Date: Sat, 23 Jun 2018 07:49:53 -0700 From: Mark Millard <marklmi@yahoo.com> To: Trev <freebsd-arm@sentry.org> Cc: freebsd-arm <freebsd-arm@freebsd.org>, bob prohaska <fbsd@www.zefox.net> Subject: Re: GPT vs MBR for swap devices Message-ID: <03C2D3C4-6E90-4054-AF79-BD7FE2B7958D@yahoo.com> In-Reply-To: <20180623143218.GA6905@www.zefox.net> References: <25F1A4BA-FBFC-4C32-85DD-5F5BA71A2B1A@yahoo.com> <20180620023253.GA89924@www.zefox.net> <a232ed45-a9a9-1017-72ed-720a6c7a8f03@sentry.org> <1D86911D-20D1-494A-822B-1C07C5598CB1@yahoo.com> <10CAC122-399D-459E-9153-ABD7E753777E@yahoo.com> <a2d7f4d3-0b6d-f82d-bae8-0988b0b54a8f@sentry.org> <20180623143218.GA6905@www.zefox.net>
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On 2018-Jun-23, at 7:32 AM, bob prohaska <fbsd at www.zefox.net> wrote: > On Fri, Jun 22, 2018 at 12:08:56PM +1000, Trev wrote: >>=20 >>=20 >> Unfortunately my rpi3B+ is not a direct comparison with the rpi2B=20 >> because I only had the one USB2 memory device holding /usr, /usr/obj = and=20 >> swap. I'll try moving swap to a dedicated USB2 memory device. >=20 > Have you considered putting a swapfile on the microSD card? That's one > of the things I have not tried. A swap partition on SD seems to work.=20= > A swapfile is easier to try and may work.=20 See: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D206048 for why I would not recommend using a swap file. In particular comment 7 is a quote: > On 2017-Feb-13, at 7:20 PM, Konstantin Belousov <kostikbel at = gmail.com> wrote > on the freebsd-arm list: >=20 > . . . >=20 > swapfile write requires the write request to come through the = filesystem > write path, which might require the filesystem to allocate more memory > and read some data. E.g. it is known that any ZFS write request > allocates memory, and that write request on large UFS file might = require > allocating and reading an indirect block buffer to find the block = number > of the written block, if the indirect block was not yet read. >=20 > As result, swapfile swapping is more prone to the trivial and = unavoidable > deadlocks where the pagedaemon thread, which produces free memory, = needs > more free memory to make a progress. Swap write on the raw partition = over > simple partitioning scheme directly over HBA are usually safe, while = e.g. > zfs over geli over umass is the worst construction. Comment 3 from Tom Vijlbrief even reports a way to reproduce such a problem with swap files: > This is not related to ARM or USB, I can reproduce it in a VirtualBox = amd64 client with the standard emulated hard disk. >=20 > . . . >=20 > stress -d 2 -m 3 --vm-keep >=20 > will hang the system as well. (This was on 2016-Jan-22.) Another reproduction report is Comment 5 from Sevan Janiyan: > In my case, to reproduce the behaviour, boot PI, add swap file as per = handbook instructions[1], run cat /somefile > /someotherfile >=20 > In this case /somefile is a 4GB file containing garbage from = /dev/urandom =3D=3D=3D Mark Millard marklmi at yahoo.com ( dsl-only.net went away in early 2018-Mar)
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