Re: [PATCH v3 0/4] PM: hibernate: LZ4 compression support

[Rafael J. Wysocki]

On Mon, Jan 22, 2024 at 2:16 PM Nikhil V <quic_nprakash@xxxxxxxxxxx> wrote:
>
> This patch series covers the following:
> 1. Renaming lzo* to generic names, except for lzo_xxx() APIs. This is
> used in the next patch where we move to crypto based APIs for
> compression. There are no functional changes introduced by this
> approach.
>
>
> 2. Replace LZO library calls with crypto generic APIs
>
> Currently for hibernation, LZO is the only compression algorithm
> available and uses the existing LZO library calls. However, there
> is no flexibility to switch to other algorithms which provides better
> results. The main idea is that different compression algorithms have
> different characteristics and hibernation may benefit when it uses
> alternate algorithms.
>
> By moving to crypto based APIs, it lays a foundation to use other
> compression algorithms for hibernation.
>
>
> 3. LZ4 compression
>
> Extend the support for LZ4 compression to be used with hibernation.
> The main idea is that different compression algorithms have different
> characteristics and hibernation may benefit when it uses any of these
> algorithms: a default algorithm, having higher compression rate but is
> slower(compression/decompression) and a secondary algorithm, that is
> faster(compression/decompression) but has lower compression rate.
>
> LZ4 algorithm has better decompression speeds over LZO. This reduces
> the hibernation image restore time.
> As per test results:
>                                     LZO             LZ4
> Size before Compression(bytes)   682696704       682393600
> Size after Compression(bytes)    146502402       155993547
> Decompression Rate               335.02 MB/s     501.05 MB/s
> Restore time                       4.4s             3.8s
>
> LZO is the default compression algorithm used for hibernation. Enable
> CONFIG_HIBERNATION_DEF_COMP_LZ4 to set the default compressor as LZ4.
>
> Compression Benchmarks: https://github.com/lz4/lz4
>
>
> 4. Support to select compression algorithm
>
> Currently the default compression algorithm is selected based on
> Kconfig. Introduce a kernel command line parameter "hib_compression" to
> override this behaviour.
>
> Users can set "hib_compression" command line parameter to specify
> the algorithm.
> Usage:
>     LZO: hib_compression=lzo
>     LZ4: hib_compression=lz4
> LZO is the default compression algorithm used with hibernation.
>
>
> Changes in v3:
>  - Rebased to v6.8-rc1 after resolving the minor conflicts.
>  - Link to v2:
>  https://lore.kernel.org/all/cover.1700048610.git.quic_nprakash@xxxxxxxxxxx/

I've applied the first 3 patches in the series (as 6.9 material), but
I'm not particularly happy with the last one.

First off, I'm not sure if a kernel command line parameter is the most
convenient way of selecting the compression algorithm.  Since (AFAICS)
the restore kernel will detect the compression algo in use anyway (or
at least it can be made do so), a modparam should work for this and it
would be far more convenient to use.

Second, if I can be convinced that indeed, using a kernel command line
option for this is the way to go, I don't particularly like the name
used in that patch.

Please feel free to send a replacement for patch [4/4] separately.

Thanks!