The workspace required by zlib to perform compression is roughly
512MB (order-7). These allocations are so large that we should
never attempt to directly kmalloc an emergency object for them.
It is far preferable to asynchronously vmalloc an additional slab
in case it's needed. Then simply block waiting for an existing
object to be released or for the new slab to be allocated.
This can be accomplished by disabling emergency slab objects by
passing the KMC_NOEMERGENCY flag at slab creation time.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
zfsonlinux/zfs#917
This is a bit of cleanup I'd been meaning to get to for a while
to reduce the chance of a type conflict. Well that conflict
finally occurred with the kstat_init() function which conflicts
with a function in the 2.6.32-6-pve kernel.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#56
The function zlib_deflate_workspacesize() now take 2 arguments.
This was done to avoid always having to allocate the maximum size
workspace (268K). The caller can now specific the windowBits and
memLevel compression parameters to get a smaller workspace.
For our purposes we introduce a spl_zlib_deflate_workspacesize()
wrapper which accepts both arguments. When the two argument
version of zlib_deflate_workspacesize() is available the arguments
are passed through. When it's not we assume the worst case and
a maximally sized workspace is used.
While portions of the code needed to support z_compress_level() and
z_uncompress() where in place. In reality the current implementation
was non-functional, it just was compilable.
The critical missing component was to setup a workspace for the
compress/uncompress stream structures to use. A kmem_cache was
added for the workspace area because we require a large chunk
of memory. This avoids to need to continually alloc/free this
memory and vmap() the pages which is very slow. Several objects
will reside in the per-cpu kmem_cache making them quick to acquire
and release. A further optimization would be to adjust the
implementation to additional ensure the memory is local to the cpu.
Currently that may not be the case.
Brian Behlendorf