Date: Mon, 4 Jul 2016 21:26:06 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-hackers@freebsd.org Subject: Re: ZFS ARC and mmap/page cache coherency question Message-ID: <7e00af5a-86cd-25f8-a4c6-2d946b507409@denninger.net> In-Reply-To: <155b84da0aa.ad3af0e6139335.8627172617037605875@nextbsd.org> References: <20160630140625.3b4aece3@splash.akips.com> <CALXu0UfxRMnaamh%2Bpo5zp=iXdNUNuyj%2B7e_N1z8j46MtJmvyVA@mail.gmail.com> <20160703123004.74a7385a@splash.akips.com> <155afb8148f.c6f5294d33485.2952538647262141073@nextbsd.org> <45865ae6-18c9-ce9a-4a1e-6b2a8e44a8b2@denninger.net> <155b84da0aa.ad3af0e6139335.8627172617037605875@nextbsd.org>
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[-- Attachment #1 --] On 7/4/2016 18:45, Matthew Macy wrote: > > > ---- On Sun, 03 Jul 2016 08:43:19 -0700 Karl Denninger <karl@denninger.net> wrote ---- > > > > On 7/3/2016 02:45, Matthew Macy wrote: > > > > > > Cedric greatly overstates the intractability of resolving it. Nonetheless, since the initial import very little has been done to improve integration, and I don't know of anyone who is up to the task taking an interest in it. Consequently, mmap() performance is likely "doomed" for the foreseeable future.-M---- > > > > Wellllll.... > > > > I've done a fair bit of work here (see > > https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=187594) and the > > political issues are at least as bad as the coding ones. > > > > > Strictly speaking, the root of the problem is the ARC. Not ZFS per se. Have you ever tried disabling MFU caching to see how much worse LRU only is? I'm not really convinced the ARC's benefits justify its cost. > > -M > The ARC is very useful when it gets a hit as it avoid an I/O that would otherwise take place. Where it sucks is when the system evicts working set to preserve ARC. That's always wrong in that you're trading a speculative I/O (if the cache is hit later) for a *guaranteed* one (to page out) and maybe *two* (to page back in.) -- Karl Denninger karl@denninger.net <mailto:karl@denninger.net> /The Market Ticker/ /[S/MIME encrypted email preferred]/ [-- Attachment #2 --] 0 *H 010 `He 0 *H _0[0C)0 *H 01 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1"0 *H Cuda Systems LLC CA0 150421022159Z 200419022159Z0Z1 0 UUS10UFlorida10U Cuda Systems LLC1 0 UKarl Denninger (OCSP)0"0 *H 0 X@vkY Tq/vE]5#֯MX \8LJ/V?5Da+ sJc*/r{ȼnS+ w")ąZ^DtdCOZ ~7Q '@a#ijc۴oZdB&!Ӝ-< ? HN5y 5}F|e f"V لio74zn">a1qWuɖbFeGE&3(KhixG3!#e_XƬ Ϝ/,$+;4y 'Bz<qT9_?rRUpn5 Jn&Rx/p Jyel*pN8/#9u/YP EC)TY>~/˘N[vyiDKˉ ,^" ?$T8 v& K%z8C @?K{9f`+@,| Mbia 007++0)0'+0http://cudasystems.net:88880 U 0 0 `HB0 U 0, `HB OpenSSL Generated Certificate0 U -h\Ff Y0 U #0$q}ݽʒm50 U 0karl@denninger.net0 *H Owbabɺx&Uk[ (Oj!%p MQ0I!#QH}.>~2&D}<wm_>V6 v ]f>=Nn+8;q wfΰ/RLyUG#b}n!Dր _up|_ǰc/%ۥ nN8:d;-UJd/m1~VނיnN I˾$tF1&}|?q?\đXԑ&\4V<lKۮ3%Am_(q -(cAeGX)f}-˥6cv~Kg8m~v ;|9:-iAPқ6ېn-.)<[$KJtt/L4ᖣ^Cmu4vb{+BG$M0c\[MR|0FԸP&78"4p# }D Z9;V9#>Sw"[UP710001 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1"0 *H Cuda Systems LLC CA)0 `He M0 *H 1 *H 0 *H 1 160705022606Z0O *H 1B@uXtwl a:lPUF H^EN[BN%vbkN_?w/}X0l *H 1_0]0 `He*0 `He0 *H 0*H 0 *H @0+0 *H (0 +71001 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1"0 *H Cuda Systems LLC CA)0 *H 101 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1"0 *H Cuda Systems LLC CA)0 *H ^c硿6pT_ U#4֪@95ܶ|'j q~g`LCH~M܊0"2y{%I ᅐPL! ^9ymZҡmJg @P_%jԜ \2zAo k R6~asND g1튮oTxYh{nkӀO7ZOM\ t&Vä|^+ݹ Hr i4[6 TTA%}GVhtzyPZF 2'萧z/xO18c,60,7g$4a(+ 9@E-E{4L9~[qza{y`b%,) 6 <0e<?hP& *ipDKltuQoFFA i=G n2' ) Bf~c%M>l:R*\C
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