source: trunk/kernel/mm/kcm.c

/*
 * kcm.c -  Kernel Cache Manager implementation.
 *
 * Author  Alain Greiner    (2016,2017,2018,2019,2020)
 *
 * Copyright (c) UPMC Sorbonne Universites
 *
 * This file is part of ALMOS-MKH.
 *
 * ALMOS-MKH is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2.0 of the License.
 *
 * ALMOS-MKH is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ALMOS-MKH; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <kernel_config.h>
#include <hal_kernel_types.h>
#include <hal_special.h>
#include <busylock.h>
#include <list.h>
#include <printk.h>
#include <bits.h>
#include <ppm.h>
#include <thread.h>
#include <page.h>
#include <cluster.h>
#include <kmem.h>
#include <kcm.h>

///////////////////////////////////////////////////////////////////////////////////////////
//         global variables
///////////////////////////////////////////////////////////////////////////////////////////

extern chdev_directory_t    chdev_dir;          // allocated in kernel_init.c


/////////////////////////////////////////////////////////////////////////////////////
//        Local access functions
/////////////////////////////////////////////////////////////////////////////////////

//////////////////////////////////////////////////////////////////////////////////////
// This static function is called by the kcm_alloc() function.
// It returns a pointer on a block allocated from an active kcm_page.
// It makes a panic if no block is available in the selected page.
// It changes the page status as required.
//////////////////////////////////////////////////////////////////////////////////////
// @ kcm      : pointer on KCM allocator.
// @ kcm_page : pointer on an active kcm_page.
// @ return pointer on allocated block.
/////////////////////////////////////////////////////////////////////////////////////
static void * __attribute__((noinline)) kcm_get_block( kcm_t      * kcm,
                                                       kcm_page_t * kcm_page )
{
    // initialise variables
    uint32_t order  = kcm->order;
    uint32_t count  = kcm_page->count;
    uint64_t status = kcm_page->status;

// check kcm page not full
assert( __FUNCTION__, (count < 63) ,
"kcm_page should not be full / cxy %x / order %d / count %d", local_cxy, order, count );

    uint32_t index  = 1;
    uint64_t mask   = (uint64_t)0x2;

        // allocate first free block in kcm_page, update status,
    // and count , compute index of allocated block in kcm_page 
    while( index <= 63 )
    {
        if( (status & mask) == 0 )   // block found
        {
            // update page count and status
            kcm_page->status = status | mask;
            kcm_page->count  = count + 1;
            break;      
        }
        
        index++;
        mask <<= 1;
    }

    // switch page to full if last block
    if( (count + 1) == 63 )
    {
                list_unlink( &kcm_page->list);
                kcm->active_pages_nr--;

        list_add_first( &kcm->full_root , &kcm_page->list );
                kcm->full_pages_nr ++;
    }

        // compute return pointer
        void * ptr = (void *)((intptr_t)kcm_page + (index << order));

        return ptr;

}  // end kcm_get_block()

/////////////////////////////////////////////////////////////////////////////////////
// This static function is called by the kcm_free() function.
// It releases a previously allocated block to the relevant kcm_page.
// It makes a panic if the released block is not allocated in this page.
// It changes the kcm_page status as required.
/////////////////////////////////////////////////////////////////////////////////////
// @ kcm        : pointer on kcm allocator.
// @ kcm_page   : pointer on kcm_page.
// @ block_ptr  : pointer on block to be released.
/////////////////////////////////////////////////////////////////////////////////////
static void __attribute__((noinline)) kcm_put_block ( kcm_t      * kcm,
                                                      kcm_page_t * kcm_page,
                                                      void       * block_ptr )
{
    // initialise variables
    uint32_t order  = kcm->order;
    uint32_t count  = kcm_page->count;
    uint64_t status = kcm_page->status;
    
        // compute block index from block pointer and kcm_page pointer
        uint32_t index = ((intptr_t)block_ptr - (intptr_t)kcm_page) >> order;

    // compute mask in bit vector
    uint64_t mask = ((uint64_t)0x1) << index;

    if( (status & mask) == 0 )
    {
        printk("\n[WARNING] in %s : block[%x,%x] not allocated / kcm %x / kcm_page %x\n",
        __FUNCTION__, local_cxy, block_ptr, kcm, kcm_page );
        kcm_remote_display( local_cxy , kcm );
        return;
    }

    // update status & count in kcm_page 
        kcm_page->status = status & ~mask;
        kcm_page->count  = count - 1;

        // switch page to active if it was full
        if( count == 63 )
        {
                list_unlink( &kcm_page->list );
                kcm->full_pages_nr --;

                list_add_last( &kcm->active_root, &kcm_page->list );
                kcm->active_pages_nr ++;
        }

}  // kcm_put_block()

/////////////////////////////////////////////////////////////////////////////////////
// This static function  returns one non-full kcm_page with the following policy :
// - if the "active_list" is non empty, it returns the first "active" page,
//   without modifying the KCM state.
// - if the "active_list" is empty, it allocates a new page from PPM, inserts
//   this page in the active_list, and returns it. 
/////////////////////////////////////////////////////////////////////////////////////
// @ kcm      : local pointer on local KCM allocator.
// @ return pointer on a non-full kcm page if success / returns NULL if no memory.
/////////////////////////////////////////////////////////////////////////////////////
static kcm_page_t * __attribute__((noinline)) kcm_get_page( kcm_t * kcm )
{
    kcm_page_t * kcm_page;

    uint32_t active_pages_nr = kcm->active_pages_nr;

    if( active_pages_nr > 0 )       // return first active page
    {
        kcm_page = LIST_FIRST( &kcm->active_root , kcm_page_t , list );
    }
    else                            // allocate a new page from PPM
        {
        // get KCM order
        uint32_t order = kcm->order;

        // get one kcm_page from  PPM
        page_t * page = ppm_alloc_pages( order + 6 - CONFIG_PPM_PAGE_ORDER );

            if( page == NULL )
            {

#if DEBUG_KCM_ERROR
printk("\n[ERROR] in %s : failed to allocate page in cluster %x\n",
__FUNCTION__ , local_cxy );
#endif
                    return NULL;
        }

            // get page base address
            xptr_t base_xp = ppm_page2base( XPTR( local_cxy , page ) );

        // get local pointer on kcm_page 
            kcm_page = GET_PTR( base_xp );

            // initialize kcm_page descriptor
            kcm_page->status = 0;
            kcm_page->count  = 0;
            kcm_page->kcm    = kcm;
            kcm_page->page   = page;

            // introduce new page in KCM active_list
            list_add_first( &kcm->active_root , &kcm_page->list );
            kcm->active_pages_nr ++;
        }

        return kcm_page;

}  // end kcm_get_page()

//////////////////////////////
void kcm_init( kcm_t    * kcm,
                   uint32_t   order)
{

// check argument
assert( __FUNCTION__, (order < CONFIG_PPM_PAGE_ORDER),
"order argument %d too large", order );

assert( __FUNCTION__, (order >= CONFIG_CACHE_LINE_ORDER),
"order argument %d too small", order );

        // initialize lock
        remote_busylock_init( XPTR( local_cxy , &kcm->lock ) , LOCK_KCM_STATE );

        // initialize KCM page lists
        kcm->full_pages_nr   = 0;
        kcm->active_pages_nr = 0;
        list_root_init( &kcm->full_root );
        list_root_init( &kcm->active_root );

        // initialize order 
        kcm->order = order;
 
#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) )
printk("\n[%s] cxy %x / order %d\n",
__FUNCTION__, local_cxy, order );
#endif

}  // end kcm_init()

///////////////////////////////
void kcm_destroy( kcm_t * kcm )
{
        kcm_page_t   * kcm_page;

    // build extended pointer on  KCM lock
    xptr_t lock_xp = XPTR( local_cxy , &kcm->lock );

        // get KCM lock
        remote_busylock_acquire( lock_xp );

        // release all full pages
        while( list_is_empty( &kcm->full_root ) == false )
        {
                kcm_page = LIST_FIRST( &kcm->full_root , kcm_page_t , list );
                list_unlink( &kcm_page->list );
                ppm_free_pages( kcm_page->page );
        }

    // release all empty pages
    while( list_is_empty( &kcm->active_root ) == false )
        {
                kcm_page = LIST_FIRST( &kcm->active_root , kcm_page_t , list );
                list_unlink( &kcm_page->list );
                ppm_free_pages( kcm_page->page );
        }

        // release KCM lock
        remote_busylock_release( lock_xp );

}  // end kcm_destroy()

//////////////////////////////////
void * kcm_alloc( uint32_t order )
{
    kcm_t      * kcm;
        kcm_page_t * kcm_page;
        void       * block;

// check argument
assert( __FUNCTION__, (order < CONFIG_PPM_PAGE_ORDER),
"order argument %d too large", order );

#if DEBUG_KCM
uint32_t cycle = (uint32_t)hal_get_cycles();
#endif

    // smallest block size is a cache line
    if (order < CONFIG_CACHE_LINE_ORDER) order = CONFIG_CACHE_LINE_ORDER;

    // get local pointer on relevant KCM allocator
    kcm = &LOCAL_CLUSTER->kcm[order - CONFIG_CACHE_LINE_ORDER];

    // build extended pointer on local KCM lock
    xptr_t lock_xp = XPTR( local_cxy , &kcm->lock );

        // get KCM lock
        remote_busylock_acquire( lock_xp );

    // get a non-full kcm_page
    kcm_page = kcm_get_page( kcm );

    if( kcm_page == NULL )
        {
                remote_busylock_release( lock_xp );
                return NULL;
        }

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] enter / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, local_cxy, kcm, kcm->full_pages_nr, kcm->active_pages_nr,
kcm_page, (uint32_t)(kcm_page->status>>32), (uint32_t)(kcm_page->status), kcm_page->count );
#endif

        // allocate a block from selected active page
        block = kcm_get_block( kcm , kcm_page );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] exit  / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, local_cxy, kcm, kcm->full_pages_nr, kcm->active_pages_nr,
kcm_page, (uint32_t)(kcm_page->status>>32), (uint32_t)(kcm_page->status), kcm_page->count );
#endif

        // release lock
        remote_busylock_release( lock_xp );

        return block;

}  // end kcm_alloc()

///////////////////////////////
void kcm_free( void    * block,
               uint32_t  order )
{
    kcm_t      * kcm;
        kcm_page_t * kcm_page;

// check argument
assert( __FUNCTION__, (block != NULL), 
"block pointer cannot be NULL" );

#if DEBUG_KCM
uint32_t cycle = (uint32_t)hal_get_cycles();
#endif

    // smallest block size is a cache line
    if (order < CONFIG_CACHE_LINE_ORDER) order = CONFIG_CACHE_LINE_ORDER;

    // get local pointer on relevant KCM allocator
    kcm = &LOCAL_CLUSTER->kcm[order - CONFIG_CACHE_LINE_ORDER];

    // get local pointer on KCM page
    intptr_t kcm_page_mask = (1 << (order + 6)) - 1; 
        kcm_page = (kcm_page_t *)((intptr_t)block & ~kcm_page_mask);

    // build extended pointer on local KCM lock
    xptr_t lock_xp = XPTR( local_cxy , &kcm->lock );

        // get lock
        remote_busylock_acquire( lock_xp );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] exit  / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, local_cxy, kcm, kcm->full_pages_nr, kcm->active_pages_nr,
kcm_page, (uint32_t)(kcm_page->status>>32), (uint32_t)(kcm_page->status), kcm_page->count );
#endif

        // release the block to the relevant page
        kcm_put_block( kcm , kcm_page , block );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] exit  / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, local_cxy, kcm, kcm->full_pages_nr, kcm->active_pages_nr,
kcm_page, (uint32_t)(kcm_page->status>>32), (uint32_t)(kcm_page->status), kcm_page->count );
#endif

        // release lock
        remote_busylock_release( lock_xp );

}  // end kcm_free() 


/////////////////////////////////////////////////////////////////////////////////////
//        Remote access functions
/////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////////////////////
// This static function is called by the kcm_remote_alloc() function.
// It can be called by any thread running in any cluster.
// It returns a local pointer on a block allocated from an active kcm_page.
// It makes a panic if no block available in the selected kcm_page.
// It changes the page status as required.
/////////////////////////////////////////////////////////////////////////////////////
// @ kcm_cxy  : remote KCM cluster identifier.
// @ kcm_ptr  : local pointer on remote KCM allocator.
// @ kcm_page : local pointer on remote active kcm_page to use.
// @ return a local pointer on the allocated block. 
/////////////////////////////////////////////////////////////////////////////////////
static void * __attribute__((noinline)) kcm_remote_get_block( cxy_t        kcm_cxy,
                                                              kcm_t      * kcm_ptr,
                                                              kcm_page_t * kcm_page )
{
    uint32_t order  = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->order ) );
    uint32_t count  = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ) );
    uint64_t status = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ) );

// check kcm_page not full
assert( __FUNCTION__, (count < 63) , 
"kcm_page should not be full / cxy %x / order %d / count %d", kcm_cxy, order, count );

    uint32_t index  = 1;
    uint64_t mask   = (uint64_t)0x2;
    
        // allocate first free block in kcm_page, update status,
    // and count , compute index of allocated block in kcm_page 
    while( index <= 63 )
    {
        if( (status & mask) == 0 )   // block found
        {
            hal_remote_s64( XPTR( kcm_cxy , &kcm_page->status ) , status | mask );
            hal_remote_s32( XPTR( kcm_cxy , &kcm_page->count  ) , count + 1 );
            break;      
        }
        
        index++;
        mask <<= 1;
    }

        // swich the page to full if last block
        if( (count + 1) == 63 )
        {
                list_remote_unlink( kcm_cxy , &kcm_page->list );
                hal_remote_atomic_add( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ) , -1 );

                list_remote_add_first( kcm_cxy , &kcm_ptr->full_root , &kcm_page->list );
                hal_remote_atomic_add( XPTR( kcm_cxy , &kcm_ptr->full_pages_nr ) , 1 );
        }

        // compute return pointer
        void * ptr = (void *)((intptr_t)kcm_page + (index << order));

        return ptr;

}  // end kcm_remote_get_block()

/////////////////////////////////////////////////////////////////////////////////////
// This static function is called by the kcm_remote_free() function.
// It can be called by any thread running in any cluster.
// It releases a previously allocated block to the relevant kcm_page.
// It changes the kcm_page status as required.
/////////////////////////////////////////////////////////////////////////////////////
// @ kcm_cxy   : remote KCM cluster identifier
// @ kcm_ptr   : local pointer on remote KCM.
// @ kcm_page  : local pointer on kcm_page.
// @ block_ptr : pointer on block to be released.
/////////////////////////////////////////////////////////////////////////////////////
static void __attribute__((noinline)) kcm_remote_put_block ( cxy_t        kcm_cxy,
                                                             kcm_t      * kcm_ptr,
                                                             kcm_page_t * kcm_page,
                                                             void       * block_ptr )
{
    uint32_t order  = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->order ) );
    uint32_t count  = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ) );
    uint64_t status = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ) );
    
        // compute block index from block pointer and kcm_page pointer
        uint32_t index = ((intptr_t)block_ptr - (intptr_t)kcm_page) >> order;

    // compute mask in bit vector
    uint64_t mask = ((uint64_t)0x1) << index;

    if( (status & mask) == 0 )
    {
        printk("\n[WARNING] in %s : block[%x,%x] not allocated / kcm %x / kcm_page %x\n",
        __FUNCTION__, kcm_cxy, block_ptr, kcm_ptr, kcm_page );
        kcm_remote_display( kcm_cxy , kcm_ptr );
        return;
    }

    // update status & count in kcm_page 
        hal_remote_s64( XPTR( kcm_cxy , &kcm_page->status ) , status & ~mask );
        hal_remote_s32( XPTR( kcm_cxy , &kcm_page->count  ) , count - 1 );

        // switch the page to active if page was full
        if( count == 63 )
        {
                list_remote_unlink( kcm_cxy , &kcm_page->list );
                hal_remote_atomic_add( XPTR( kcm_cxy , &kcm_ptr->full_pages_nr ) , -1 );

                list_remote_add_last( kcm_cxy , &kcm_ptr->active_root, &kcm_page->list );
                hal_remote_atomic_add( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ) , 1 );
        }

}  // end kcm_remote_put_block()

/////////////////////////////////////////////////////////////////////////////////////
// This static function can be called by any thread running in any cluster.
// It gets one non-full KCM page from the remote KCM.
// It allocates a page from remote PPM to populate the freelist, and initialises
// the kcm_page descriptor when required.
/////////////////////////////////////////////////////////////////////////////////////
static kcm_page_t * __attribute__((noinline)) kcm_remote_get_page( cxy_t    kcm_cxy,
                                                                   kcm_t  * kcm_ptr )
{
    kcm_page_t * kcm_page;    // local pointer on remote KCM page 

    uint32_t active_pages_nr = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ) );

    if( active_pages_nr > 0 )       // return first active page
    {
        kcm_page = LIST_REMOTE_FIRST( kcm_cxy , &kcm_ptr->active_root , kcm_page_t , list );
    }
    else                            // allocate a new page from PPM
        {
        // get KCM order
        uint32_t order = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->order ));

        // get one kcm_page from PPM
        xptr_t page_xp = ppm_remote_alloc_pages( kcm_cxy,
                                                 order + 6 - CONFIG_PPM_PAGE_ORDER );
            if( page_xp == XPTR_NULL )
            {

#if DEBUG_KCM_ERROR
printk("\n[ERROR] in %s : failed to allocate page in cluster %x\n",
__FUNCTION__ , kcm_cxy );
#endif
                    return NULL;
        }

            // get extended pointer on allocated buffer
            xptr_t base_xp = ppm_page2base( page_xp );

        // get local pointer on kcm_page
            kcm_page = GET_PTR( base_xp );

            // initialize kcm_page descriptor
            hal_remote_s32( XPTR( kcm_cxy , &kcm_page->count )  , 0 );
            hal_remote_s64( XPTR( kcm_cxy , &kcm_page->status ) , 0 );
            hal_remote_spt( XPTR( kcm_cxy , &kcm_page->kcm )    , kcm_ptr );
            hal_remote_spt( XPTR( kcm_cxy , &kcm_page->page )   , GET_PTR( page_xp ) );

            // introduce new page in remote KCM active_list
            list_remote_add_first( kcm_cxy , &kcm_ptr->active_root , &kcm_page->list );
            hal_remote_atomic_add( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ) , 1 );
        }

        return kcm_page;

}  // end kcm_remote_get_page()

//////////////////////////////////////////
void * kcm_remote_alloc( cxy_t    kcm_cxy,
                         uint32_t order )
{
    kcm_t      * kcm_ptr;
    kcm_page_t * kcm_page;
    void       * block_ptr;

// check kcm_cxy argument
assert( __FUNCTION__, cluster_is_active( kcm_cxy ),
"cluster %x not active", kcm_cxy );

// check order argument
assert( __FUNCTION__, (order < CONFIG_PPM_PAGE_ORDER) ,
"order argument %d too large", order );

    // smallest size is a cache line
    if( order < CONFIG_CACHE_LINE_ORDER ) order = CONFIG_CACHE_LINE_ORDER;

    // get local pointer on relevant KCM allocator (same in all clusters)
    kcm_ptr = &LOCAL_CLUSTER->kcm[order - 6];

    // build extended pointer on remote KCM lock
    xptr_t lock_xp = XPTR( kcm_cxy , &kcm_ptr->lock );

        // get lock
        remote_busylock_acquire( lock_xp );

    // get a non-full kcm_page
    kcm_page = kcm_remote_get_page( kcm_cxy , kcm_ptr );

    if( kcm_page == NULL )
        {
                remote_busylock_release( lock_xp );
                return NULL;
        }

#if DEBUG_KCM
uint32_t cycle     = (uint32_t)hal_get_cycles();
uint32_t nb_full   = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->full_pages_nr ));
uint32_t nb_active = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ));
uint64_t status    = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ));
uint32_t count     = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ));
#endif


#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] enter / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, kcm_cxy, kcm_ptr, nb_full, nb_active,
kcm_page, (uint32_t)(status>>32), (uint32_t)(status), kcm_page->count );
#endif

        // get a block from selected active page
        block_ptr = kcm_remote_get_block( kcm_cxy , kcm_ptr , kcm_page );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] exit  / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, kcm_cxy, kcm_ptr, nb_full, nb_active,
kcm_page, (uint32_t)(status>>32), (uint32_t)(status), kcm_page->count );
#endif

        // release lock
        remote_busylock_release( lock_xp );

        return block_ptr;

}  // end kcm_remote_alloc()

////////////////////////////////////////
void kcm_remote_free( cxy_t     kcm_cxy,
                      void    * block_ptr,
                      uint32_t  order )
{
        kcm_t      * kcm_ptr;
        kcm_page_t * kcm_page;

// check kcm_cxy argument
assert( __FUNCTION__, cluster_is_active( kcm_cxy ),
"cluster %x not active", kcm_cxy );

// check block_ptr argument
assert( __FUNCTION__, (block_ptr != NULL),
"block pointer cannot be NULL" );

// check order argument
assert( __FUNCTION__, (order < CONFIG_PPM_PAGE_ORDER) ,
"order argument %d too large", order );

    // smallest block size is a cache line
    if (order < CONFIG_CACHE_LINE_ORDER) order = CONFIG_CACHE_LINE_ORDER;

    // get local pointer on relevant KCM allocator (same in all clusters)
    kcm_ptr = &LOCAL_CLUSTER->kcm[order - CONFIG_CACHE_LINE_ORDER];

    // get local pointer on KCM page
    intptr_t kcm_page_mask = (1 << (order + 6)) - 1; 
        kcm_page = (kcm_page_t *)((intptr_t)block_ptr & ~kcm_page_mask);

#if DEBUG_KCM
uint32_t cycle     = (uint32_t)hal_get_cycles();
uint32_t nb_full   = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->full_pages_nr ));
uint32_t nb_active = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ));
uint64_t status    = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ));
uint32_t count     = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ));
#endif

    // build extended pointer on remote KCM lock
    xptr_t lock_xp = XPTR( kcm_cxy , &kcm_ptr->lock );

        // get lock
        remote_busylock_acquire( lock_xp );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] enter / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, kcm_cxy, kcm_ptr, nb_full, nb_active,
kcm_page, (uint32_t)(status>>32), (uint32_t)(status), kcm_page->count );
#endif

        // release the block to the relevant page
        kcm_remote_put_block( kcm_cxy , kcm_ptr , kcm_page , block_ptr );

#if DEBUG_KCM
if( (DEBUG_KCM_ORDER == order) && (DEBUG_KCM_CXY == local_cxy) && (DEBUG_KCM < cycle) )
printk("\n[%s] exit  / order %d / kcm[%x,%x] / nb_full %d / nb_active %d\n"
"    page %x / status [%x,%x] / count %d\n",
__FUNCTION__, order, kcm_cxy, kcm_ptr, nb_full, nb_active,
kcm_page, (uint32_t)(status>>32), (uint32_t)(status), kcm_page->count );
#endif

        // release lock
        remote_busylock_release( lock_xp );

}  // end kcm_remote_free

/////////////////////////////////////////
void kcm_remote_display( cxy_t   kcm_cxy,
                         kcm_t * kcm_ptr )
{
    list_entry_t * iter;
    kcm_page_t   * kcm_page;
    uint64_t       status;
    uint32_t       count;

    // get pointers on TXT0 chdev
    xptr_t    txt0_xp  = chdev_dir.txt_tx[0];
    cxy_t     txt0_cxy = GET_CXY( txt0_xp );
    chdev_t * txt0_ptr = GET_PTR( txt0_xp );

    // get extended pointer on remote TXT0 chdev lock
    xptr_t    txt0_lock_xp = XPTR( txt0_cxy , &txt0_ptr->wait_lock );

    // get TXT0 lock 
    remote_busylock_acquire( txt0_lock_xp );

    uint32_t order           = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->order) );
    uint32_t full_pages_nr   = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->full_pages_nr ) );
    uint32_t active_pages_nr = hal_remote_l32( XPTR( kcm_cxy , &kcm_ptr->active_pages_nr ) );

        nolock_printk("*** KCM : cxy %x / order %d / full_pages_nr %d / active_pages_nr %d\n",
        kcm_cxy, order, full_pages_nr, active_pages_nr );

    if( active_pages_nr )
    {
        LIST_REMOTE_FOREACH( kcm_cxy , &kcm_ptr->active_root , iter )
        {
            kcm_page = LIST_ELEMENT( iter , kcm_page_t , list );
            status   = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ) );
            count    = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ) );

            nolock_printk("- active page %x / status (%x,%x) / count %d\n",
            kcm_page, (uint32_t)( status<< 32 ), (uint32_t)( status ), count );
        }
    }

    if( full_pages_nr )
    {
        LIST_REMOTE_FOREACH( kcm_cxy , &kcm_ptr->full_root , iter )
        {
            kcm_page = LIST_ELEMENT( iter , kcm_page_t , list );
            status   = hal_remote_l64( XPTR( kcm_cxy , &kcm_page->status ) );
            count    = hal_remote_l32( XPTR( kcm_cxy , &kcm_page->count ) );

            nolock_printk("- full page %x / status (%x,%x) / count %d\n",
            kcm_page, (uint32_t)( status<< 32 ), (uint32_t)( status ), count );
        }
    }

    // release TXT0 lock 
    remote_busylock_release( txt0_lock_xp );

}  // end kcm remote_display()