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Date:   Fri, 12 Jun 2020 00:12:05 +0000
From:   "Kaneda, Erik" <erik.kaneda@...el.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Williams, Dan J" <dan.j.williams@...el.com>
CC:     "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        James Morse <james.morse@....com>,
        Myron Stowe <myron.stowe@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "Moore, Robert" <robert.moore@...el.com>
Subject: RE: [RFT][PATCH 2/3] ACPICA: Remove unused memory mappings on
 interpreter exit



> -----Original Message-----
> From: Rafael J. Wysocki <rjw@...ysocki.net>
> Sent: Wednesday, June 10, 2020 5:22 AM
> To: Williams, Dan J <dan.j.williams@...el.com>
> Cc: Kaneda, Erik <erik.kaneda@...el.com>; Wysocki, Rafael J
> <rafael.j.wysocki@...el.com>; Len Brown <lenb@...nel.org>; Borislav
> Petkov <bp@...en8.de>; Weiny, Ira <ira.weiny@...el.com>; James Morse
> <james.morse@....com>; Myron Stowe <myron.stowe@...hat.com>;
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com>; linux-
> kernel@...r.kernel.org; linux-acpi@...r.kernel.org; linux-
> nvdimm@...ts.01.org; Moore, Robert <robert.moore@...el.com>
> Subject: [RFT][PATCH 2/3] ACPICA: Remove unused memory mappings on
> interpreter exit
> 
> From: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> 
> 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@...el.com>
> ---
>  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
> 
> 
> 

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