Re: [PATCH v7 00/15] zswap IAA compress batching

[Yosry Ahmed <yosry.ahmed@linux.dev>]

On Sat, Mar 01, 2025 at 01:09:22AM +0000, Sridhar, Kanchana P wrote:
> Hi All,
> 
> > Performance testing (Kernel compilation, allmodconfig):
> > =======================================================
> > 
> > The experiments with kernel compilation test, 32 threads, in tmpfs use the
> > "allmodconfig" that takes ~12 minutes, and has considerable swapout/swapin
> > activity. The cgroup's memory.max is set to 2G.
> > 
> > 
> >  64K folios: Kernel compilation/allmodconfig:
> >  ============================================
> > 
> >  -------------------------------------------------------------------------------
> >                      mm-unstable               v7   mm-unstable            v7
> >  -------------------------------------------------------------------------------
> >  zswap compressor    deflate-iaa      deflate-iaa          zstd          zstd
> >  -------------------------------------------------------------------------------
> >  real_sec                 775.83           765.90        769.39        772.63
> >  user_sec              15,659.10        15,659.14     15,666.28     15,665.98
> >  sys_sec                4,209.69         4,040.44      5,277.86      5,358.61
> >  -------------------------------------------------------------------------------
> >  Max_Res_Set_Size_KB   1,871,116        1,874,128     1,873,200     1,873,488
> >  -------------------------------------------------------------------------------
> >  memcg_high                    0                0             0             0
> >  memcg_swap_fail               0                0             0             0
> >  zswpout             107,305,181      106,985,511    86,621,912    89,355,274
> >  zswpin               32,418,991       32,184,517    25,337,514    26,522,042
> >  pswpout                     272               80            94            16
> >  pswpin                      274               69            54            16
> >  thp_swpout                    0                0             0             0
> >  thp_swpout_fallback           0                0             0             0
> >  64kB_swpout_fallback        494                0             0             0
> >  pgmajfault           34,577,545       34,333,290    26,892,991    28,132,682
> >  ZSWPOUT-64kB          3,498,796        3,460,751     2,737,544     2,823,211
> >  SWPOUT-64kB                  17                4             4             1
> >  -------------------------------------------------------------------------------
> > 
> > [...]
> >
> > Summary:
> > ========
> > The performance testing data with usemem 30 processes and kernel
> > compilation test show 61%-73% throughput gains and 27%-37% sys time
> > reduction (usemem30) and 4% sys time reduction (kernel compilation) with
> > zswap_store() large folios using IAA compress batching as compared to
> > IAA sequential. There is no performance regression for zstd/usemem30 and a
> > slight 1.5% sys time zstd regression with kernel compilation allmod
> > config.
> 
> I think I know why kernel_compilation with zstd shows a regression whereas
> usemem30 does not. It is because I lock/unlock the acomp_ctx mutex once
> per folio. This can cause decomp jobs to wait for the mutex, which can cause
> more compressions, and this repeats. kernel_compilation has 25M+ decomps
> with zstd, whereas usemem30 has practically no decomps, but is
> compression-intensive, because of which it benefits the once-per-folio lock
> acquire/release.
> 
> I am testing a fix where I return zswap_compress() to do the mutex lock/unlock,
> and expect to post v8 by end of the day. I would appreciate it if you can hold off
> on reviewing only the zswap patches [14, 15] in my v7 and instead review the v8
> versions of these two patches.

I was planning to take a look at v7 next week, so take your time, no
rush to post it on a Friday afternoon.

Anyway, thanks for the heads up, I appreciate you trying to save
everyone's time.