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UVM_HOTPLUG(9) Kernel Developer's Manual UVM_HOTPLUG(9)
NAME
uvm_physseg_init, uvm_physseg_valid_p, uvm_physseg_get_start,
uvm_physseg_get_end, uvm_physseg_get_avail_start,
uvm_physseg_get_avail_end, uvm_physseg_get_pg, uvm_physseg_get_pmseg,
uvm_physseg_get_free_list, uvm_physseg_get_start_hint,
uvm_physseg_set_start_hint, uvm_physseg_get_next, uvm_physseg_get_prev,
uvm_physseg_get_first, uvm_physseg_get_last,
uvm_physseg_get_highest_frame, uvm_physseg_find, uvm_page_physload,
uvm_page_physunload, uvm_page_physunload_force, uvm_physseg_plug,
uvm_physseg_unplug, uvm_physseg_set_avail_start,
uvm_physseg_set_avail_end - memory hotplug manager
SYNOPSIS
#include <uvm/uvm_physseg.h>
void
uvm_physseg_init(void);
uvm_physseg_t
uvm_page_physload(paddr_t start, paddr_t end, paddr_t avail_start,
paddr_t avail_end, int free_list);
bool
uvm_page_physunload(uvm_physseg_t upm, int free_list, paddr_t *paddrp);
bool
uvm_page_physunload_force(uvm_physseg_t upm, int free_list,
paddr_t *paddrp);
bool
uvm_physseg_plug(paddr_t pfn, size_t npages, uvm_physseg_t *upmp);
bool
uvm_physseg_unplug(paddr_t pfn, size_t npages);
DESCRIPTION
These utility routines provide the ability to tell uvm(9) about system
memory segments. When the kernel is compiled with 'options UVM_HOTPLUG',
memory segments are handled in a dynamic data structure (rbtree(3))
compared to a static array when not. This enables kernel code to add or
remove information about memory segments at any point after boot - thus
"hotplug".
uvm_page_physload(), uvm_page_physunload(), and
uvm_page_physunload_force() are legacy interfaces which may be removed in
the future. They must never be used after uvm_init(9).
WARNING: This is an experimental feature and should not be used in
production environments. Furthermore, attempting to "hotplug" without
'options UVM_HOTPLUG' after boot will almost certainly end in a panic(9).
USAGE
INITIALIZING HOTPLUG
The function uvm_physseg_init() initializes the hotplug subsystem. This
is expected to happen exactly once, at boot time, and from MD code.
PLUGGING IN MEMORY
uvm_page_physload() registers uvm(9) with a memory segment span, and on a
specified free_list. It must be called at system boot time as part of
setting up memory management. The arguments describe the start and end
of the physical addresses of the segment, and the available start and end
addresses of pages not already in use. If a system has memory banks of
different speeds the slower memory should be given a higher free_list
value.
start Starting page frame number of the physical memory
segments.
end Ending page frame number of the physical memory
segments.
avail_start Available starting page frame number of the physical
memory segments.
avail_end Available ending page frame number of the physical
memory segments.
free_list The free list types are defined in the Machine
Dependent code.
This function returns a valid uvm_physseg_t handle when a successful plug
occurs, else it will return UVM_PHYSSEG_TYPE_INVALID when the plug fails.
uvm_physseg_plug() registers uvm(9) with a memory segment span. It can
also be called to initiate a hotplug and register a newly "hotplugged"
physical memory range into the VM. Unlike uvm_page_physload() this
function can, if 'options UVM_HOTPLUG' is enabled at compile time, be
used after uvm_init(9). The arguments describe the start page frame, the
number of pages to plug starting from the start page frame and an
optional return variable, which points to a valid uvm_physseg_t handle
when a successful plug occurs.
pfn Starting page frame number of the physical memory segment.
npages Total number of pages from the starting page frame number
to plug in.
upmp If upmp is not NULL, then on a successful plug, a valid
pointer to the uvm_physseg_t handle for the segment which
was plugged is returned.
This function returns true when a successful plug occurs, false
otherwise.
UNPLUGGING MEMORY
The functions uvm_page_physunload(), uvm_page_physunload_force(), and
uvm_physseg_unplug() make uvm(9) forget about previously registered
memory segments or portions of such.
uvm_page_physunload() unloads pages from a segment (from the front or
from the back) depending on its availability. When the last page is
removed, the segment handle is invalidated and supporting metadata is
freed.
Note: This function can only be used during boot time. Pages, once
unloaded, are unregistered from uvm and are therefore assumed to be
managed by the code which called uvm_page_physunload(9) (usually boot
time MD code, for boottime memory "allocation").
The arguments are:
upm The handle identifying segment from which we are trying
to unload memory.
free_list The free list types are defined in the Machine Dependent
code.
paddrp The pointer to the physical address that was unloaded.
If the unload was successful, true is returned, false otherwise.
uvm_page_physunload_force() unconditionally unloads pages from a segment.
When the last page is removed, the segment handle is invalidated and
supporting metadata is freed.
Note: This function can only be used during boot time. Pages, once
unloaded, are unregistered from uvm and are therefore assumed to be
managed by the code which called uvm_page_physunload_force(9) (usually
boot time MD code, for boottime memory "allocation").
The arguments are:
upm The handle identifying segment from which we are trying
to unload memory.
free_list The free list types are defined in the Machine Dependent
code.
paddrp The pointer to the physical address that was unloaded.
If the unload was successful true is returned, false otherwise.
uvm_physseg_unplug() can be called to unplug an existing physical memory
segment. Unlike uvm_page_physunload() and uvm_page_physunload_force(),
it can be called after uvm_init(9), if 'options UVM_HOTPLUG' is enabled
at compile time. uvm_hotplug(9) makes no effort to manage the state of
the underlying physical memory. It is up to the caller to ensure that it
is not in use, either by uvm(9), or by any other sub-system. Further,
any hardware quiescing that may be required is the responsibility of MD
code. The arguments describe the start page frame and the number of
pages to unplug. The arguments are:
pfn Starting page frame number of the physical memory segment.
npages Total number of pages from the starting page frame number
to unplug.
Returns true or false depending on success or failure respectively.
UTILITY FUNCTIONS
bool
uvm_physseg_valid_p(uvm_physseg_t upm)
paddr_t
uvm_physseg_get_start(uvm_physseg_t upm)
paddr_t
uvm_physseg_get_end(uvm_physseg_t upm)
paddr_t
uvm_physseg_get_avail_start(uvm_physseg_t upm)
paddr_t
uvm_physseg_get_avail_end(uvm_physseg_t upm)
struct vm_page *
uvm_physseg_get_pg(uvm_physseg_t upm, paddr_t index)
struct pmap_physseg *
uvm_physseg_get_pmesg(uvm_physseg_t upm)
int
uvm_physseg_get_free_list(uvm_physseg_t upm)
u_int
uvm_physseg_get_start_hint(uvm_physseg_t upm)
bool
uvm_physseg_set_start_hint(uvm_physseg_t upm, u_int start_hint)
uvm_physseg_t
uvm_physseg_get_next(uvm_physseg_t upm)
uvm_physseg_t
uvm_physseg_get_prev(uvm_physseg_t upm)
uvm_physseg_t
uvm_physseg_get_first(void)
uvm_physseg_t
uvm_physseg_get_last(void)
paddr_t
uvm_physseg_get_highest_frame(void)
paddr_t
uvm_physseg_find(paddr pframe, psize_t *offsetp)
void
uvm_physseg_set_avail_start(uvm_physseg_t upm, paddr_t avail_start)
void
uvm_physseg_set_avail_end(uvm_physseg_t upm, paddr_t avail_end)
uvm_physseg_valid_p() validates a handle that is passed in, returns true
if the given handle is valid, false otherwise.
uvm_physseg_get_start() if a valid uvm_physseg_t handle is passed in, it
returns the starting physical address of the segment. The returned value
is of type paddr_t. In case the handle is invalid the returned value
will match (paddr_t) -1.
uvm_physseg_get_end() if a valid uvm_physseg_t handle is passed in, it
returns the ending physical address of the segment. The returned value
is of type paddr_t. In case the handle is invalid the returned value
will match (paddr_t) -1.
uvm_physseg_get_avail_start() if a valid uvm_physseg_t handle is passed
in, it returns the available starting physical address of the segment.
The returned value is of type paddr_t. In case the handle is invalid the
returned value will match (paddr_t) -1.
uvm_physseg_get_avail_end() if a valid uvm_physseg_t handle is passed in,
it returns the available ending physical address of the segment. The
returned value is of type paddr_t. In case the handle is invalid the
returned value will match (paddr_t) -1.
uvm_physseg_get_pg() if a valid uvm_physseg_t handle along with an index
value is passed in, it returns the struct vm_page * object contained in
that location.
uvm_physseg_get_pmseg() if a valid uvm_physseg_t handle is passed in, it
returns the struct pmap_physseg * object contained in the handle.
uvm_physseg_get_free_list() if a valid uvm_physseg_t handle is passed in,
it returns the free_list type for which the current segment is associated
with. The returned value is of type int.
uvm_physseg_get_start_hint() if a valid uvm_physseg_t handle is passed
in, it returns the start_hint type for the current segment. The returned
value is of type u_int.
uvm_physseg_set_start_hint() if a valid handle along with the start_hint
is passed in, the value is set in the segment. And a true is returned to
indicate a successful value setting. In case the handle is invalid a
false is returned.
uvm_physseg_get_next() if a valid handle is passed in, it returns the
next valid uvm_physseg_t handle in the sequence. However if the handle
passed is the last segment in the sequence the function returns
UVM_PHYSSEG_TYPE_INVALID_OVERFLOW. Passing an invalid handle is not
fatal, and returns UVM_PHYSSEG_TYPE_INVALID.
uvm_physseg_get_prev() if a valid handle is passed in, it returns the
previous validh uvm_physseg_t handle in the sequence. However if the
handle passed is the first segment in the sequence the function returns
UVM_PHYSSEG_TYPE_INVALID_EMPTY. Passing an invalid handle is not fatal,
and returns UVM_PHYSSEG_TYPE_INVALID.
uvm_physseg_get_first() returns the first valid uvm_physseg_t handle in
the sequence. However if there are no valid handles in the sequence yet,
the function returns UVM_PHYSSEG_TYPE_INVALID_EMPTY.
uvm_physseg_get_last() returns the last valid uvm_physseg_t handle in the
sequence. However if there are no valid handles in the sequence yet, the
function returns UVM_PHYSSEG_TYPE_INVALID_EMPTY.
uvm_physseg_get_highest_frame() returns the frame number of the highest
registered physical page frame which is of type paddr_t. XXX: Searching
on empty sequences are not yet processed in the function.
uvm_physseg_find() searches for a given segment containing the page frame
(paddr_t) passed in. If a segment that falls between starting and ending
addresses is found, the corresponding uvm_physseg_t handle is returned
else a UVM_PHYSSEG_TYPE_INVALID is returned. The second parameter, if
not set to NULL, the offset value of the page frame passed in with
respect to the starting address is set to the appropriate psize_t value
if the search was successful in finding the segment.
uvm_physseg_set_avail_start() if a valid uvm_physseg_t handle is passed
in along with the available starting physical address of the segment of
type paddr_t, the value is set in the segment.
uvm_physseg_set_avail_end() if a valid uvm_physseg_t handle is passed in
along with the available ending physical address of the segment of type
paddr_t, the value is set in the segment.
NOTES
uvm_physseg_plug() and uvm_physseg_unplug() must never be used after
uvm_init(9) in a kernel build where 'options UVM_HOTPLUG' is not enabled.
DIAGNOSTICS
Tests for uvm_physseg_init are in tests/sys/uvm.
Unit / functional tests are in tests/sys/uvm/t_uvm_physseg.c. These
tests focus on the expected working of the uvm_physseg_init API and its
utility functions.
Load tests can be found in tests/sys/uvm/t_uvm_physseg_load.c. These
tests focus on stressing the uvm_physseg_init implementation in order to
make performance comparisons between kernel builds with and without
'options UVM_HOTPLUG'
CODE REFERENCES
The uvm hotplug feature is implemented in the file sys/uvm/uvm_physseg.c.
The uvm hotplug API is exported via sys/uvm/uvm_physseg.h.
SEE ALSO
extent(9), free(9), malloc(9), memoryallocators(9), uvm(9)
HISTORY
This API emerged out of the need to insert new pages at runtime in the
Xen x86/balloon(4) driver.
AUTHORS
Cherry G. Mathew <cherry@NetBSD.org> designed and integrated the API.
Santhosh N. Raju <santhosh.raju@gmail.com> implemented the dynamic
segment handling code and all tests for this API.
Nick Hudson <skrll@NetBSD.org> contributed bugfixes and testing on a wide
range of hardware ports.
NetBSD 10.99 January 17, 2020 NetBSD 10.99