Date: Wed, 10 Oct 2007 10:06:06 +0400 From: Igor Sysoev <is@rambler-co.ru> To: freebsd-current@freebsd.org Subject: Re: sendfile and page usage statistics Message-ID: <20071010060605.GB18931@rambler-co.ru> In-Reply-To: <20071010055748.GA18931@rambler-co.ru> References: <20071009125001.GC5758@rambler-co.ru> <20071010055748.GA18931@rambler-co.ru>
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On Wed, Oct 10, 2007 at 09:57:48AM +0400, Igor Sysoev wrote:
> 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.
As I understand the following patch against uipc_syscalls.c
should fix the bug to some extent:
if (pg->valid && vm_page_is_valid(pg, pgoff, xfsize))
+ vm_page_flag_set(pg, PG_REFERENCED);
VM_OBJECT_UNLOCK(obj);
else if (m != NULL)
--
Igor Sysoev
http://sysoev.ru/en/
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