mmap performance and memory use

Alan Cox alc at
Tue Oct 25 23:35:36 UTC 2011

On 10/10/2011 4:28 PM, Wojciech Puchar wrote:
>> Notice that vm.pmap.pde.promotions increased by 31.  This means that 
>> 31 superpage mappings were created by promotion from small page 
>> mappings.
> thank you. i looked at .mappings as it seemed logical for me that is 
> shows total.
>> In contrast, vm.pmap.pde.mappings counts superpage mappings that are 
>> created directly and not by promotion from small page mappings.  For 
>> example, if a large executable, such as gcc, is resident in memory, 
>> the text segment will be pre-mapped using superpage mappings, 
>> avoiding soft fault and promotion overhead.  Similarly, mmap(..., 
>> MAP_PREFAULT_READ) on a large, memory resident file may pre-map the 
>> file using superpage mappings.
> your options are not described in mmap manpage nor madvise 
> when can i find the up to date manpage or description?

A few minutes ago, I merged the changes to support and document 
MAP_PREFAULT_READ into 8-STABLE.  So, now it exists in HEAD, 9.0, and 


More information about the freebsd-hackers mailing list