Date: Wed, 9 Nov 2011 17:25:42 -0800 From: Alfred Perlstein <alfred@freebsd.org> To: Paul Saab <ps@mu.org> Cc: Bruce Cran <bruce@cran.org.uk>, Ed Schouten <ed@80386.nl>, freebsd-arch@freebsd.org, Jilles Tjoelker <jilles@stack.nl>, arch@freebsd.org Subject: Re: [PATCH] fadvise(2) system call Message-ID: <20111110012542.GA6110@elvis.mu.org> In-Reply-To: <CAMYpurzXM3Yeko_LxtsdKgPsGPKW75W2cUFUq59oSb=CcAqqMA@mail.gmail.com> References: <201110281426.00013.jhb@freebsd.org> <4EB2C9DD.9090606@FreeBSD.org> <20111104160319.GD6110@elvis.mu.org> <201111080800.32717.jhb@freebsd.org> <4EBB104F.5010000@cran.org.uk> <CAMYpurzXM3Yeko_LxtsdKgPsGPKW75W2cUFUq59oSb=CcAqqMA@mail.gmail.com>
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* Paul Saab <ps@mu.org> [111109 16:32] wrote: > On Wed, Nov 9, 2011 at 3:44 PM, Bruce Cran <bruce@cran.org.uk> wrote: > > On 08/11/2011 13:00, John Baldwin wrote: > >> > >> I think it would be fine to add flags to applications like 'tar' to allow > >> users to alter their behavior in specific use cases when it makes sense. > >> However, I think there are more workloads for 'tar' than the ones you are > >> thinking of and we should be hesitant to change applications to use non- > >> default settings. > > > > Someone's done that for GNU tar on Linux, adding a --no-oscache switch: > > http://www.mysqlperformanceblog.com/2010/04/02/fadvise-may-be-not-what-you-expect/ > > So adding this support is good, but not for general purpose. It's > really only good when you're pumping gigs of data through tar. I did > this for libarchive (plus other work for O_DIRECT reading and > creating the archive) for copying large amounts of data without > impacting a running system.. It worked great for this, but then it > absolutely fails when extracting a tar archive with millions of little > files because of all the sync operations. I've thought about this and it almost makes sense to have a secondary LRU that such pages would wind up in that is much smaller than the system one. I'm pretty sure there are a number of papers on this, but I've not looked over them in a long while. > > Anyway, this is a good option to enable and has very practical uses > out there, but it should be turned on with an option and not on by > default. What about the operation of just reading the tar archive itself? -- - Alfred Perlstein .- VMOA #5191, 03 vmax, 92 gs500, 85 ch250, 07 zx10 .- FreeBSD committer
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