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d0249a4bd0
This change updates the documentation to refer to the project as OpenZFS instead ZFS on Linux. Web links have been updated to refer to https://github.com/openzfs/zfs. The extraneous zfsonlinux.org web links in the ZED and SPL sources have been dropped. Reviewed-by: George Melikov <mail@gmelikov.ru> Reviewed-by: Richard Laager <rlaager@wiktel.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #11007
102 lines
4.2 KiB
C
102 lines
4.2 KiB
C
/*
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* Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
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* Copyright (C) 2007 The Regents of the University of California.
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* Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
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* Written by Brian Behlendorf <behlendorf1@llnl.gov>.
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* UCRL-CODE-235197
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*
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* This file is part of the SPL, Solaris Porting Layer.
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*
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* The SPL is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* option) any later version.
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*
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* The SPL is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with the SPL. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _SPL_VMEM_H
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#define _SPL_VMEM_H
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#include <sys/kmem.h>
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#include <linux/sched.h>
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#include <linux/vmalloc.h>
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typedef struct vmem { } vmem_t;
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/*
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* Memory allocation interfaces
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*/
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#define VMEM_ALLOC 0x01
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#define VMEM_FREE 0x02
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#ifndef VMALLOC_TOTAL
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#define VMALLOC_TOTAL (VMALLOC_END - VMALLOC_START)
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#endif
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/*
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* vmem_* is an interface to a low level arena-based memory allocator on
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* Illumos that is used to allocate virtual address space. The kmem SLAB
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* allocator allocates slabs from it. Then the generic allocation functions
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* kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
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*
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* On Linux, the primary means of doing allocations is via kmalloc(), which
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* is similarly layered on top of something called the buddy allocator. The
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* buddy allocator is not available to kernel modules, it uses physical
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* memory addresses rather than virtual memory addresses and is prone to
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* fragmentation.
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*
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* Linux sets aside a relatively small address space for in-kernel virtual
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* memory from which allocations can be done using vmalloc(). It might seem
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* like a good idea to use vmalloc() to implement something similar to
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* Illumos' allocator. However, this has the following problems:
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*
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* 1. Page directory table allocations are hard coded to use GFP_KERNEL.
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* Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
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* vmalloc() will not have proper semantics.
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*
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* 2. Address space exhaustion is a real issue on 32-bit platforms where
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* only a few 100MB are available. The kernel will handle it by spinning
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* when it runs out of address space.
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*
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* 3. All vmalloc() allocations and frees are protected by a single global
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* lock which serializes all allocations.
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*
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* 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
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* list. The former will sum the allocations while the latter will print
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* them to user space in a way that user space can keep the lock held
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* indefinitely. When the total number of mapped allocations is large
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* (several 100,000) a large amount of time will be spent waiting on locks.
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*
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* 5. Linux has a wait_on_bit() locking primitive that assumes physical
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* memory is used, it simply does not work on virtual memory. Certain
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* Linux structures (e.g. the superblock) use them and might be embedded
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* into a structure from Illumos. This makes using Linux virtual memory
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* unsafe in certain situations.
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*
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* It follows that we cannot obtain identical semantics to those on Illumos.
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* Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
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* such a way that they can be used as drop-in replacements for small vmem_*
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* allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
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* to them.
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*/
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#define vmem_alloc(sz, fl) spl_vmem_alloc((sz), (fl), __func__, __LINE__)
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#define vmem_zalloc(sz, fl) spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
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#define vmem_free(ptr, sz) spl_vmem_free((ptr), (sz))
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extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line);
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extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line);
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extern void spl_vmem_free(const void *ptr, size_t sz);
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int spl_vmem_init(void);
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void spl_vmem_fini(void);
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#endif /* _SPL_VMEM_H */
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