> -----Original Message-----
> From: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Sent: Wednesday, June 10, 2020 5:22 AM
> To: Williams, Dan J <dan.j.williams@xxxxxxxxx>
> Cc: Kaneda, Erik <erik.kaneda@xxxxxxxxx>; Wysocki, Rafael J
> <rafael.j.wysocki@xxxxxxxxx>; Len Brown <lenb@xxxxxxxxxx>; Borislav
> Petkov <bp@xxxxxxxxx>; Weiny, Ira <ira.weiny@xxxxxxxxx>; James Morse
> <james.morse@xxxxxxx>; Myron Stowe <myron.stowe@xxxxxxxxxx>;
> Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx; linux-
> nvdimm@xxxxxxxxxxxx; Moore, Robert <robert.moore@xxxxxxxxx>
> Subject: [RFT][PATCH 2/3] ACPICA: Remove unused memory mappings on
> interpreter exit
>
> From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
>
> For transient memory opregions that are created dynamically under
> the namespace and interpreter mutexes and go away quickly, there
> still is the problem that removing their memory mappings may take
> significant time and so doing that while holding the mutexes should
> be avoided.
>
> For example, unmapping a chunk of memory associated with a memory
> opregion in Linux involves running synchronize_rcu_expedited()
> which really should not be done with the namespace mutex held.
>
> To address that problem, notice that the unused memory mappings left
> behind by the "dynamic" opregions that went away need not be unmapped
> right away when the opregion is deactivated. Instead, they may be
> unmapped when exiting the interpreter, after the namespace and
> interpreter mutexes have been dropped (there's one more place dealing
> with opregions in the debug code that can be treated analogously).
>
> Accordingly, change acpi_ev_system_memory_region_setup() to put
> the unused mappings into a global list instead of unmapping them
> right away and add acpi_ev_system_release_memory_mappings() to
> be called when leaving the interpreter in order to unmap the
> unused memory mappings in the global list (which is protected
> by the namespace mutex).
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> drivers/acpi/acpica/acevents.h | 2 ++
> drivers/acpi/acpica/dbtest.c | 3 ++
> drivers/acpi/acpica/evrgnini.c | 51
> ++++++++++++++++++++++++++++++++--
> drivers/acpi/acpica/exutils.c | 3 ++
> drivers/acpi/acpica/utxface.c | 23 +++++++++++++++
> include/acpi/acpixf.h | 1 +
> 6 files changed, 80 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/acpi/acpica/acevents.h b/drivers/acpi/acpica/acevents.h
> index 79f292687bd6..463eb9124765 100644
> --- a/drivers/acpi/acpica/acevents.h
> +++ b/drivers/acpi/acpica/acevents.h
> @@ -197,6 +197,8 @@ acpi_ev_execute_reg_method(union
> acpi_operand_object *region_obj, u32 function);
> /*
> * evregini - Region initialization and setup
> */
> +void acpi_ev_system_release_memory_mappings(void);
> +
> acpi_status
> acpi_ev_system_memory_region_setup(acpi_handle handle,
> u32 function,
> diff --git a/drivers/acpi/acpica/dbtest.c b/drivers/acpi/acpica/dbtest.c
> index 6db44a5ac786..7dac6dae5c48 100644
> --- a/drivers/acpi/acpica/dbtest.c
> +++ b/drivers/acpi/acpica/dbtest.c
> @@ -8,6 +8,7 @@
> #include <acpi/acpi.h>
> #include "accommon.h"
> #include "acdebug.h"
> +#include "acevents.h"
> #include "acnamesp.h"
> #include "acpredef.h"
> #include "acinterp.h"
> @@ -768,6 +769,8 @@ acpi_db_test_field_unit_type(union
> acpi_operand_object *obj_desc)
> acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
> acpi_ut_release_mutex(ACPI_MTX_INTERPRETER);
>
> + acpi_ev_system_release_memory_mappings();
> +
> bit_length = obj_desc->common_field.bit_length;
> byte_length =
> ACPI_ROUND_BITS_UP_TO_BYTES(bit_length);
>
> diff --git a/drivers/acpi/acpica/evrgnini.c b/drivers/acpi/acpica/evrgnini.c
> index 48a5e6eaf9b9..946c4eef054d 100644
> --- a/drivers/acpi/acpica/evrgnini.c
> +++ b/drivers/acpi/acpica/evrgnini.c
> @@ -16,6 +16,52 @@
> #define _COMPONENT ACPI_EVENTS
> ACPI_MODULE_NAME("evrgnini")
>
> +#ifdef ACPI_OS_MAP_MEMORY_FAST_PATH
> +static struct acpi_mem_mapping *unused_memory_mappings;
> +
> +/*********************************************************
> **********************
> + *
> + * FUNCTION: acpi_ev_system_release_memory_mappings
> + *
> + * PARAMETERS: None
> + *
> + * RETURN: None
> + *
> + * DESCRIPTION: Release all of the unused memory mappings in the queue
> + * under the interpreter mutex.
> + *
> +
> **********************************************************
> ********************/
> +void acpi_ev_system_release_memory_mappings(void)
> +{
> + struct acpi_mem_mapping *mapping;
> +
> +
> ACPI_FUNCTION_TRACE(acpi_ev_system_release_memory_mappin
> gs);
> +
> + acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);
> +
> + while (unused_memory_mappings) {
> + mapping = unused_memory_mappings;
> + unused_memory_mappings = mapping->next;
> +
> + acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
> +
> + acpi_os_unmap_memory(mapping->logical_address,
> mapping->length);
acpi_os_unmap_memory calls synchronize_rcu_expedited(). I'm no RCU expert but the
definition of this function states:
* Although this is a great improvement over previous expedited
* implementations, it is still unfriendly to real-time workloads, so is
* thus not recommended for any sort of common-case code. In fact, if
* you are using synchronize_rcu_expedited() in a loop, please restructure
* your code to batch your updates, and then use a single synchronize_rcu()
* instead.
> + ACPI_FREE(mapping);
> +
> + acpi_ut_acquire_mutex(ACPI_MTX_NAMESPACE);
> + }
> +
> + acpi_ut_release_mutex(ACPI_MTX_NAMESPACE);
> +
> + return_VOID;
> +}
> +#else /* !ACPI_OS_MAP_MEMORY_FAST_PATH */
> +void acpi_ev_system_release_memory_mappings(void)
> +{
> + return_VOID;
> +}
> +#endif /* !ACPI_OS_MAP_MEMORY_FAST_PATH */
> +
>
> /**********************************************************
> *********************
> *
> * FUNCTION: acpi_ev_system_memory_region_setup
> @@ -60,9 +106,8 @@ acpi_ev_system_memory_region_setup(acpi_handle
> handle,
> while (local_region_context->first_mapping)
> {
> mapping = local_region_context-
> >first_mapping;
> local_region_context->first_mapping
> = mapping->next;
> - acpi_os_unmap_memory(mapping-
> >logical_address,
> - mapping->length);
> - ACPI_FREE(mapping);
> + mapping->next =
> unused_memory_mappings;
> + unused_memory_mappings =
> mapping;
> }
> #endif
> }
> diff --git a/drivers/acpi/acpica/exutils.c b/drivers/acpi/acpica/exutils.c
> index 8fefa6feac2f..516d67664392 100644
> --- a/drivers/acpi/acpica/exutils.c
> +++ b/drivers/acpi/acpica/exutils.c
> @@ -25,6 +25,7 @@
>
> #include <acpi/acpi.h>
> #include "accommon.h"
> +#include "acevents.h"
> #include "acinterp.h"
> #include "amlcode.h"
>
> @@ -106,6 +107,8 @@ void acpi_ex_exit_interpreter(void)
> "Could not release AML Interpreter mutex"));
> }
>
> + acpi_ev_system_release_memory_mappings();
> +
> return_VOID;
> }
>
> diff --git a/drivers/acpi/acpica/utxface.c b/drivers/acpi/acpica/utxface.c
> index ca7c9f0144ef..d972696be846 100644
> --- a/drivers/acpi/acpica/utxface.c
> +++ b/drivers/acpi/acpica/utxface.c
> @@ -11,6 +11,7 @@
>
> #include <acpi/acpi.h>
> #include "accommon.h"
> +#include "acevents.h"
> #include "acdebug.h"
>
> #define _COMPONENT ACPI_UTILITIES
> @@ -244,6 +245,28 @@ acpi_status acpi_purge_cached_objects(void)
>
> ACPI_EXPORT_SYMBOL(acpi_purge_cached_objects)
>
> +/*********************************************************
> ********************
> + *
> + * FUNCTION: acpi_release_unused_memory_mappings
> + *
> + * PARAMETERS: None
> + *
> + * RETURN: None
> + *
> + * DESCRIPTION: Remove memory mappings that are not used any more.
> + *
> +
> **********************************************************
> ******************/
> +void acpi_release_unused_memory_mappings(void)
> +{
> + ACPI_FUNCTION_TRACE(acpi_release_unused_memory_mappings);
> +
> + acpi_ev_system_release_memory_mappings();
> +
> + return_VOID;
> +}
> +
> +ACPI_EXPORT_SYMBOL(acpi_release_unused_memory_mappings)
> +
>
> /**********************************************************
> *******************
> *
> * FUNCTION: acpi_install_interface
> diff --git a/include/acpi/acpixf.h b/include/acpi/acpixf.h
> index 1dc8d262035b..8d2cc02257ed 100644
> --- a/include/acpi/acpixf.h
> +++ b/include/acpi/acpixf.h
> @@ -449,6 +449,7 @@ ACPI_EXTERNAL_RETURN_STATUS(acpi_status
> acpi_size length,
> struct acpi_pld_info
> **return_buffer))
> +ACPI_EXTERNAL_RETURN_VOID(void
> acpi_release_unused_memory_mappings(void))
>
> /*
> * ACPI table load/unload interfaces
> --
> 2.26.2
>
>
>
