From nobody Tue Jun 04 21:14:41 2024 X-Original-To: freebsd-arch@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4Vv3JM2xC5z5MbRC for ; Tue, 04 Jun 2024 21:14:43 +0000 (UTC) (envelope-from 0100018fe51aad3b-ef6075b1-1ecc-4c88-9f2c-60602d2a7958-000000@amazonses.com) Received: from a8-13.smtp-out.amazonses.com (a8-13.smtp-out.amazonses.com [54.240.8.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4Vv3JM1GfKz4rRj for ; Tue, 4 Jun 2024 21:14:43 +0000 (UTC) (envelope-from 0100018fe51aad3b-ef6075b1-1ecc-4c88-9f2c-60602d2a7958-000000@amazonses.com) Authentication-Results: mx1.freebsd.org; none DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=dqtolf56kk3wpt62c3jnwboqvr7iedax; d=tarsnap.com; t=1717535682; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From:In-Reply-To:Content-Type:Content-Transfer-Encoding; bh=g1x0/FoIMb3JAng8cMSrucq/+V9ZU/KvSkVl8EJBAvk=; b=Q0e2ZkjY33iGh+uFC1Al3c3a12GybyWHWSxwcBB4TfRhyAdGLIE0ZfYjWx9IzeJ8 UKU2P7Vbv4R/Yll+KFttb8du92U0Yq1od9N2tFoHqS3RVghuBpqVWeEg4JL6sxLa9EE +UMEDIhfYeFpyKEu/RAj+0MkA5NKQco7X/HGqvlM= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=ug7nbtf4gccmlpwj322ax3p6ow6yfsug; d=amazonses.com; t=1717535682; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From:In-Reply-To:Content-Type:Content-Transfer-Encoding:Feedback-ID; bh=g1x0/FoIMb3JAng8cMSrucq/+V9ZU/KvSkVl8EJBAvk=; b=dVwcJBaTSvSoTx8G5bmPX0N1JETh1/xKsRluWztbw6ego0UsQZTbgijidrqaAoDs HCZCmCk/pN9PaOVubaxWI/FsbcOX2aoQ5jr3oLkqVDZ3637SL375B0F8g96veB1ctBU W8F3oMbVu8kh+3OGrdID5dxbEi/Dm3avUNfEUYJY= Message-ID: <0100018fe51aad3b-ef6075b1-1ecc-4c88-9f2c-60602d2a7958-000000@email.amazonses.com> Date: Tue, 4 Jun 2024 21:14:41 +0000 List-Id: Discussion related to FreeBSD architecture List-Archive: https://lists.freebsd.org/archives/freebsd-arch List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-arch@FreeBSD.org MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: removing support for kernel stack swapping To: Poul-Henning Kamp , Konstantin Belousov Cc: John Baldwin , Mark Johnston , freebsd-arch@freebsd.org References: <6ddedba5-fc2f-4caa-aab5-bd29ca4fdf0b@FreeBSD.org> <202406042043.454Kh2ls009155@critter.freebsd.dk> Content-Language: en-US From: Colin Percival Autocrypt: addr=cperciva@tarsnap.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Feedback-ID: ::1.us-east-1.Lv9FVjaNvvR5llaqfLoOVbo2VxOELl7cjN0AOyXnPlk=:AmazonSES X-SES-Outgoing: 2024.06.04-54.240.8.13 X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:14618, ipnet:54.240.8.0/21, country:US] X-Rspamd-Queue-Id: 4Vv3JM1GfKz4rRj On 6/4/24 13:43, Poul-Henning Kamp wrote: > Many years ago I asked the then VM-wizards if we could have a global > kernel integer variable with a "VM-state-of-the-system" so caches > could modulate their behavior. > > Having something as simple as: > > 0 - free pizza > 1 - dont make it worse > 2 - please help > > would enable most of the caches in the kernel pull the right direction > before things get too critical. That might work, but it's important to have sufficient hysteresis to avoid the scenario where Cache A sees that VM is in state 2, shrinks its usage, VM enters state 0, Cache B sees this and grows its usage, VM enters state 2, repeat. I could imagine something similar being useful to userland as well, so that e.g. databases know whether they should keep more deserialized pages in RAM or free them and hand back memory (at the expense of doing more CPU work the next time those pages are needed). -- Colin Percival FreeBSD Release Engineering Lead & EC2 platform maintainer Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid