Date: Wed, 10 Oct 2007 10:25:41 +0400 From: Igor Sysoev <is@rambler-co.ru> To: Antony Mawer <fbsd-current@mawer.org> Cc: freebsd-current@freebsd.org Subject: Re: sendfile and page usage statistics Message-ID: <20071010062541.GA23840@rambler-co.ru> In-Reply-To: <470C6DD4.1060509@mawer.org> References: <20071009125001.GC5758@rambler-co.ru> <20071010055748.GA18931@rambler-co.ru> <20071010060605.GB18931@rambler-co.ru> <470C6DD4.1060509@mawer.org>
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On Wed, Oct 10, 2007 at 04:14:44PM +1000, Antony Mawer wrote: > On 10/10/2007 4:06 PM, Igor Sysoev wrote: > >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) > > You are missing opening/closing braces on your if() statement with this > change... Oh, thank you! You have saved me from coredump. This is why in my coding style I always use braces for single statement inside if(). -- Igor Sysoev http://sysoev.ru/en/
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