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Date:      Fri, 30 Oct 2020 17:32:08 -0700
From:      Matthew Macy <mmacy@freebsd.org>
To:        freebsd-current <freebsd-current@freebsd.org>
Subject:   Re: OpenZFS: kldload zfs.ko freezes on i386 4GB memory
Message-ID:  <CAPrugNqPQEk=Wt6GogeZOD0Yt4H2xOasS0TkOum501T9tSVmJw@mail.gmail.com>
In-Reply-To: <CAPrugNoYZS4wcyrpQ0584jZM1zTnwds7rCQPtm5ahJ8Gm91H1A@mail.gmail.com>
References:  <E1kWvLj-0000GY-Ic.qroxana-mail-ru@smtp29.i.mail.ru> <202010300313.09U3D0KZ006216@slippy.cwsent.com> <20201030204622.GF2033@zxy.spb.ru> <202010302053.09UKrAXc031272@slippy.cwsent.com> <20201030220809.GG2033@zxy.spb.ru> <202010302234.09UMYA5d032018@slippy.cwsent.com> <20201030224734.GH2033@zxy.spb.ru> <202010302300.09UN0t4A032372@slippy.cwsent.com> <20201030233138.GD34923@zxy.spb.ru> <202010302350.09UNoVcM033686@slippy.cwsent.com> <CAPrugNoYZS4wcyrpQ0584jZM1zTnwds7rCQPtm5ahJ8Gm91H1A@mail.gmail.com>

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>
> Getting back to your original question. A more efficient ARC would exercise
> your memory more intensely because you are replacing disk reads with memory
> reads. And as I said before the old ZFS "found" weak RAM on three separate
> occasions in three different machines over the last ten years. You're
> advised to replace the marginal memory.

Ryan has been able to reproduce this in a VM with 4GB, similarly a VM
with 2GB loads just fine. It would seem that 4GB triggers a bug in
limit handling. We're hoping that we can simply lower one of the
default limits on i386 and make the problem go away.

Please don't shoot the messenger when I observe that, generally
speaking, i386 is considered a self supported platform due to ZFS
general inability to perform well with limited memory or KVA. Long
mode has been available on virtually all processors shipped since
2006.

Cheers.
-M



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