Date: Thu, 23 Jun 2011 04:58:43 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: John Baldwin <jhb@FreeBSD.org> Cc: src-committers@FreeBSD.org, Alan Cox <alc@FreeBSD.org>, svn-src-all@FreeBSD.org, "Bjoern A. Zeeb" <bz@FreeBSD.org>, Bruce Evans <brde@optusnet.com.au>, svn-src-head@FreeBSD.org Subject: Re: svn commit: r223307 - head/sys/vm Message-ID: <20110623045454.U1550@besplex.bde.org> In-Reply-To: <201106220948.02421.jhb@freebsd.org> References: <201106191913.p5JJDOqJ006272@svn.freebsd.org> <BBC34F79-FFA7-4A05-83B3-DE17E0AB14D0@FreeBSD.org> <20110622063258.D2275@besplex.bde.org> <201106220948.02421.jhb@freebsd.org>
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On Wed, 22 Jun 2011, John Baldwin wrote: > On Tuesday, June 21, 2011 4:58:10 pm Bruce Evans wrote: >> On Tue, 21 Jun 2011, Bjoern A. Zeeb wrote: >>> ... >>> vm_page.o: In function `vm_page_clear_dirty': >>> /sys/vm/vm_page.c:(.text+0x18d0): undefined reference to `atomic_clear_8' >>> /sys/vm/vm_page.c:(.text+0x18d0): relocation truncated to fit: R_MIPS_26 against `atomic_clear_8' >>> vm_page.o: In function `vm_page_set_validclean': >>> /sys/vm/vm_page.c:(.text+0x38f0): undefined reference to `atomic_clear_8' >>> /sys/vm/vm_page.c:(.text+0x38f0): relocation truncated to fit: R_MIPS_26 against `atomic_clear_8' >> >> Atomic types shorter than int cannot be used in MI code, since they might >> not exist. Apparently they don't exist on mips. jake@ fixed all their >> old uses for sparc4 in ~Y2K. > > I agree. Is there any harm in having the 'dirty' and 'valid' fields in > vm_page always be at least of size 'int'? > > In the case of amd64, vm_page would change from a size of 120 bytes to 128. > > On i386 I think you'd end up changing the size from 68 to 76. > > (Using an int results in alignment padding after 'busy'.) That is quite a bit. Perhaps the struct should be packed better so that each char -> int expansion takes <= 3 bytes instead of >= 4. The expansion might even be negative. It is only moderately well packed now. > Hmm, that's around 120k of extra vm_page_t space for a machine with 64M of > RAM, so around 0.18% of RAM would be used on both platforms (presumably the > usage would be similar on other platforms as well). At 24 GB of RAM, the > extra space is just under 0.20% of RAM (48M). Bruce
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