Date: Wed, 10 Oct 2007 12:34:36 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Igor Sysoev <is@rambler-co.ru> Cc: freebsd-current@freebsd.org, Antony Mawer <fbsd-current@mawer.org> Subject: Re: sendfile and page usage statistics Message-ID: <20071010093436.GB2180@deviant.kiev.zoral.com.ua> In-Reply-To: <20071010062541.GA23840@rambler-co.ru> References: <20071009125001.GC5758@rambler-co.ru> <20071010055748.GA18931@rambler-co.ru> <20071010060605.GB18931@rambler-co.ru> <470C6DD4.1060509@mawer.org> <20071010062541.GA23840@rambler-co.ru>
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--Iy2CUD6FdotTkhwY Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Oct 10, 2007 at 10:25:41AM +0400, Igor Sysoev wrote: > On Wed, Oct 10, 2007 at 04:14:44PM +1000, Antony Mawer wrote: >=20 > > 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 fil= es > > >>>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,= =20 > > > xfsize)) > > >+ vm_page_flag_set(pg, PG_REFERENCED); > > > VM_OBJECT_UNLOCK(obj); > > > else if (m !=3D NULL) > >=20 > > You are missing opening/closing braces on your if() statement with this= =20 > > change... >=20 > Oh, thank you! You have saved me from coredump. > This is why in my coding style I always use braces for single statement= =20 > inside if(). Also, as a minimum you need to brace the vm_page_flag_set() with vm_page_lock_queues()/vm_page_unlock_queues(). But I think that the actual patch is wrong. The PG_REFERENCED bit shall be set when hardware access bit is set on pte. You patch would set it in advance. --Iy2CUD6FdotTkhwY Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFHDJysC3+MBN1Mb4gRAj+WAKCQNdZT728t4t7msPeDwic0+0NSaQCeIlGk TfSYvOp0XNmAtrxVuZMgjNM= =yxUs -----END PGP SIGNATURE----- --Iy2CUD6FdotTkhwY--
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