Date: Fri, 2 Mar 2018 18:18:16 -0700 From: Warner Losh <imp@bsdimp.com> To: bob prohaska <fbsd@www.zefox.net> Cc: Ian Lepore <ian@freebsd.org>, Mike <the.lists@mgm51.com>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: Is maximum swap usage tunable? Message-ID: <CANCZdfomeV_5Ynf7FhSDg20-=XzdD8fQJ5EVC7ZV=6jYteMrDA@mail.gmail.com> In-Reply-To: <20180303004315.GB37148@www.zefox.net> References: <20180228170311.GA26187@www.zefox.net> <a759ecea-83f4-b0b2-7113-c39633f68637@mgm51.com> <20180228185517.GB26187@www.zefox.net> <8f422161-885e-aa91-eacd-018540222d65@mgm51.com> <20180228214301.GA29481@www.zefox.net> <b82801b8-bc29-414c-1170-621bb4a5d937@mgm51.com> <CANCZdfq_MpxjUyVd-=%2BMiAQAER4TeDh9irhx_evdXwa3yt3h0g@mail.gmail.com> <1520010957.23690.10.camel@freebsd.org> <20180303004315.GB37148@www.zefox.net>
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On Fri, Mar 2, 2018 at 5:43 PM, bob prohaska <fbsd@www.zefox.net> wrote: > On Fri, Mar 02, 2018 at 10:15:57AM -0700, Ian Lepore wrote: > > > You forgot a cause: (5) swap is on an sdcard where taking 30-90 seconds > > to complete an IO is "normal". > > > FWIW, the Sandisk Extreme USB flash drive is claimed to be considerably > faster than that, ~2MB/sec random write, at least per > http://usb.userbenchmark.com/SanDisk-Extreme-USB-30-16GB/Rating/1301 > One hopes(!) that the microSD cards of the same name are simlar. Hope in one hand and spit in the other and see which one gets wet first :) The problem isn't the steady-state happy-state streaming pictures/video to the card. The problem is that sometimes the "long tail" times for the I/O for pathological cases can be seconds, or tends of seconds. It doesn't take too many of those high-latency I/Os to really screw up the system.... SD card FTLs are 'go fast for streaming video / pictures, suck slow for everything else'. Consumer grade SSDs, though they also have kinda crappy FTLs, aren't anywhere near that bad. Warner
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