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[67.71.176.35]) by smtp.gmail.com with ESMTPSA id u8sm7720647qkj.9.2020.08.23.12.16.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 23 Aug 2020 12:16:17 -0700 (PDT) Sender: Mark Johnston Date: Sun, 23 Aug 2020 15:16:14 -0400 From: Mark Johnston To: Ian Lepore Cc: guyvert@secmail.pro, freebsd-hackers@freebsd.org Subject: Re: Running BSD from RAM memory using zroot Message-ID: <20200823191614.GD1954@raichu> References: <6a7da06949dbd8f1c38d5faa22f3f28b.squirrel@giyzk7o6dcunb2ry.onion> <6e395923c808ccc34f5f88efffd7853baef1d3ec.camel@freebsd.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e395923c808ccc34f5f88efffd7853baef1d3ec.camel@freebsd.org> X-Rspamd-Queue-Id: 4BZQ3675l1z40cJ X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=JfRmrBW9; dmarc=none; spf=pass (mx1.freebsd.org: domain of markjdb@gmail.com designates 2607:f8b0:4864:20::831 as permitted sender) smtp.mailfrom=markjdb@gmail.com X-Spamd-Result: default: False [0.05 / 15.00]; FROM_NEQ_ENVFROM(0.00)[markj@freebsd.org,markjdb@gmail.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; TO_DN_SOME(0.00)[]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; MIME_GOOD(-0.10)[text/plain]; MID_RHS_NOT_FQDN(0.50)[]; DMARC_NA(0.00)[freebsd.org]; RCVD_COUNT_THREE(0.00)[3]; TO_MATCH_ENVRCPT_SOME(0.00)[]; DKIM_TRACE(0.00)[gmail.com:+]; NEURAL_HAM_SHORT(-0.25)[-0.247]; RCVD_IN_DNSWL_NONE(0.00)[2607:f8b0:4864:20::831:from]; FORGED_SENDER(0.30)[markj@freebsd.org,markjdb@gmail.com]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; RCVD_TLS_ALL(0.00)[]; MAILMAN_DEST(0.00)[freebsd-hackers] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 23 Aug 2020 19:16:20 -0000 On Sun, Aug 23, 2020 at 12:26:07PM -0600, Ian Lepore wrote: > Note that deleting md0 will not necessarily > make the memory it was using available for further use. The memory > will be in the form of a preloaded module, and it's not clear to me > that it can be unloaded (but I'm also not sure that it can't be). On i386 and amd64 preloaded memory can be freed, see kmem_bootstrap_free(). On other platforms it is leaked. It is not too hard to fix for a given platform, the pmap needs to ensure that pages containing preloaded data and the page table pages mapping preloaded data are initialized properly. See r336505 for an example.