Re: [PATCH 2/2] kcompressd: Add Kcompressd for accelerated zram compression

[Nhat Pham <nphamcs@gmail.com>]

On Fri, Mar 7, 2025 at 11:41 AM Barry Song <21cnbao@gmail.com> wrote:
>
> On Sat, Mar 8, 2025 at 1:02 AM Qun-Wei Lin <qun-wei.lin@mediatek.com> wrote:
> >
> > Introduced Kcompressd to offload zram page compression, improving
> > system efficiency by handling compression separately from memory
> > reclaiming. Added necessary configurations and dependencies.
> >
> > Signed-off-by: Qun-Wei Lin <qun-wei.lin@mediatek.com>
> > ---
> >  drivers/block/zram/Kconfig      |  11 ++
> >  drivers/block/zram/Makefile     |   3 +-
> >  drivers/block/zram/kcompressd.c | 340 ++++++++++++++++++++++++++++++++
> >  drivers/block/zram/kcompressd.h |  25 +++
> >  drivers/block/zram/zram_drv.c   |  22 ++-
> >  5 files changed, 397 insertions(+), 4 deletions(-)
> >  create mode 100644 drivers/block/zram/kcompressd.c
> >  create mode 100644 drivers/block/zram/kcompressd.h
> >
> > diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
> > index 402b7b175863..f0a1b574f770 100644
> > --- a/drivers/block/zram/Kconfig
> > +++ b/drivers/block/zram/Kconfig
> > @@ -145,3 +145,14 @@ config ZRAM_MULTI_COMP
> >           re-compress pages using a potentially slower but more effective
> >           compression algorithm. Note, that IDLE page recompression
> >           requires ZRAM_TRACK_ENTRY_ACTIME.
> > +
> > +config KCOMPRESSD
> > +       tristate "Kcompressd: Accelerated zram compression"
> > +       depends on ZRAM
> > +       help
> > +         Kcompressd creates multiple daemons to accelerate the compression of pages
> > +         in zram, offloading this time-consuming task from the zram driver.
> > +
> > +         This approach improves system efficiency by handling page compression separately,
> > +         which was originally done by kswapd or direct reclaim.
>
> For direct reclaim, we were previously able to compress using multiple CPUs
> with multi-threading.
> After your patch, it seems that only a single thread/CPU is used for compression
> so it won't necessarily improve direct reclaim performance?
>
> Even for kswapd, we used to have multiple threads like [kswapd0], [kswapd1],
> and [kswapd2] for different nodes. Now, are we also limited to just one thread?
> I also wonder if this could be handled at the vmscan level instead of the zram
> level. then it might potentially help other sync devices or even zswap later.

Agree. A shared solution would be much appreciated. We can keep the
kcompressd idea, but have it accept IO work from multiple sources
(zram, zswap, whatever) through a shared API.

Otherwise we would need to reinvent the wheel multiple times :)