sendfile and page usage statistics

[Igor Sysoev]

On Tue, Oct 09, 2007 at 04:50:01PM +0400, Igor Sysoev wrote:

> As I understand if sendfile() with hardware TX chsum or TSO are used,
> then CPU does not touch file pages at all. So pagedaemon never set
> PG_REFERENCED to vnode object pages while scanning them.
> Does VM set PG_REFERENCED by another way ? Otherwise, often used files
> that accessed by sendfile() only have small chances to be cached by VM.

I have looked kern_sendfile() in CURRENT and it seems to me that
PG_REFERENCED is never set when sendfile() gets cached vm_page.
I have looked the code path:

vm_page_grab()
    vm_page_lookup()
    vm_page_wire()
sf_buf_alloc() on i386 and amd64

and have not seen PG_REFERENCED.


-- 
Igor Sysoev
http://sysoev.ru/en/