Date: Fri, 2 Mar 2018 10:04:56 -0700 From: Warner Losh <imp@bsdimp.com> To: Mike <the.lists@mgm51.com> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: Is maximum swap usage tunable? Message-ID: <CANCZdfq_MpxjUyVd-=%2BMiAQAER4TeDh9irhx_evdXwa3yt3h0g@mail.gmail.com> In-Reply-To: <b82801b8-bc29-414c-1170-621bb4a5d937@mgm51.com> 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>
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On Fri, Mar 2, 2018 at 9:19 AM, Mike <the.lists@mgm51.com> wrote: > On 2/28/2018 4:43 PM, bob prohaska wrote: > > On Wed, Feb 28, 2018 at 02:37:36PM -0500, Mike wrote: > >> On 2/28/2018 1:55 PM, bob prohaska wrote: > >>> On Wed, Feb 28, 2018 at 12:20:56PM -0500, Mike wrote: > >>>> On 2/28/2018 12:03 PM, bob prohaska wrote: > >>>>> In watching system compilations on an RPi3 it looks as if the > >>>>> system starts killing processes with "out of swap" warnings > >>>>> well below 50% of full utilization (in this case, 2 GB). One > >>>>> recent instance of make -j4 kernel-toolchain killed llvm-tblgen > >>>>> with only 34% of the swap in use. > >>>>> > >>>>> Is the maximum swap usage limit adjustable in any way? I didn't > >>>>> recognize anything useful in the page at > >>>>> https://www.freebsd.org/cgi/man.cgi?query=sysctl(8)&; > sektion=&manpath=freebsd-release-ports > >>>>> > >>>>> It's possible the problem is really swap speed, rather than size, so > I'd > >>>>> like to try changing size limits if possible. The swap media claims > 2-3 > >>>>> MB/sec random write speed and observations with gstat seem to > support the > >>>>> claim, but transient stalls are hard to observe. An RPi2 with similar > >>>>> hardware seems to have no problems. > >>>>> > >>>> > >>>> > >>>>> It's possible the problem is really swap speed > >>>> > >>>> I was running into swap speed / timeout issues. There were messages > on > >>>> the console to that effect. > >>>> > >>>> Once I put the swap space on rotating rust, that part of the compile > >>>> problem disappeared. I use 1GB swap space. > >>>> > >>> > >>> The latest kernel versions seem to have largely done away with the > >>> "indefinite wait buffobj" warnings. They're few and far between, > >>> the compile proceeds unless they're abundant. The fact that armv7 > >>> has no problem, and the system is reporting "out of swap" with 34% > >>> in use strikes me as suspicious. Kernel and userland are in sync, > >>> so the figure of 34% swap usage is probably accurate. > >>> > >>> Perhaps my question is better phrased thus: How does FreeBSD-arm > >>> determine when it's out of swap? > >>> > >> > >> > >> Thanks for the follow-up. > >> > >> I was planning to download and try the > >> > >> RPI3-20180226-r330034 > >> > >> image file this evening. Per your comment, I'll not use the rusty swap > >> space, and see what happens. > >> > >> I'll report back, probably on the morrow... > >> > > FWIW, I've been using Sandisk Extreme USB 3 flash drives for > > /usr /var/ and swap on the Pi3. It seems that flash write > > speed is a tighter bottleneck than USB 2.0 ports on the Pi. > > Attempts to use older, slower USB 2 flash drives on a Pi2 > > didn't work, though the symptoms were never "out of swap". > > > > buildworld is still running. I started it around 3PM (EST) on March 1. > > I'm seeing a lot of swap messages on the console. The text is: > > swap_pager: indefinite wait buffer: bufobj: 0, > blkno: [varies], size: [varies] This message comes from the swap pager when the I/O doesn't complete quickly enough. It has nothing to do with sizes of the swap space. I've seen three causes for this: (1) The driver going crazy and not completing I/Os it gets notified as being done; (2) The driver not having a backstop timer on I/Os to fail them with timeout; (3) timeouts not firing for the driver to fail the I/O up the stack. (4) when a drive suddenly slow way way down (~100x or more slower), the I/O queues balloons and you can get these. Warner
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