xref: /docs/en/device-dev/kernel/kernel-small-debug-memory-info.md

# Memory Information Statistics


## Basic Concepts

Memory information includes the memory pool size, memory usage, remaining memory size, maximum free memory, memory waterline, number of memory nodes, and fragmentation rate.

- The memory waterline indicates the maximum memory used in a memory pool. The waterline value is updated each time the memory is allocated or released. The memory pool size can be optimized based on this value.

- The fragmentation rate indicates the fragmentation degree of the memory pool. If the fragmentation rate is high, there are a large number of free memory blocks in the memory pool but each block is small. You can use the following formula to calculate the fragmentation rate:<br>Fragmentation rate = 100 – 100 x Maximum free memory block size/Remaining memory size

- You can use **LOS_MemInfoGet()** to scan the node information in the memory pool and collect the related statistics.


## Function Configuration

**LOSCFG_MEM_WATERLINE** specifies the setting of the memory information statistics function. This function is disabled by default. If you want to obtain the memory waterline, enable it in **Debug-&gt; Enable MEM Debug-&gt; Enable memory pool waterline or not**.


## Development Guidelines


### How to Develop

Key structure:


```c
typedef struct {
    UINT32 totalUsedSize;       // Memory usage of the memory pool.
    UINT32 totalFreeSize;       // Remaining size of the memory pool.
    UINT32 maxFreeNodeSize;     // Maximum size of the free memory block in the memory pool.
    UINT32 usedNodeNum;         // Number of non-free memory blocks in the memory pool.
    UINT32 freeNodeNum;         // Number of free memory blocks in the memory pool.
#if (LOSCFG_MEM_WATERLINE == 1) // This function is disabled by default and can be enabled using the **menuconfig** tool.
    UINT32 usageWaterLine;      // Waterline of the memory pool.
#endif
} LOS_MEM_POOL_STATUS;
```

To obtain the memory waterline, call **LOS_MemInfoGet(VOID *pool, LOS_MEM_POOL_STATUS *poolStatus)**. The first parameter specifies the start address of the memory pool, and the second parameter specifies the handle of the **LOS_MEM_POOL_STATUS** type. The **usageWaterLine** field indicates the waterline.

To calculate the memory fragmentation rate, call **LOS_MemInfoGet** to obtain the remaining memory size and the maximum free memory block size in the memory pool, and then calculate the fragmentation rate of the dynamic memory pool as follows:

Fragmentation rate = 100 – 100 x Maximum free memory block size/Remaining memory size


### Development Example

This example implements the following:

1. Create a monitoring task to obtain information about the memory pool.

2. Call **LOS_MemInfoGet** to obtain the basic information about the memory pool.

3. Calculate the memory usage and fragmentation rate.

**Sample Code**

You can compile and verify the sample code in **kernel/liteos_a/testsuites/kernel/src/osTest.c**. The **MemTest()** function is called in **TestTaskEntry**.

The sample code is as follows:

```c
#include <stdio.h>
#include <string.h>
#include "los_task.h"
#include "los_memory.h"
#include "los_config.h"

void MemInfoTaskFunc(void)
{
    LOS_MEM_POOL_STATUS poolStatus = {0};

    /* pool is the memory address of the information to be collected. OS_SYS_MEM_ADDR is used as an example. */
    void *pool = OS_SYS_MEM_ADDR;
    LOS_MemInfoGet(pool, &poolStatus);
    /* Calculate the fragmentation rate of the memory pool. */
    unsigned char fragment = 100 - poolStatus.maxFreeNodeSize * 100 / poolStatus.totalFreeSize;
    /* Calculate the memory usage of the memory pool. */
    unsigned char usage = LOS_MemTotalUsedGet(pool) * 100 / LOS_MemPoolSizeGet(pool);
    dprintf("usage = %d, fragment = %d, maxFreeSize = %d, totalFreeSize = %d, waterLine = %d\n", usage, fragment,                            poolStatus.maxFreeNodeSize, poolStatus.totalFreeSize, poolStatus.usageWaterLine);
}

int MemTest(void)
{
    unsigned int ret;
    unsigned int taskID;
    TSK_INIT_PARAM_S taskStatus = {0};
    taskStatus.pfnTaskEntry = (TSK_ENTRY_FUNC)MemInfoTaskFunc;
    taskStatus.uwStackSize  = 0x1000;
    taskStatus.pcName       = "memInfo";
    taskStatus.usTaskPrio   = 10;
    ret = LOS_TaskCreate(&taskID, &taskStatus);
    if (ret != LOS_OK) {
        dprintf("task create failed\n");
        return LOS_NOK;
    }
    return LOS_OK;
}
```

**Verification**


The result is as follows:

The data may vary depending on the running environment.

```
usage = 22, fragment = 3, maxFreeSize = 49056, totalFreeSize = 50132, waterLine = 1414
```