[PATCH 0/2] crypto: use vmalloc() for large stream workspaces

[Usama Arif <usama.arif@linux.dev>]

The zstd and deflate acomp implementations retain per-CPU stream
workspaces until the algorithms are unregistered. On x86-64 with 4 KiB
pages, kvmalloc() can back them with order-9 and order-6 kmalloc()
blocks, respectively.

Use vmalloc() and vfree() instead. For a server with 384 CPUs, if
we have streams on all of the CPUs and kvmalloc() takes the
kmalloc() path for every stream, their workspaces use 193.5 MiB more
for zstd and 42 MiB for deflate.

In five before/after boot pairs on a 96-vCPU x86-64 VM with 8 GiB RAM,
the test populated both algorithms crypto workspaces on every CPU. All
192 baseline workspaces used kmalloc() without these patches. The patches
reduced workspace backing by 48.375 MiB for zstd and 10.5 MiB for deflate
—58.875 MiB combined—in each pair.

In five before/after runs in a 4-vCPU x86-64 VM, median compression
and decompression throughput changed by less than 1% (-0.93% to +0.64%).
Inputs were 4 KiB and 64 KiB synthetic buffers containing pseudorandom
data or a 50/50 mix of repeating-pattern and pseudorandom bytes.
The differences were within the observed run-to-run variation.
 
Usama Arif (2):
  crypto: zstd - use vmalloc() for stream workspaces
  crypto: deflate - use vmalloc() for stream workspaces

 crypto/deflate.c | 5 +++--
 crypto/zstd.c    | 4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

-- 
2.53.0-Meta