Date: Wed, 10 Oct 2007 16:14:44 +1000 From: Antony Mawer <fbsd-current@mawer.org> To: Igor Sysoev <is@rambler-co.ru> Cc: freebsd-current@freebsd.org Subject: Re: sendfile and page usage statistics Message-ID: <470C6DD4.1060509@mawer.org> In-Reply-To: <20071010060605.GB18931@rambler-co.ru> References: <20071009125001.GC5758@rambler-co.ru> <20071010055748.GA18931@rambler-co.ru> <20071010060605.GB18931@rambler-co.ru>
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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... --Antony
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