[PATCH 2/2] malloc: Make deferred free support optional

[Gedare Bloom]

looks good, other than my comment on 1/2.

On Thu, Jul 23, 2020 at 6:21 AM Sebastian Huber
<sebastian.huber at embedded-brains.de> wrote:
>
> Only include the deferred free support if free() is actually used by the
> application.
>
> The free() implementation in RTEMS supports that allocated memory is
> freed in interrupt context.  Since the heap is protected by a mutex, the
> frees issued in interrupt context cannot immediately be freed to the
> heap, instead they are placed on a deferred free list.  This list is
> emptied by the core allocation function
> rtems_heap_allocate_aligned_with_boundary().  This adds a dependency to
> free() in rtems_heap_allocate_aligned_with_boundary(). In order to
> better support applications which only allocate memory and never free
> it, this dependency should be avoided.  Provide a weak default
> implementation of _Malloc_Process_deferred_frees() for
> rtems_heap_allocate_aligned_with_boundary().  In the free() module
> provide the strong implementation.
>
> Update #4032.
> ---
>  cpukit/libcsupport/src/free.c            | 43 ++++++++++++++++++++++++
>  cpukit/libcsupport/src/malloc_deferred.c | 40 ++--------------------
>  cpukit/libcsupport/src/malloc_p.h        |  2 --
>  3 files changed, 46 insertions(+), 39 deletions(-)
>
> diff --git a/cpukit/libcsupport/src/free.c b/cpukit/libcsupport/src/free.c
> index f4542e0c72..9f7c577852 100644
> --- a/cpukit/libcsupport/src/free.c
> +++ b/cpukit/libcsupport/src/free.c
> @@ -23,6 +23,49 @@
>  #include "malloc_p.h"
>  #include <stdlib.h>
>
> +#include <rtems/chain.h>
> +
> +static RTEMS_CHAIN_DEFINE_EMPTY( _Malloc_GC_list );
> +
> +RTEMS_INTERRUPT_LOCK_DEFINE( static, _Malloc_GC_lock, "Malloc GC" )
> +
> +static void *_Malloc_Get_deferred_free( void )
> +{
> +  rtems_interrupt_lock_context lock_context;
> +  void *p;
> +
> +  rtems_interrupt_lock_acquire( &_Malloc_GC_lock, &lock_context );
> +  p = rtems_chain_get_unprotected( &_Malloc_GC_list );
> +  rtems_interrupt_lock_release( &_Malloc_GC_lock, &lock_context );
> +
> +  return p;
> +}
> +
> +void _Malloc_Process_deferred_frees( void )
> +{
> +  rtems_chain_node *to_be_freed;
> +
> +  /*
> +   *  If some free's have been deferred, then do them now.
> +   */
> +  while ( ( to_be_freed = _Malloc_Get_deferred_free() ) != NULL ) {
> +    free( to_be_freed );
> +  }
> +}
> +
> +static void _Malloc_Deferred_free( void *p )
> +{
> +  rtems_interrupt_lock_context lock_context;
> +  rtems_chain_node *node;
> +
> +  node = (rtems_chain_node *) p;
> +
> +  rtems_interrupt_lock_acquire( &_Malloc_GC_lock, &lock_context );
> +  rtems_chain_initialize_node( node );
> +  rtems_chain_append_unprotected( &_Malloc_GC_list, node );
> +  rtems_interrupt_lock_release( &_Malloc_GC_lock, &lock_context );
> +}
> +
>  void free(
>    void *ptr
>  )
> diff --git a/cpukit/libcsupport/src/malloc_deferred.c b/cpukit/libcsupport/src/malloc_deferred.c
> index 62c231d2f8..f66dd54676 100644
> --- a/cpukit/libcsupport/src/malloc_deferred.c
> +++ b/cpukit/libcsupport/src/malloc_deferred.c
> @@ -27,14 +27,9 @@
>
>  #include "malloc_p.h"
>
> -#include <rtems/chain.h>
>  #include <rtems/score/sysstate.h>
>  #include <rtems/score/threaddispatch.h>
>
> -static RTEMS_CHAIN_DEFINE_EMPTY( _Malloc_GC_list );
> -
> -RTEMS_INTERRUPT_LOCK_DEFINE( static, _Malloc_GC_lock, "Malloc GC" )
> -
>  Malloc_System_state _Malloc_System_state( void )
>  {
>    System_state_Codes state = _System_state_Get();
> @@ -52,28 +47,12 @@ Malloc_System_state _Malloc_System_state( void )
>    }
>  }
>
> -static void *_Malloc_Get_deferred_free( void )
> -{
> -  rtems_interrupt_lock_context lock_context;
> -  void *p;
> -
> -  rtems_interrupt_lock_acquire( &_Malloc_GC_lock, &lock_context );
> -  p = rtems_chain_get_unprotected( &_Malloc_GC_list );
> -  rtems_interrupt_lock_release( &_Malloc_GC_lock, &lock_context );
> -
> -  return p;
> -}
> -
> -void _Malloc_Process_deferred_frees( void )
> +RTEMS_WEAK void _Malloc_Process_deferred_frees( void )
>  {
> -  rtems_chain_node *to_be_freed;
> -
>    /*
> -   *  If some free's have been deferred, then do them now.
> +   * Do nothing by default.  If free() is used by the application, then a
> +   * strong implementation of this function will be provided.
>     */
> -  while ( ( to_be_freed = _Malloc_Get_deferred_free() ) != NULL ) {
> -    free( to_be_freed );
> -  }
>  }
>
>  void *rtems_heap_allocate_aligned_with_boundary(
> @@ -125,19 +104,6 @@ void *rtems_heap_allocate_aligned_with_boundary(
>    return p;
>  }
>
> -void _Malloc_Deferred_free( void *p )
> -{
> -  rtems_interrupt_lock_context lock_context;
> -  rtems_chain_node *node;
> -
> -  node = (rtems_chain_node *) p;
> -
> -  rtems_interrupt_lock_acquire( &_Malloc_GC_lock, &lock_context );
> -  rtems_chain_initialize_node( node );
> -  rtems_chain_append_unprotected( &_Malloc_GC_list, node );
> -  rtems_interrupt_lock_release( &_Malloc_GC_lock, &lock_context );
> -}
> -
>  void *rtems_malloc( size_t size )
>  {
>    if ( size == 0 ) {
> diff --git a/cpukit/libcsupport/src/malloc_p.h b/cpukit/libcsupport/src/malloc_p.h
> index f3715a9966..cb26050ff1 100644
> --- a/cpukit/libcsupport/src/malloc_p.h
> +++ b/cpukit/libcsupport/src/malloc_p.h
> @@ -25,8 +25,6 @@ typedef enum {
>
>  Malloc_System_state _Malloc_System_state( void );
>
> -void _Malloc_Deferred_free( void * );
> -
>  void _Malloc_Process_deferred_frees( void );
>
>  #ifdef __cplusplus
> --
> 2.26.2
>
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