from this. What follows are my impressions of the experience. Continue reading “Trying out RemixOS”

The ‘Try’ repository and its evolution

As the primary maintainers of the back end of the Try repository (in addition to the rest of Mercurial infrastructure) we are responsible for its care and feeding, making sure it is available, and a safe place to put your code before integration into trees.

Recently (the past few years actually) we’ve been experiencing that Mercurial has problems scaling to it’s activity. Here are some statistics for example:

  • 24550 Mercurial heads (this is reset every few months)
  • Head count correlated with the degraded performance
  • 4.3 GB in size, 203509 files without a working copy

One of the methods we’re attempting is to modify try so that each push is not a head, but is instead a bundle that can be applied cleanly to any mozilla-central tree.

By default when issuing a ‘hg clone’ from and to a local disk, it will create a hardlinked clone:


$ hg clone --time --debug --noupdate mozilla-central/ mozilla-central2/
linked 164701 files
listing keys for "bookmarks"
time: real 3.030 secs (user 1.080+0.000 sys 1.470+0.000)

$ du --apparent-size -hsxc mozilla-central*
1.3G   mozilla-central
49M    mozilla-central2
1.3G   total

These lightweight clones are the perfect environment to apply try heads to, because they will all be based off existing revs on mozilla-central anyway. To do that we can apply a try head bundle on top:


$ cd mozilla-central2/
$ hg unbundle $HOME/fffe1fc3a4eea40b47b45480b5c683fea737b00f.bundle
adding changesets
adding manifests
adding file changes
added 14 changesets with 55 changes to 52 files (+1 heads)
(run 'hg heads .' to see heads, 'hg merge' to merge)
$ hg heads|grep fffe1fc
changeset:   213681:fffe1fc3a4ee

This is great. Imagine if instead of ‘mozilla-central2’ this were named fffe1*, and could be stored in portable bundle format, and used to create repositories whenever they were needed. There is one problem though:


$ du -hsx --apparent-size mozilla-central*
1.3G	mozilla-central
536M	mozilla-central2

Our lightweight 49MB copy has turned into 536MB. This would be fine for just a few repositories, but we have tens of thousands. That means we’ll need to keep them in bundle format and turn them into repositories on demand. Thankfully this operation only takes about three seconds.

I’ve written a little bash script to go through the backlog of 24,553 try heads and generate bundles for each of them. Here is the script and some stats for the bundles:


$ ls *bundle|wc -l
24553

$ du -hsx
39G    .

$ cat makebundles.sh
#!/bin/bash

/usr/bin/parallel --gnu --jobs 16 \
    "test ! -f {}.bundle && \
    /usr/bin/hg -R /repo/hg/mozilla/try bundle --rev {} {}.bundle ::: \
    $(/usr/bin/hg -R /repo/hg/mozilla/try heads --template "{node} ")

If this tooling works well I’d like to start using this as the future method of submitting requests to try. Additionally if developers wanted, I could create a Mercurial extension to automate the bundling process and create a bundle submission engine for try.

Mozilla’s “try” repository

At Mozilla we use Mercurial for Firefox development. We have several repositories/trees that are used depending on where the code should be. If a developer wishes to test the code they have been developing, they can submit it to a Mercurial repository called ‘try‘, since running our entire test suite is not feasible on developer machines.

We have quite a bit of infrastructure around this including Tinderbox Pushlog (TBPL) and  more. This post deals with the infrastructure and problem we face while trying to scale the ‘try’ repository.

A few statistics:

  • The try repository currently has 17943 heads. These heads are never removed.
  • The try repository is about 3.6 GB in size.
  • Due to Mercurial’s on-wire HTTP protocol, this number of heads causes HTTP cloning to fail
  • There are roughly 81000 HTTP requests to try per day
  • To fix problems (mentioned below), the try repository is deleted and re-cloned from mozilla-central every few months

There are a number of problems associated with such a repository. One particularly nasty one has been present through several years of Mercurial development, and has been tricky in that it is seemingly unreproducible. The scenario is something like:

  • User ‘hg push’es some changes to a new head onto try
  • The push process takes a long time (sometimes between 10 minutes and hours)
  • A developer could issue an interrupt signal (ctrl+C) which causes the client to gracefully hang up and exit (his typically has no effect on the server
  • Subsequent pushes will hang with something similar to ‘remote: waiting for lock on repository /repo/hg/mozilla/try/ held by ‘hgssh1.dmz.scl3.mozilla.com:23974’
  • When this happens a hg process is running on the server has the following characteristics:
    • A ‘hg serve’ process runs single-threaded using 100% CPU
    • strace-ing and ltrace-ing reveal that the process is not making any system calls or external library calls
    • perf reveals that the process is spending all of its time inside some ambiguous python function
    • pdb yields that the process is spending all of its time in a function that (along some point in the stack trace) is going through ancestor calculations
    • The process will eventually exit cleanly
  • As operators there is nothing we can do that to alleviate the situation once the repository gets in this state. We simply inform developers and monitor the situation.

There have been several ideas on ways to alleviate the problem:

  • Periodically reset ‘try’. This is considered bad because 1) it loses history, and 2) it is disruptive to developers, who might have to re-submit try jobs again
  • Reset try on the SSH servers, but keep old try repositories on the HTTP servers. This has the potential to create unforeseen problems of growing these repositories even further on the HTTP servers. If reset (staggered from SSH server resets) this will remove unforeseen problem potential, but still lose history.
  • Creating bundle files out of pushes to ‘try’, then hosting these in an accessible location (S3, http webroot, etc). I will detail this method in a future blog post.

As of now though, try will periodically need to be reset as a countermeasure to the hangs mentioned in this post. Getting a reproducible test case might allow us to track down a bug or inefficiency in Mercurial to fix this problem after all. If you’d like to help us with this, please ping fubar or me (bkero) on irc.mozilla.org.