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

[Nikhil V]

On 1/31/2024 7:50 PM, Rafael J. Wysocki wrote:
> 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!

Hi @Rafael,

Thanks for the update.

Regarding patch[4/4], will work on modifying the code as mentioned by 
adding module parameter instead of kernel cmdline parameter. Will send a 
separate patch for this after testing with the changes. Thanks for the 
input.

Thanks,
Nikhil V