linux-kernel - Re: [PATCH 07/32] mm: Bring back vmalloc

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Date:   Sun, 21 May 2023 14:33:34 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     Lorenzo Stoakes <lstoakes@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-bcachefs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec

On Mon, May 15, 2023 at 03:26:43AM -0400, Kent Overstreet wrote:
> On Mon, May 15, 2023 at 12:13:43AM -0700, Eric Biggers wrote:
> > Sure, given that this is an optimization problem with a very small scope
> > (decoding 6 fields from a bitstream), I was hoping for something easier and
> > faster to iterate on than setting up a full kernel + bcachefs test environment
> > and reverse engineering 500 lines of shell script.  But sure, I can look into
> > that when I have a chance.
> 
> If you were actually wanting to help, that repository is the tool I use
> for kernel development and testing - it's got documentation.
> 
> It builds a kernel, boots a VM and runs a test in about 15 seconds, no
> need for lifting that code out to userspace.
> 

FYI, I had a go with your test framework today, but I ran into too many problems
to really bother with it.  In case you want to improve it, these are the
problems I ran into (so far).  The command I was trying to run, after having run
'./root_image create' as root as the README says to do, was
'build-test-kernel run -I ~/src/ktest/tests/bcachefs/perf.ktest':

- Error due to ~/src/ktest/tests/bcachefs/bcachefs-tools not existing.  Worked
  around by cloning the bcachefs-tools repo to this location.  (Note, it's not a
  git submodule, so updating the git submodules didn't help.)

- Error due to "Root image not found".  Worked around by recursively chown'ing
  /var/lib/ktest from root to my user.  (Note, the README says to run
  'root_image create' as root, which results in root ownership.)

- Error due to "cannot set up guest memory 'pc.ram': Cannot allocate memory".
  Worked around by editing tests/bcachefs/perf.ktest to change config-mem from
  32G to 16G.  (I have 32G memory total on this computer.)

- Error due to "failed to open /dev/vfio/10: No such file or directory".
  Enabling CONFIG_VFIO and CONFIG_VFIO_PCI in my host kernel didn't help.  It
  seems the test is hardcoded to expect PCI passthrough to be set up with a
  specific device.  I'd have expected it to just set up a standard virtual disk.