include/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  *  For details, see <http://zfsonlinux.org/>.
  10  *
  11  *  The SPL is free software; you can redistribute it and/or modify it
  12  *  under the terms of the GNU General Public License as published by the
  13  *  Free Software Foundation; either version 2 of the License, or (at your
  14  *  option) any later version.
  15  *
  16  *  The SPL is distributed in the hope that it will be useful, but WITHOUT
  17  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  18  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  19  *  for more details.
  20  *
  21  *  You should have received a copy of the GNU General Public License along
  22  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
  23  */
  24
  25 #ifndef _SPL_VMEM_H
  26 #define _SPL_VMEM_H
  27
  28 #include <sys/kmem.h>
  29 #include <linux/sched.h>
  30 #include <linux/vmalloc.h>
  31
  32 typedef struct vmem { } vmem_t;
  33
  34 extern vmem_t *heap_arena;
  35 extern vmem_t *zio_alloc_arena;
  36 extern vmem_t *zio_arena;
  37
  38 extern size_t vmem_size(vmem_t *vmp, int typemask);
  39 extern void *spl_vmalloc(unsigned long size, gfp_t lflags, pgprot_t prot);
  40
  41 /*
  42  * Memory allocation interfaces
  43  */
  44 #define VMEM_ALLOC      0x01
  45 #define VMEM_FREE       0x02
  46
  47 #ifndef VMALLOC_TOTAL
  48 #define VMALLOC_TOTAL   (VMALLOC_END - VMALLOC_START)
  49 #endif
  50
  51 /*
  52  * vmem_* is an interface to a low level arena-based memory allocator on
  53  * Illumos that is used to allocate virtual address space. The kmem SLAB
  54  * allocator allocates slabs from it. Then the generic allocation functions
  55  * kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
  56  *
  57  * On Linux, the primary means of doing allocations is via kmalloc(), which
  58  * is similarly layered on top of something called the buddy allocator. The
  59  * buddy allocator is not available to kernel modules, it uses physical
  60  * memory addresses rather than virtual memory addresses and is prone to
  61  * fragmentation.
  62  *
  63  * Linux sets aside a relatively small address space for in-kernel virtual
  64  * memory from which allocations can be done using vmalloc().  It might seem
  65  * like a good idea to use vmalloc() to implement something similar to
  66  * Illumos' allocator. However, this has the following problems:
  67  *
  68  * 1. Page directory table allocations are hard coded to use GFP_KERNEL.
  69  *    Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
  70  *    vmalloc() will not have proper semantics.
  71  *
  72  * 2. Address space exhaustion is a real issue on 32-bit platforms where
  73  *    only a few 100MB are available. The kernel will handle it by spinning
  74  *    when it runs out of address space.
  75  *
  76  * 3. All vmalloc() allocations and frees are protected by a single global
  77  *    lock which serializes all allocations.
  78  *
  79  * 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
  80  *    list. The former will sum the allocations while the latter will print
  81  *    them to user space in a way that user space can keep the lock held
  82  *    indefinitely.  When the total number of mapped allocations is large
  83  *    (several 100,000) a large amount of time will be spent waiting on locks.
  84  *
  85  * 5. Linux has a wait_on_bit() locking primitive that assumes physical
  86  *    memory is used, it simply does not work on virtual memory.  Certain
  87  *    Linux structures (e.g. the superblock) use them and might be embedded
  88  *    into a structure from Illumos.  This makes using Linux virtual memory
  89  *    unsafe in certain situations.
  90  *
  91  * It follows that we cannot obtain identical semantics to those on Illumos.
  92  * Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
  93  * such a way that they can be used as drop-in replacements for small vmem_*
  94  * allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
  95  * to them.
  96  */
  97
  98 #define vmem_alloc(sz, fl)      spl_vmem_alloc((sz), (fl), __func__, __LINE__)
  99 #define vmem_zalloc(sz, fl)     spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
 100 #define vmem_free(ptr, sz)      spl_vmem_free((ptr), (sz))
 101 #define vmem_qcache_reap(ptr)   ((void)0)
 102
 103 extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line);
 104 extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line);
 105 extern void spl_vmem_free(const void *ptr, size_t sz);
 106
 107 int spl_vmem_init(void);
 108 void spl_vmem_fini(void);
 109
 110 #endif  /* _SPL_VMEM_H */