include/os/linux/spl/sys/vmem.h

   1 /*
   2  *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
   3  *  Copyright (C) 2007 The Regents of the University of California.
   4  *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
   5  *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
   6  *  UCRL-CODE-235197
   7  *
   8  *  This file is part of the SPL, Solaris Porting Layer.
   9  *
  10  *  The SPL is free software; you can redistribute it and/or modify it
  11  *  under the terms of the GNU General Public License as published by the
  12  *  Free Software Foundation; either version 2 of the License, or (at your
  13  *  option) any later version.
  14  *
  15  *  The SPL is distributed in the hope that it will be useful, but WITHOUT
  16  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  17  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  18  *  for more details.
  19  *
  20  *  You should have received a copy of the GNU General Public License along
  21  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
  22  */
  23
  24 #ifndef _SPL_VMEM_H
  25 #define _SPL_VMEM_H
  26
  27 #include <sys/kmem.h>
  28 #include <linux/sched.h>
  29 #include <linux/vmalloc.h>
  30
  31 typedef struct vmem { } vmem_t;
  32
  33 /*
  34  * Memory allocation interfaces
  35  */
  36 #define VMEM_ALLOC      0x01
  37 #define VMEM_FREE       0x02
  38
  39 #ifndef VMALLOC_TOTAL
  40 #define VMALLOC_TOTAL   (VMALLOC_END - VMALLOC_START)
  41 #endif
  42
  43 /*
  44  * vmem_* is an interface to a low level arena-based memory allocator on
  45  * Illumos that is used to allocate virtual address space. The kmem SLAB
  46  * allocator allocates slabs from it. Then the generic allocation functions
  47  * kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
  48  *
  49  * On Linux, the primary means of doing allocations is via kmalloc(), which
  50  * is similarly layered on top of something called the buddy allocator. The
  51  * buddy allocator is not available to kernel modules, it uses physical
  52  * memory addresses rather than virtual memory addresses and is prone to
  53  * fragmentation.
  54  *
  55  * Linux sets aside a relatively small address space for in-kernel virtual
  56  * memory from which allocations can be done using vmalloc().  It might seem
  57  * like a good idea to use vmalloc() to implement something similar to
  58  * Illumos' allocator. However, this has the following problems:
  59  *
  60  * 1. Page directory table allocations are hard coded to use GFP_KERNEL.
  61  *    Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
  62  *    vmalloc() will not have proper semantics.
  63  *
  64  * 2. Address space exhaustion is a real issue on 32-bit platforms where
  65  *    only a few 100MB are available. The kernel will handle it by spinning
  66  *    when it runs out of address space.
  67  *
  68  * 3. All vmalloc() allocations and frees are protected by a single global
  69  *    lock which serializes all allocations.
  70  *
  71  * 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
  72  *    list. The former will sum the allocations while the latter will print
  73  *    them to user space in a way that user space can keep the lock held
  74  *    indefinitely.  When the total number of mapped allocations is large
  75  *    (several 100,000) a large amount of time will be spent waiting on locks.
  76  *
  77  * 5. Linux has a wait_on_bit() locking primitive that assumes physical
  78  *    memory is used, it simply does not work on virtual memory.  Certain
  79  *    Linux structures (e.g. the superblock) use them and might be embedded
  80  *    into a structure from Illumos.  This makes using Linux virtual memory
  81  *    unsafe in certain situations.
  82  *
  83  * It follows that we cannot obtain identical semantics to those on Illumos.
  84  * Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
  85  * such a way that they can be used as drop-in replacements for small vmem_*
  86  * allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
  87  * to them.
  88  */
  89
  90 #define vmem_alloc(sz, fl)      spl_vmem_alloc((sz), (fl), __func__, __LINE__)
  91 #define vmem_zalloc(sz, fl)     spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
  92 #define vmem_free(ptr, sz)      spl_vmem_free((ptr), (sz))
  93
  94 extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line);
  95 extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line);
  96 extern void spl_vmem_free(const void *ptr, size_t sz);
  97
  98 int spl_vmem_init(void);
  99 void spl_vmem_fini(void);
 100
 101 #endif  /* _SPL_VMEM_H */