Date: Fri, 2 Mar 2018 11:19:16 -0500 From: Mike <the.lists@mgm51.com> Cc: freebsd-arm@freebsd.org Subject: Re: Is maximum swap usage tunable? Message-ID: <b82801b8-bc29-414c-1170-621bb4a5d937@mgm51.com> In-Reply-To: <20180228214301.GA29481@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>
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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]
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