2013-11-18 13:46:10 +00:00
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'\" te
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.\"
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.\" Copyright 2013 Turbo Fredriksson <turbo@bayour.com>. All rights reserved.
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.\"
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.TH SPL-MODULE-PARAMETERS 5 "Nov 18, 2013"
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.SH NAME
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spl\-module\-parameters \- SPL module parameters
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.SH DESCRIPTION
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.sp
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.LP
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Description of the different parameters to the SPL module.
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.SS "Module parameters"
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.sp
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.LP
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_expire\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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Cache expiration is part of default Illumos cache behavior. The idea is
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that objects in magazines which have not been recently accessed should be
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returned to the slabs periodically. This is known as cache aging and
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when enabled objects will be typically returned after 15 seconds.
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.sp
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On the other hand Linux slabs are designed to never move objects back to
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the slabs unless there is memory pressure. This is possible because under
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Linux the cache will be notified when memory is low and objects can be
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released.
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.sp
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By default only the Linux method is enabled. It has been shown to improve
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responsiveness on low memory systems and not negatively impact the performance
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of systems with more memory. This policy may be changed by setting the
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\fBspl_kmem_cache_expire\fR bit mask as follows, both policies may be enabled
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concurrently.
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.sp
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0x01 - Aging (Illumos), 0x02 - Low memory (Linux)
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2013-11-18 13:46:10 +00:00
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.sp
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2014-12-05 23:31:24 +00:00
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Default value: \fB0x02\fR
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2013-11-18 13:46:10 +00:00
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.RE
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_reclaim\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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When this is set it prevents Linux from being able to rapidly reclaim all the
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memory held by the kmem caches. This may be useful in circumstances where
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it's preferable that Linux reclaim memory from some other subsystem first.
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Setting this will increase the likelihood out of memory events on a memory
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constrained system.
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2013-11-18 13:46:10 +00:00
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.sp
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2014-12-05 23:31:24 +00:00
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Default value: \fB0\fR
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2013-11-18 13:46:10 +00:00
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.RE
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_obj_per_slab\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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The preferred number of objects per slab in the cache. In general, a larger
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value will increase the caches memory footprint while decreasing the time
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required to perform an allocation. Conversely, a smaller value will minimize
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the footprint and improve cache reclaim time but individual allocations may
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take longer.
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2013-11-18 13:46:10 +00:00
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.sp
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Refine slab cache sizing
This change is designed to improve the memory utilization of
slabs by more carefully setting their size. The way the code
currently works is problematic for slabs which contain large
objects (>1MB). This is due to slabs being unconditionally
rounded up to a power of two which may result in unused space
at the end of the slab.
The reason the existing code rounds up every slab is because it
assumes it will backed by the buddy allocator. Since the buddy
allocator can only performs power of two allocations this is
desirable because it avoids wasting any space. However, this
logic breaks down if slab is backed by vmalloc() which operates
at a page level granularity. In this case, the optimal thing to
do is calculate the minimum required slab size given certain
constraints (object size, alignment, objects/slab, etc).
Therefore, this patch reworks the spl_slab_size() function so
that it sizes KMC_KMEM slabs differently than KMC_VMEM slabs.
KMC_KMEM slabs are rounded up to the nearest power of two, and
KMC_VMEM slabs are allowed to be the minimum required size.
This change also reduces the default number of objects per slab.
This reduces how much memory a single cache object can pin, which
can result in significant memory saving for highly fragmented
caches. But depending on the workload it may result in slabs
being allocated and freed more frequently. In practice, this
has been shown to be a better default for most workloads.
Also the maximum slab size has been reduced to 4MB on 32-bit
systems. Due to the limited virtual address space it's critical
the we be as frugal as possible. A limit of 4M still lets us
reasonably comfortably allocate a limited number of 1MB objects.
Finally, the kmem:slab_small and kmem:slab_large SPLAT tests
were extended to provide better test coverage of various object
sizes and alignments. Caches are created with random parameters
and their basic functionality is verified by allocating several
slabs worth of objects.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-15 22:06:18 +00:00
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Default value: \fB8\fR
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2013-11-18 13:46:10 +00:00
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.RE
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_obj_per_slab_min\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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The minimum number of objects allowed per slab. Normally slabs will contain
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\fBspl_kmem_cache_obj_per_slab\fR objects but for caches that contain very
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large objects it's desirable to only have a few, or even just one, object per
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slab.
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2013-11-18 13:46:10 +00:00
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.sp
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2014-12-05 23:31:24 +00:00
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Default value: \fB1\fR
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2013-11-18 13:46:10 +00:00
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.RE
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_max_size\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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The maximum size of a kmem cache slab in MiB. This effectively limits
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the maximum cache object size to \fBspl_kmem_cache_max_size\fR /
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\fBspl_kmem_cache_obj_per_slab\fR. Caches may not be created with
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object sized larger than this limit.
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2013-11-18 13:46:10 +00:00
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.sp
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Refine slab cache sizing
This change is designed to improve the memory utilization of
slabs by more carefully setting their size. The way the code
currently works is problematic for slabs which contain large
objects (>1MB). This is due to slabs being unconditionally
rounded up to a power of two which may result in unused space
at the end of the slab.
The reason the existing code rounds up every slab is because it
assumes it will backed by the buddy allocator. Since the buddy
allocator can only performs power of two allocations this is
desirable because it avoids wasting any space. However, this
logic breaks down if slab is backed by vmalloc() which operates
at a page level granularity. In this case, the optimal thing to
do is calculate the minimum required slab size given certain
constraints (object size, alignment, objects/slab, etc).
Therefore, this patch reworks the spl_slab_size() function so
that it sizes KMC_KMEM slabs differently than KMC_VMEM slabs.
KMC_KMEM slabs are rounded up to the nearest power of two, and
KMC_VMEM slabs are allowed to be the minimum required size.
This change also reduces the default number of objects per slab.
This reduces how much memory a single cache object can pin, which
can result in significant memory saving for highly fragmented
caches. But depending on the workload it may result in slabs
being allocated and freed more frequently. In practice, this
has been shown to be a better default for most workloads.
Also the maximum slab size has been reduced to 4MB on 32-bit
systems. Due to the limited virtual address space it's critical
the we be as frugal as possible. A limit of 4M still lets us
reasonably comfortably allocate a limited number of 1MB objects.
Finally, the kmem:slab_small and kmem:slab_large SPLAT tests
were extended to provide better test coverage of various object
sizes and alignments. Caches are created with random parameters
and their basic functionality is verified by allocating several
slabs worth of objects.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-15 22:06:18 +00:00
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Default value: \fB32 (64-bit) or 4 (32-bit)\fR
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2013-11-18 13:46:10 +00:00
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.RE
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.sp
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.ne 2
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.na
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2014-12-05 23:31:24 +00:00
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\fBspl_kmem_cache_slab_limit\fR (uint)
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2013-11-18 13:46:10 +00:00
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.ad
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.RS 12n
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2014-12-05 23:31:24 +00:00
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For small objects the Linux slab allocator should be used to make the most
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efficient use of the memory. However, large objects are not supported by
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the Linux slab and therefore the SPL implementation is preferred. This
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value is used to determine the cutoff between a small and large object.
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.sp
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Objects of \fBspl_kmem_cache_slab_limit\fR or smaller will be allocated
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using the Linux slab allocator, large objects use the SPL allocator. A
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cutoff of 16K was determined to be optimal for architectures using 4K pages.
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2013-11-18 13:46:10 +00:00
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.sp
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2014-12-05 23:31:24 +00:00
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Default value: \fB16,384\fR
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.RE
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.sp
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.ne 2
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.na
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\fBspl_kmem_cache_kmem_limit\fR (uint)
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.ad
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.RS 12n
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Depending on the size of a cache object it may be backed by kmalloc()'d
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or vmalloc()'d memory. This is because the size of the required allocation
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greatly impacts the best way to allocate the memory.
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.sp
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When objects are small and only a small number of memory pages need to be
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allocated, ideally just one, then kmalloc() is very efficient. However,
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when allocating multiple pages with kmalloc() it gets increasingly expensive
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because the pages must be physically contiguous.
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.sp
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For this reason we shift to vmalloc() for slabs of large objects which
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which removes the need for contiguous pages. We cannot use vmalloc() in
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all cases because there is significant locking overhead involved. This
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function takes a single global lock over the entire virtual address range
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which serializes all allocations. Using slightly different allocation
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functions for small and large objects allows us to handle a wide range of
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object sizes.
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.sh
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The \fBspl_kmem_cache_kmem_limit\fR value is used to determine this cutoff
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size. One quarter the PAGE_SIZE is used as the default value because
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\fBspl_kmem_cache_obj_per_slab\fR defaults to 16. This means that at
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most we will need to allocate four contiguous pages.
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.sp
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Default value: \fBPAGE_SIZE/4\fR
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2013-11-18 13:46:10 +00:00
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.RE
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Refactor generic memory allocation interfaces
This patch achieves the following goals:
1. It replaces the preprocessor kmem flag to gfp flag mapping with
proper translation logic. This eliminates the potential for
surprises that were previously possible where kmem flags were
mapped to gfp flags.
2. It maps vmem_alloc() allocations to kmem_alloc() for allocations
sized less than or equal to the newly-added spl_kmem_alloc_max
parameter. This ensures that small allocations will not contend
on a single global lock, large allocations can still be handled,
and potentially limited virtual address space will not be squandered.
This behavior is entirely different than under Illumos due to
different memory management strategies employed by the respective
kernels. However, this functionally provides the semantics required.
3. The --disable-debug-kmem, --enable-debug-kmem (default), and
--enable-debug-kmem-tracking allocators have been unified in to
a single spl_kmem_alloc_impl() allocation function. This was
done to simplify the code and make it more maintainable.
4. Improve portability by exposing an implementation of the memory
allocations functions that can be safely used in the same way
they are used on Illumos. Specifically, callers may safely
use KM_SLEEP in contexts which perform filesystem IO. This
allows us to eliminate an entire class of Linux specific changes
which were previously required to avoid deadlocking the system.
This change will be largely transparent to existing callers but there
are a few caveats:
1. Because the headers were refactored and extraneous includes removed
callers may find they need to explicitly add additional #includes.
In particular, kmem_cache.h must now be explicitly includes to
access the SPL's kmem cache implementation. This behavior is
different from Illumos but it was done to avoid always masking
the Linux slab functions when kmem.h is included.
2. Callers, like Lustre, which made assumptions about the definitions
of KM_SLEEP, KM_NOSLEEP, and KM_PUSHPAGE will need to be updated.
Other callers such as ZFS which did not will not require changes.
3. KM_PUSHPAGE is no longer overloaded to imply GFP_NOIO. It retains
its original meaning of allowing allocations to access reserved
memory. KM_PUSHPAGE callers can be converted back to KM_SLEEP.
4. The KM_NODEBUG flags has been retired and the default warning
threshold increased to 32k.
5. The kmem_virt() functions has been removed. For callers which
need to distinguish between a physical and virtual address use
is_vmalloc_addr().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-08 20:37:14 +00:00
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.sp
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.ne 2
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.na
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\fBspl_kmem_alloc_warn\fR (uint)
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.ad
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.RS 12n
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As a general rule kmem_alloc() allocations should be small, preferably
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just a few pages since they must by physically contiguous. Therefore, a
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rate limited warning will be printed to the console for any kmem_alloc()
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which exceeds a reasonable threshold.
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2014-12-05 23:31:24 +00:00
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.sp
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Refactor generic memory allocation interfaces
This patch achieves the following goals:
1. It replaces the preprocessor kmem flag to gfp flag mapping with
proper translation logic. This eliminates the potential for
surprises that were previously possible where kmem flags were
mapped to gfp flags.
2. It maps vmem_alloc() allocations to kmem_alloc() for allocations
sized less than or equal to the newly-added spl_kmem_alloc_max
parameter. This ensures that small allocations will not contend
on a single global lock, large allocations can still be handled,
and potentially limited virtual address space will not be squandered.
This behavior is entirely different than under Illumos due to
different memory management strategies employed by the respective
kernels. However, this functionally provides the semantics required.
3. The --disable-debug-kmem, --enable-debug-kmem (default), and
--enable-debug-kmem-tracking allocators have been unified in to
a single spl_kmem_alloc_impl() allocation function. This was
done to simplify the code and make it more maintainable.
4. Improve portability by exposing an implementation of the memory
allocations functions that can be safely used in the same way
they are used on Illumos. Specifically, callers may safely
use KM_SLEEP in contexts which perform filesystem IO. This
allows us to eliminate an entire class of Linux specific changes
which were previously required to avoid deadlocking the system.
This change will be largely transparent to existing callers but there
are a few caveats:
1. Because the headers were refactored and extraneous includes removed
callers may find they need to explicitly add additional #includes.
In particular, kmem_cache.h must now be explicitly includes to
access the SPL's kmem cache implementation. This behavior is
different from Illumos but it was done to avoid always masking
the Linux slab functions when kmem.h is included.
2. Callers, like Lustre, which made assumptions about the definitions
of KM_SLEEP, KM_NOSLEEP, and KM_PUSHPAGE will need to be updated.
Other callers such as ZFS which did not will not require changes.
3. KM_PUSHPAGE is no longer overloaded to imply GFP_NOIO. It retains
its original meaning of allowing allocations to access reserved
memory. KM_PUSHPAGE callers can be converted back to KM_SLEEP.
4. The KM_NODEBUG flags has been retired and the default warning
threshold increased to 32k.
5. The kmem_virt() functions has been removed. For callers which
need to distinguish between a physical and virtual address use
is_vmalloc_addr().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-08 20:37:14 +00:00
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The default warning threshold is set to eight pages but capped at 32K to
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accommodate systems using large pages. This value was selected to be small
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enough to ensure the largest allocations are quickly noticed and fixed.
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But large enough to avoid logging any warnings when a allocation size is
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larger than optimal but not a serious concern. Since this value is tunable,
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developers are encouraged to set it lower when testing so any new largish
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allocations are quickly caught. These warnings may be disabled by setting
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the threshold to zero.
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.sp
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2014-12-05 23:31:24 +00:00
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|
Default value: \fB32,768\fR
|
Refactor generic memory allocation interfaces
This patch achieves the following goals:
1. It replaces the preprocessor kmem flag to gfp flag mapping with
proper translation logic. This eliminates the potential for
surprises that were previously possible where kmem flags were
mapped to gfp flags.
2. It maps vmem_alloc() allocations to kmem_alloc() for allocations
sized less than or equal to the newly-added spl_kmem_alloc_max
parameter. This ensures that small allocations will not contend
on a single global lock, large allocations can still be handled,
and potentially limited virtual address space will not be squandered.
This behavior is entirely different than under Illumos due to
different memory management strategies employed by the respective
kernels. However, this functionally provides the semantics required.
3. The --disable-debug-kmem, --enable-debug-kmem (default), and
--enable-debug-kmem-tracking allocators have been unified in to
a single spl_kmem_alloc_impl() allocation function. This was
done to simplify the code and make it more maintainable.
4. Improve portability by exposing an implementation of the memory
allocations functions that can be safely used in the same way
they are used on Illumos. Specifically, callers may safely
use KM_SLEEP in contexts which perform filesystem IO. This
allows us to eliminate an entire class of Linux specific changes
which were previously required to avoid deadlocking the system.
This change will be largely transparent to existing callers but there
are a few caveats:
1. Because the headers were refactored and extraneous includes removed
callers may find they need to explicitly add additional #includes.
In particular, kmem_cache.h must now be explicitly includes to
access the SPL's kmem cache implementation. This behavior is
different from Illumos but it was done to avoid always masking
the Linux slab functions when kmem.h is included.
2. Callers, like Lustre, which made assumptions about the definitions
of KM_SLEEP, KM_NOSLEEP, and KM_PUSHPAGE will need to be updated.
Other callers such as ZFS which did not will not require changes.
3. KM_PUSHPAGE is no longer overloaded to imply GFP_NOIO. It retains
its original meaning of allowing allocations to access reserved
memory. KM_PUSHPAGE callers can be converted back to KM_SLEEP.
4. The KM_NODEBUG flags has been retired and the default warning
threshold increased to 32k.
5. The kmem_virt() functions has been removed. For callers which
need to distinguish between a physical and virtual address use
is_vmalloc_addr().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-08 20:37:14 +00:00
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|
.RE
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.sp
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.ne 2
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.na
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\fBspl_kmem_alloc_max\fR (uint)
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.ad
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.RS 12n
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|
Large kmem_alloc() allocations will fail if they exceed KMALLOC_MAX_SIZE.
|
|
|
|
|
Allocations which are marginally smaller than this limit may succeed but
|
|
|
|
|
should still be avoided due to the expense of locating a contiguous range
|
|
|
|
|
of free pages. Therefore, a maximum kmem size with reasonable safely
|
|
|
|
|
margin of 4x is set. Kmem_alloc() allocations larger than this maximum
|
|
|
|
|
will quickly fail. Vmem_alloc() allocations less than or equal to this
|
|
|
|
|
value will use kmalloc(), but shift to vmalloc() when exceeding this value.
|
|
|
|
|
.sp
|
2014-12-05 23:31:24 +00:00
|
|
|
Default value: \fBKMALLOC_MAX_SIZE/4\fR
|
Refactor generic memory allocation interfaces
This patch achieves the following goals:
1. It replaces the preprocessor kmem flag to gfp flag mapping with
proper translation logic. This eliminates the potential for
surprises that were previously possible where kmem flags were
mapped to gfp flags.
2. It maps vmem_alloc() allocations to kmem_alloc() for allocations
sized less than or equal to the newly-added spl_kmem_alloc_max
parameter. This ensures that small allocations will not contend
on a single global lock, large allocations can still be handled,
and potentially limited virtual address space will not be squandered.
This behavior is entirely different than under Illumos due to
different memory management strategies employed by the respective
kernels. However, this functionally provides the semantics required.
3. The --disable-debug-kmem, --enable-debug-kmem (default), and
--enable-debug-kmem-tracking allocators have been unified in to
a single spl_kmem_alloc_impl() allocation function. This was
done to simplify the code and make it more maintainable.
4. Improve portability by exposing an implementation of the memory
allocations functions that can be safely used in the same way
they are used on Illumos. Specifically, callers may safely
use KM_SLEEP in contexts which perform filesystem IO. This
allows us to eliminate an entire class of Linux specific changes
which were previously required to avoid deadlocking the system.
This change will be largely transparent to existing callers but there
are a few caveats:
1. Because the headers were refactored and extraneous includes removed
callers may find they need to explicitly add additional #includes.
In particular, kmem_cache.h must now be explicitly includes to
access the SPL's kmem cache implementation. This behavior is
different from Illumos but it was done to avoid always masking
the Linux slab functions when kmem.h is included.
2. Callers, like Lustre, which made assumptions about the definitions
of KM_SLEEP, KM_NOSLEEP, and KM_PUSHPAGE will need to be updated.
Other callers such as ZFS which did not will not require changes.
3. KM_PUSHPAGE is no longer overloaded to imply GFP_NOIO. It retains
its original meaning of allowing allocations to access reserved
memory. KM_PUSHPAGE callers can be converted back to KM_SLEEP.
4. The KM_NODEBUG flags has been retired and the default warning
threshold increased to 32k.
5. The kmem_virt() functions has been removed. For callers which
need to distinguish between a physical and virtual address use
is_vmalloc_addr().
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
2014-12-08 20:37:14 +00:00
|
|
|
.RE
|
|
|
|
|
|
2014-12-05 22:11:18 +00:00
|
|
|
.sp
|
|
|
|
|
.ne 2
|
|
|
|
|
.na
|
|
|
|
|
\fBspl_kmem_cache_magazine_size\fR (uint)
|
|
|
|
|
.ad
|
|
|
|
|
.RS 12n
|
|
|
|
|
Cache magazines are an optimization designed to minimize the cost of
|
|
|
|
|
allocating memory. They do this by keeping a per-cpu cache of recently
|
|
|
|
|
freed objects, which can then be reallocated without taking a lock. This
|
|
|
|
|
can improve performance on highly contended caches. However, because
|
|
|
|
|
objects in magazines will prevent otherwise empty slabs from being
|
|
|
|
|
immediately released this may not be ideal for low memory machines.
|
|
|
|
|
.sp
|
|
|
|
|
For this reason \fBspl_kmem_cache_magazine_size\fR can be used to set a
|
|
|
|
|
maximum magazine size. When this value is set to 0 the magazine size will
|
|
|
|
|
be automatically determined based on the object size. Otherwise magazines
|
|
|
|
|
will be limited to 2-256 objects per magazine (i.e per cpu). Magazines
|
|
|
|
|
may never be entirely disabled in this implementation.
|
|
|
|
|
.sp
|
2014-12-05 23:31:24 +00:00
|
|
|
Default value: \fB0\fR
|
2014-12-05 22:11:18 +00:00
|
|
|
.RE
|
|
|
|
|
|
2013-11-18 13:46:10 +00:00
|
|
|
.sp
|
|
|
|
|
.ne 2
|
|
|
|
|
.na
|
|
|
|
|
\fBspl_hostid\fR (ulong)
|
|
|
|
|
.ad
|
|
|
|
|
.RS 12n
|
2014-12-05 23:31:24 +00:00
|
|
|
The system hostid, when set this can be used to uniquely identify a system.
|
|
|
|
|
By default this value is set to zero which indicates the hostid is disabled.
|
|
|
|
|
It can be explicitly enabled by placing a unique non-zero value in
|
|
|
|
|
\fB/etc/hostid/\fR.
|
2013-11-18 13:46:10 +00:00
|
|
|
.sp
|
2014-12-05 23:31:24 +00:00
|
|
|
Default value: \fB0\fR
|
2013-11-18 13:46:10 +00:00
|
|
|
.RE
|
|
|
|
|
|
|
|
|
|
.sp
|
|
|
|
|
.ne 2
|
|
|
|
|
.na
|
|
|
|
|
\fBspl_hostid_path\fR (charp)
|
|
|
|
|
.ad
|
|
|
|
|
.RS 12n
|
2014-12-05 23:31:24 +00:00
|
|
|
The expected path to locate the system hostid when specified. This value
|
|
|
|
|
may be overridden for non-standard configurations.
|
2013-11-18 13:46:10 +00:00
|
|
|
.sp
|
2014-12-05 23:31:24 +00:00
|
|
|
Default value: \fB/etc/hostid\fR
|
2013-11-18 13:46:10 +00:00
|
|
|
.RE
|
|
|
|
|
|
2013-08-28 02:09:25 +00:00
|
|
|
.sp
|
|
|
|
|
.ne 2
|
|
|
|
|
.na
|
|
|
|
|
\fBspl_taskq_thread_bind\fR (int)
|
|
|
|
|
.ad
|
|
|
|
|
.RS 12n
|
2014-12-05 23:31:24 +00:00
|
|
|
Bind taskq threads to specific CPUs. When enabled all taskq threads will
|
|
|
|
|
be distributed evenly over the available CPUs. By default, this behavior
|
|
|
|
|
is disabled to allow the Linux scheduler the maximum flexibility to determine
|
|
|
|
|
where a thread should run.
|
2013-08-28 02:09:25 +00:00
|
|
|
.sp
|
2014-12-05 23:31:24 +00:00
|
|
|
Default value: \fB0\fR
|
2013-08-28 02:09:25 +00:00
|
|
|
.RE
|
