Date: Mon, 4 Sep 2023 18:39:32 -0700 From: Mark Millard <marklmi@yahoo.com> To: Alexander Motin <mav@FreeBSD.org> Cc: dev-commits-src-main@freebsd.org, Current FreeBSD <freebsd-current@freebsd.org> Subject: Re: An attempted test of main's "git: 2ad756a6bbb3" "merge openzfs/zfs@95f71c019" that did not go as planned Message-ID: <5724006A-F4C4-42CA-98A9-90C5EB914F5E@yahoo.com> In-Reply-To: <5605506b-5059-fb72-3e5a-741863d54444@FreeBSD.org> References: <F20BD354-2E10-4CD9-88FB-99DB1E405A52.ref@yahoo.com> <F20BD354-2E10-4CD9-88FB-99DB1E405A52@yahoo.com> <c9c5096b-33d9-1cb6-d446-97b99f324fce@FreeBSD.org> <673A446E-6F94-451E-910F-079F678C5289@yahoo.com> <2BDD30B5-6248-4EC3-83C8-0499E0717D1D@yahoo.com> <C78808EB-FDE2-432D-8309-A7017DFC1BCE@yahoo.com> <69028684-c2cd-8f0c-617f-d0763c08dbe4@FreeBSD.org> <8D832756-6754-4D1E-AE8D-E716FE08F747@yahoo.com> <5605506b-5059-fb72-3e5a-741863d54444@FreeBSD.org>
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On Sep 4, 2023, at 10:05, Alexander Motin <mav@FreeBSD.org> wrote: > On 04.09.2023 11:45, Mark Millard wrote: >> On Sep 4, 2023, at 06:09, Alexander Motin <mav@FreeBSD.org> wrote: >>> per_txg_dirty_frees_percent is directly related to the delete delays = we see here. You are forcing ZFS to commit transactions each 5% of = dirty ARC limit, which is 5% of 10% or memory size. I haven't looked on = that code recently, but I guess setting it too low can make ZFS commit = transactions too often, increasing write inflation for the underlying = storage. I would propose you to restore the default and try again. >> While this machine is different, the original problem was worse than >> the issue here: the load average was less than 1 for the most part >> the parallel bulk build when 30 was used. The fraction of time = waiting >> was much longer than with 5. If I understand right, both too high and >> too low for a type of context can lead to increased elapsed time and >> getting it set to a near optimal is a non-obvious exploration. >=20 > IIRC this limit was modified several times since originally = implemented. May be it could benefit from another look, if default 30% = is not good. It would be good if generic ZFS issues like this were = reported to OpenZFS upstream to be visible to a wider public. = Unfortunately I have several other project I must work on, so if it is = not a regression I can't promise I'll take it right now, so anybody else = is welcome. As I understand, there are contexts were 5 is inappropriate and 30 works fairly well: no good single answer as to what value range will avoid problems. >> An overall point for the goal of my activity is: what makes a >> good test context for checking if ZFS is again safe to use? >> May be other tradeoffs make, say, 4 hardware threads more >> reasonable than 32. >=20 > Thank you for your testing. The best test is one that nobody else = run. It also correlates with the topic of "safe to use", which also = depends on what it is used for. :) Looks like use of a M.2 Samsung SSD 960 PRO 1TB with a non-debug FreeBSD build is suitable for the bulk -a -J128 test (no ALLOW_MAKE_JOBS variants enabled, USE_TMPFS=3Dno in use) on the 32 hardware thread system. (The swap partition in use is from the normal environment's PCIe Optane media.) The %idle and the load averages and %user stayed reasonable in a preliminary test. One thing it does introduce is trim management (both available and potentially useful). (Optane media does not support or need it.) No per_txg_dirty_frees_percent adjustment involved (still 5). I've learned to not use ^T for fear of /bin/sh aborting and messing up poudriere's context. So I now monitor with: # poudriere status -b in a separate ssh session. I'll note that I doubt I'd try for a complete bulk -a . I'd probably stop it if I notice that the number of active builders drops off for a notable time (normal waiting for prerequisites appearing to be why). =3D=3D=3D Mark Millard marklmi at yahoo.com
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