From owner-freebsd-hackers@freebsd.org Thu Sep 19 06:12:27 2019 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 2AE02F7670 for ; Thu, 19 Sep 2019 06:12:27 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 46Ymj61ycmz4JBg for ; Thu, 19 Sep 2019 06:12:25 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id x8J6CHNR072942 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Thu, 19 Sep 2019 09:12:20 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua x8J6CHNR072942 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id x8J6CGIZ072941; Thu, 19 Sep 2019 09:12:16 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Thu, 19 Sep 2019 09:12:16 +0300 From: Konstantin Belousov To: Yoshihiro Ota Cc: freebsd-hackers@freebsd.org Subject: Re: How to access user process memory/pages from swap_pager.c Message-ID: <20190919061216.GG2559@kib.kiev.ua> References: <20190919003419.007b6de7f9887617f254e334@j.email.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190919003419.007b6de7f9887617f254e334@j.email.ne.jp> User-Agent: Mutt/1.12.1 (2019-06-15) X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on tom.home X-Rspamd-Queue-Id: 46Ymj61ycmz4JBg X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-2.00 / 15.00]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; R_SPF_SOFTFAIL(0.00)[~all]; IP_SCORE_FREEMAIL(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; IP_SCORE(0.00)[ip: (-2.63), ipnet: 2001:470::/32(-4.47), asn: 6939(-3.23), country: US(-0.05)]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; RCVD_COUNT_TWO(0.00)[2]; FREEMAIL_ENVFROM(0.00)[gmail.com]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 Sep 2019 06:12:27 -0000 On Thu, Sep 19, 2019 at 12:34:19AM -0400, Yoshihiro Ota wrote: > Hi, > > I'm trying to get some data / statistics for pages being swapped out. > > I'm trying to access pages being swapped out in swp_pager_putpages. > Given I have access to vm_page_t, it looked like I would be able to use VM_PAGE_TO_PHYS() to access user pages. > > However, I get page-fault panics like: > panic: vm_fault_hold: fault on nofault entry, addr: 0 > > Which functions/setup do I need to access/copy user data being swapped? I am not sure what you are trying to do, but whatever is it, it is unreasonable. When a page is swapped out, its physical memory frame, described by vm_page_t, is reused for something else. The only resource consumed by swapped out page is the index in the vm_object page queue, swap space which holds the actual content, and pointer from swap pager data to the swap location.