Date: Mon, 22 Jan 2024 07:15:22 -0600 From: Mike Karels <karels@freebsd.org> To: Alexey Dokuchaev <danfe@freebsd.org>, Jessica Clarke <jrtc27@freebsd.org> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 636592343c3e - main - tmpfs: increase memory reserve to a percent of available memory + swap Message-ID: <04794665-EFCA-4E89-9956-B18684898C9D@freebsd.org> In-Reply-To: <Za3ldgmM-nbPNdxe@FreeBSD.org> References: <202312191534.3BJFY3fo030908@gitrepo.freebsd.org> <FCB7B75C-1816-4F93-9560-59208F5A8781@freebsd.org> <Za3ldgmM-nbPNdxe@FreeBSD.org>
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On 21 Jan 2024, at 21:48, Alexey Dokuchaev wrote: > On Mon, Jan 22, 2024 at 03:27:57AM +0000, Jessica Clarke wrote: >> On 19 Dec 2023, at 15:34, Mike Karels <karels@FreeBSD.org> wrote: >>> commit 636592343c3ec0feb61a4d8043676381384420dd >>> >>> tmpfs: increase memory reserve to a percent of available memory + swap >>> >>> [...] >>> >>> Add sysctl for vfs.tmpfs.memory_percent and the pre-existing >>> vfs.tmpfs.memory_reserved to tmpfs(5). >>> >>> PR: 275436 >>> MFC after: 1 month >>> Reviewed by: rgrimes >>> Differential Revision: https://reviews.freebsd.org/D43011 >> >> I just got: >> >> make[6]: Could not create temporary file /tmp/makeDl4i9S: >> No space left on device >> >> after doing a buildworld -j4 on a 4 core, 16 GiB system where /tmp is a >> tmpfs, with the prior buildworld having taken me past this commit, >> which I strongly suspect to be the cause. Whilst I understand the >> motivation behind your commits, this is a sad regression to have; it's >> not exactly a particularly strange situation. Bug 276402 is about the interaction of this change with ZFS ARC, which seems to be problematical. I spent some time investigating yesterday. Depending on the dynamics, I get different results. If tmpfs grows, the ARC will be reduced if needed. But if the ARC grows to the point that tmpfs sets free space to 0 or quite low, attempts to write to tmpfs fail without any reduction in ARC. Jess, two quesions: 1. Are you using ZFS on this system? 2. Can you try with vfs.tmpfs.memory_percent set to 100? > FWIW, I've seen two people complain about this last week, apparently > this kernel OOM protection doesn't work very well. :-/ So far, I have only seen OOM kills when memory + swap are quite short, with a tmpfs memory_percent above 95. But with ZFS, it can happen when the ARC could have been reduced. I will investigate more today. If I don't find a way to resolve this, I'll probably commit a change to set vfs.tmpfs.memory_percent to 100 by default, at least for now, and if that works around the problem. Mike
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