【infiniband】关于contig的支持
contig的英文翻译是：n.重叠群；叠连群；片段重叠群。
有个叫Contig的小工具，是一个单个文件碎片整理程序，其目的是使磁盘上的文件保持连续。
在读perfest源码时，看到is_contig_supported。
内核mm\page_alloc.c文件中有个__alloc_contig_pages函数，Linux内存管理：大页内存原理 - 知乎 (zhihu.com) 。
perfest相关代码：
ctx_init函数中：
if (user_param->use_hugepages) {ctx->is_contig_supported = FAILURE;} else {ctx->is_contig_supported = check_for_contig_pages_support(ctx->context);}create_single_mr函数中：
#ifdef HAVE_VERBS_EXPexp_flags |= IBV_EXP_ACCESS_ALLOCATE_MR;#ifdef HAVE_VERBS_EXPif (ctx->is_contig_supported == SUCCESS || user_param->use_odp) {reg_mr_exp_in.pd = ctx->pd;reg_mr_exp_in.addr = ctx->buf[qp_index];reg_mr_exp_in.length = ctx->buff_size;reg_mr_exp_in.exp_access = exp_flags;reg_mr_exp_in.comp_mask = 0;ctx->mr[qp_index] = ibv_exp_reg_mr(®_mr_exp_in);}Contiguous Pages
Contiguous Pages improves performance by allocating user memory regions over physical contiguous pages. It enables a user application to ask low level drivers to allocate contiguous memory for it as part of ibv_reg_mr.
Additional performance improvements can be reached by allocating Queue Pair (QP) and Completion Queue (CQ|) buffers to the Contiguous Pages.
"Contiguous Pages"是一种内存管理技术，它通过将用户内存区域分配到物理连续的内存页上来提高性能。这使得用户应用程序可以要求低级驱动程序为其分配连续的内存，作为ibv_reg_mr的一部分。通过将队列对（QP）和完成队列（CQ）缓冲区分配给Contiguous Pages，可以实现额外的性能改进。
To activate set the below environment variables with values of PREFER_CONTIG or CONTIG.
- For QP: MLX_QP_ALLOC_TYPE
- For CQ: MLX_CQ_ALLOC_TYPE
The following are all the possible values that can be allocated to the buffer:
| Possible Value | Description |
|---|---|
| ANON | Use current pages ANON small ones. |
| HUGE | Force huge pages. |
| CONTIG | Force contiguous pages. |
| PREFER_CONTIG | Try contiguous fallback to ANON small pages. (Default) |
| PREFER_HUGE | Try huge fallback to ANON small pages. |
| ALL | Try huge fallback to contiguous if failed fallback to ANON small pages. |
Note that values are NOT case sensitive.
Usage:
The application calls the ibv_exp_reg_mr API which turns on the IBV_EXP_ACCESS_ALLOCATE_MR bit and sets the input address to NULL. Upon success, the address field of the struct ibv_mr will hold the address to the allocated memory block. This block will be freed implicitly when the ibv_dereg_mr() is called.
The following are environment variables that can be used to control error cases/contiguity:
| Paramters | Description |
|---|---|
|
| Configures the allocator type.
|
|
| Sets the maximum contiguous block size order.
|
|
| Sets the minimum contiguous block size order.
|
参考：
Linux内存管理：大页内存原理 - 知乎 (zhihu.com)
GitHub - mai-lang-chai/Sysinternals: 微软开发的系统管理小工具-简约教程-含渗透利器
Contig 文件通过 Defrag | Microsoft Learn
Optimized Memory Access - MLNX_EN v4.9-5.1.0.0 LTS - NVIDIA Networking Docs
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