1 files changed, 109 insertions, 0 deletions
diff --git a/include/os/linux/spl/sys/vmem.h b/include/os/linux/spl/sys/vmem.h
new file mode 100644
index 000000000..a9b12eeb9
--- /dev/null
+++ b/include/os/linux/spl/sys/vmem.h
@@ -0,0 +1,109 @@
+/*
+ *  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 <[email protected]>.
+ *  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;
+
+extern vmem_t *heap_arena;
+extern vmem_t *zio_alloc_arena;
+extern vmem_t *zio_arena;
+
+extern size_t vmem_size(vmem_t *vmp, int typemask);
+
+/*
+ * 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))
+#define	vmem_qcache_reap(ptr)	((void)0)
+
+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 */