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32 .Nd "memory allocator for debugging purposes"
34 .Cd "options DEBUG_MEMGUARD"
37 is a simple and small replacement memory allocator designed
38 to help detect tamper-after-free scenarios.
39 These problems are more and more common and likely with
40 multithreaded kernels where race conditions are more prevalent.
49 for a single malloc type.
51 can also guard all allocations larger than
53 and can guard a random fraction of all allocations.
54 There is also a knob to prevent allocations smaller than a specified
55 size from being guarded, to limit memory waste.
59 for a memory type, either add an entry to
60 .Pa /boot/loader.conf :
61 .Bd -literal -offset indent
62 vm.memguard.desc=<memory_type>
69 .Bd -literal -offset indent
70 sysctl vm.memguard.desc=<memory_type>
75 is a short description of the memory type to monitor.
76 Only allocations from that
80 is set will potentially be guarded.
83 is modified at run-time then only allocations of the new
85 will potentially be guarded once the
88 Existing guarded allocations will still be properly released by
91 The short description of a
93 type is the second argument to
95 so one has to find it in the kernel source.
98 .Va vm.memguard.divisor
99 boot-time tunable is used to scale how much of the system's physical
102 is allowed to consume.
103 The default is 10, so up to
104 .Va cnt.v_page_count Ns /10
110 .Va vm.memguard.divisor
111 bytes of virtual address space, limited by twice the physical memory
113 The physical limit is reported as
114 .Va vm.memguard.phys_limit
115 and the virtual space reserved for
118 .Va vm.memguard.mapsize .
121 will not do page promotions for any allocation smaller than
122 .Va vm.memguard.minsize
124 The default is 0, meaning all allocations can potentially be guarded.
126 can guard sufficiently large allocations randomly, with average
127 frequency of every one in 100000 /
128 .Va vm.memguard.frequency
130 The default is 0, meaning no allocations are randomly guarded.
133 can optionally add unmapped guard pages around each allocation to
134 detect overflow and underflow, if
135 .Va vm.memguard.options
137 This option is enabled by default.
139 will optionally guard all allocations of
142 .Va vm.memguard.options
144 This option is off by default.
158 was originally written by
159 .An Bosko Milekic Aq bmilekic@FreeBSD.org .
160 This manual page was originally written by
161 .An Christian Brueffer Aq brueffer@FreeBSD.org .
162 Additions have been made by
163 .An Matthew Fleming Aq mdf@FreeBSD.org
164 to both the implementation and the documentation.
166 Currently, it is not possible to override UMA