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Remove KMC_KMEM and KMC_VMEM

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`KMC_KMEM` and `KMC_VMEM` are now unused since all SPL-implemented
caches are `KMC_KVMEM`.

KMC_KMEM: Given the default value of `spl_kmem_cache_kmem_limit`, we
don't use kmalloc to back the SPL caches, instead we use kvmalloc
(KMC_KVMEM).  The flag, module parameter, /proc entries, and associated
code are removed.

KMC_VMEM: This flag is not used, and kvmalloc() is always preferable to
vmalloc().  The flag, /proc entries, and associated code are removed.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #10673
This commit is contained in:
Matthew Ahrens
2020-08-17 16:04:28 -07:00
committed by GitHub
parent 3df0c2fa32
commit 994de7e4b7
5 changed files with 10 additions and 151 deletions
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man/man5/spl-module-parameters.5
-31
View File
@@ -131,37 +131,6 @@ cutoff of 16K was determined to be optimal for architectures using 4K pages.
Default value: \fB16,384\fR
.RE
.sp
.ne 2
.na
\fBspl_kmem_cache_kmem_limit\fR (uint)
.ad
.RS 12n
Depending on the size of a cache object it may be backed by kmalloc()'d
or vmalloc()'d memory. This is because the size of the required allocation
greatly impacts the best way to allocate the memory.
.sp
When objects are small and only a small number of memory pages need to be
allocated, ideally just one, then kmalloc() is very efficient. However,
when allocating multiple pages with kmalloc() it gets increasingly expensive
because the pages must be physically contiguous.
.sp
For this reason we shift to vmalloc() for slabs of large objects which
which removes the need for contiguous pages. We cannot use vmalloc() in
all cases because there is significant locking overhead involved. This
function takes a single global lock over the entire virtual address range
which serializes all allocations. Using slightly different allocation
functions for small and large objects allows us to handle a wide range of
object sizes.
.sp
The \fBspl_kmem_cache_kmem_limit\fR value is used to determine this cutoff
size. One quarter the PAGE_SIZE is used as the default value because
\fBspl_kmem_cache_obj_per_slab\fR defaults to 16. This means that at
most we will need to allocate four contiguous pages.
.sp
Default value: \fBPAGE_SIZE/4\fR
.RE
.sp
.ne 2
.na