NR_OPEN 與 NR_FILE 的差別

<a href="http://blog.chinaunix.net/uid-24807808-id-3077199.html">NR_OPEN 與 NR_FILE 的差別</a>

閱讀0.11版的核心源碼時，在linux-0.11/fs/pipe.c中，函數sys_pipe()裡面出現了2個宏定義，NR_OPEN 與 NR_FILE。下面說明一下它們的差別：

1. NR_OPEN is the maximum number of files that can be opened by process。

NR_OPEN是一個程序可以打開的最大檔案數。

A process cannot use more than NR_OPEN file descriptors.

一個程序不能使用超過NR_OPEN檔案描述符。

The kernel also enforces a dynamic bound on the maximum number of file descriptors in the signal-&lt;rlim[RLIMIT_NOFILE] structure of the process descriptor; this value is usually 1,024, but it can be raised if the process has root privileges.

2. NR_FILE is the limit on total number of files in the system at any given point in time

NR_FILE 是系統在某一給定時刻，限制的檔案總數

While initializing the kernel we setup the vfs cache with

start_kernel

vfs_caches_init(num_physpages);

files_init(mempages);

fs/file_table.c says

/* One file with associated inode and dcache is very roughly 1K.

* Per default don't use more than 10% of our memory for files.

n = (mempages * (PAGE_SIZE / 1024)) / 10;

this n can never be greater than NR_FILE

原文

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