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