Re: [PATCH v3 0/6] Composefs: an opportunistically sharing verified image filesystem

[Amir Goldstein]

On Wed, Feb 1, 2023 at 6:28 AM Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
>
> Hi all,
>
> There are some updated performance statistics with different
> combinations on my test environment if you are interested.
>

Cool report!

>
> On 1/27/23 6:24 PM, Gao Xiang wrote:
> > ...
> >
> > I've made a version and did some test, it can be fetched from:
> > git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git -b
> > experimental
> >
>
> Setup
> ======
> CPU: x86_64 Intel(R) Xeon(R) Platinum 8269CY CPU @ 2.50GHz
> Disk: 6800 IOPS upper limit
> OS: Linux v6.2 (with composefs v3 patchset)
>
> I build erofs/squashfs images following the scripts attached on [1],
> with each file in the rootfs tagged with "metacopy" and "redirect" xattr.
>
> The source rootfs is from the docker image of tensorflow [2].
>
> The erofs images are built with mkfs.erofs with support for sparse file
> added [3].
>
> [1]
> https://lore.kernel.org/linux-fsdevel/5fb32a1297821040edd8c19ce796fc0540101653.camel@xxxxxxxxxx/
> [2]
> https://hub.docker.com/layers/tensorflow/tensorflow/2.10.0/images/sha256-7f9f23ce2473eb52d17fe1b465c79c3a3604047343e23acc036296f512071bc9?context=explore
> [3]
> https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/commit/?h=experimental&id=7c49e8b195ad90f6ca9dfccce9f6e3e39a8676f6
>
>
>
> Image size
> ===========
> 6.4M large.composefs
> 5.7M large.composefs.w/o.digest (w/o --compute-digest)
> 6.2M large.erofs
> 5.2M large.erofs.T0 (with -T0, i.e. w/o nanosecond timestamp)
> 1.7M large.squashfs
> 5.8M large.squashfs.uncompressed (with -noI -noD -noF -noX)
>
> (large.erofs.T0 is built without nanosecond timestamp, so that we get
> smaller disk inode size (same with squashfs).)
>
>
> Runtime Perf
> =============
>
> The "uncached" column is tested with:
> hyperfine -p "echo 3 > /proc/sys/vm/drop_caches" "ls -lR $MNTPOINT"
>
>
> While the "cached" column is tested with:
> hyperfine -w 1 "ls -lR $MNTPOINT"
>
>
> erofs and squashfs are mounted with loopback device.
>
>
>                                   | uncached(ms)| cached(ms)
> ----------------------------------|-------------|-----------
> composefs (with digest)           | 326         | 135
> erofs (w/o -T0)                   | 264         | 172
> erofs (w/o -T0) + overlayfs       | 651         | 238

This is a nice proof of the overlayfs "early lookup" overhead.
As I wrote, this overhead could be optimized by doing "lazy lookup"
on open like composefs does.

Here is a suggestion for a simple test variant that could be used to
approximate the expected improvement -
if you set all the metacopy files in erofs to redirect to the same
lower block, most of the lower lookup time will be amortized
because all but the first lower lookup are cached.
If you get a performance number with erofs + overlayfs that are
close to composefs performance numbers, it will prove the point
that same functionality and performance could be achieved by
modifying ovelrayfs/mkfs.erofs.

Thanks,
Amir.