从最近的linux / Documentation / sysctl / fs.txt：@H_404_3@

file-max and file-nr:@H_404_3@

The kernel allocates file handles dynamically,but as yet it doesn’t
free them again.@H_404_3@

The value in file-max denotes the maximum number of file- handles that
the Linux kernel will allocate. When you get lots of error messages
about running out of file handles,you might want to increase this
limit.@H_404_3@

Historically,the three values in file-nr denoted the number of
allocated file handles,the number of allocated but unused file
handles,and the maximum number of file handles. Linux 2.6 always
reports 0 as the number of free file handles — this is not an error,
it just means that the number of allocated file handles exactly
matches the number of used file handles.@H_404_3@

Attempts to allocate more file descriptors than file-max are reported
with printk,look for “VFS: file-max limit reached”.@H_404_3@

2.6内核使用经验法则来根据系统中的内存量来设置file-max. 2.6内核中fs / file_table.c的片段：@H_404_3@

/*
 * 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;
files_stat.max_files = max_t(unsigned long,n,NR_FILE);

files_stat.max_files是fs.file-max的设置.对于每1公斤的公羊,最终大约为100(10％)@H_404_3@