源码分析: Memseg

概述

DPDK把连续的内存段称之为memseg，它的示意图如下：

数据结构

librte_eal/common/include/rte_memory.h

/**
 * Physical memory segment descriptor.
 */
 struct rte_memseg {
     phys_addr_t phys_addr;      /**< Start physical address. */
     union {
         void *addr;         /**< Start virtual address. */
         uint64_t addr_64;   /**< Makes sure addr is always 64 bits */
     };
 #ifdef RTE_LIBRTE_IVSHMEM
     phys_addr_t ioremap_addr; /**< Real physical address inside the VM */
 #endif
     size_t len;               /**< Length of the segment. */
     uint64_t hugepage_sz;     /**< The pagesize of underlying memory */
     int32_t socket_id;        /**< NUMA socket ID. */
     uint32_t nchannel;        /**< Number of channels. */
     uint32_t nrank;           /**< Number of ranks. */
 #ifdef RTE_LIBRTE_XEN_DOM0
     /**< store segment MFNs */
     uint64_t mfn[DOM0_NUM_MEMBLOCK];
 #endif
 } __rte_packed;

初始化

在rte_eal_hugepage_init(librte_eal/linuxapp/eal/eal_memory.c)中：

for (i = 0; i < nr_hugefiles; i++) {
    new_memseg = 0;

    /* if this is a new section, create a new memseg */
    if (i == 0)
        new_memseg = 1;
    else if (hugepage[i].socket_id != hugepage[i-1].socket_id)
        new_memseg = 1;
    else if (hugepage[i].size != hugepage[i-1].size)
        new_memseg = 1;
    else if ((hugepage[i].physaddr - hugepage[i-1].physaddr) !=
        hugepage[i].size)
        new_memseg = 1;
    else if (((unsigned long)hugepage[i].final_va -
        (unsigned long)hugepage[i-1].final_va) != hugepage[i].size)
        new_memseg = 1;

    if (new_memseg) {
        j += 1;
        if (j == RTE_MAX_MEMSEG)
            break;

        mcfg->memseg[j].phys_addr = hugepage[i].physaddr;
        mcfg->memseg[j].addr = hugepage[i].final_va;
        mcfg->memseg[j].len = hugepage[i].size;
        mcfg->memseg[j].socket_id = hugepage[i].socket_id;
        mcfg->memseg[j].hugepage_sz = hugepage[i].size;
    }
    /* continuation of previous memseg */
    else{
        mcfg->memseg[j].len += mcfg->memseg[j].hugepage_sz;
    hugepage[i].memseg_id = j;
}