From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752741Ab1DGKXK (ORCPT ); Thu, 7 Apr 2011 06:23:10 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:56943 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751576Ab1DGKXI convert rfc822-to-8bit (ORCPT ); Thu, 7 Apr 2011 06:23:08 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=ZgsrDlb70YEfEAg5XGba9Gici9kf99W7X0iKfq2Zn/MCFgPHAisqGtqy2p9GTThtv0 CpNJxB+2fZ+P7fWUxlQgaum5ferwgKRAMTwbv8RkgSKVmhSBLUr8LfVlkvhSzK/C0Drb HNF4o79wNU8gTkD+QXO7B5oXRWlfpi+fYeiM0= MIME-Version: 1.0 In-Reply-To: <20110407095646.GA30788@aepfle.de> References: <20110407095646.GA30788@aepfle.de> Date: Thu, 7 Apr 2011 18:23:07 +0800 Message-ID: Subject: Re: dynamic oldmem in kdump kernel From: =?UTF-8?Q?Am=C3=A9rico_Wang?= To: Olaf Hering Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 7, 2011 at 5:56 PM, Olaf Hering wrote: > > Recently kdump for pv-on-hvm Xen guests was implemented by me. > > One issue remains: > The xen_balloon driver in the guest frees guest pages and gives them > back to the hypervisor. These pages are marked as mmio in the > hypervisor. During a read of such a page via the /proc/vmcore interface > the hypervisor calls the qemu-dm process. qemu-dm tries to map the page, > this attempt fails because the page is not backed by ram and 0xff is > returned. All this generates high load in dom0 because the reads come > as 8byte requests. > > There seems to be no way to make the crash kernel aware of the state of > individual pages in the crashed kernel, it is not aware of memory > ballooning. And doing that from within the "kernel to crash" seems error > prone. Since over time the fragmentation will increase, it would be best > if the crash kernel itself queries the state of oldmem pages. > > If copy_oldmem_page() would call a function, a hook, provided by the Xen > pv-on-hvm drivers to query if the pfn to read from is really backed by > ram the load issue could be avoided. Unfortunately, even Xen needs to > get a new interface to query the state of individual hvm guest pfns for > the purpose mentioned above. This makes sense for me, we might need a Xen-specific copy_oldmem_page() hook and a native hook. > > Another issue, slightly related, is memory hotplug. > How is this currently handled for kdump?  Is there code which > automatically reconfigures the kdump kernel with the new memory ranges? > No, the crashkernel memory is reserved during boot, and it is static after that (except you can shrink this memory via /sys). Kdump isn't aware of memory hotplug. Thanks. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pw0-f49.google.com ([209.85.160.49]) by canuck.infradead.org with esmtps (Exim 4.72 #1 (Red Hat Linux)) id 1Q7mMp-00063V-55 for kexec@lists.infradead.org; Thu, 07 Apr 2011 10:23:15 +0000 Received: by pwi8 with SMTP id 8so1080442pwi.36 for ; Thu, 07 Apr 2011 03:23:08 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110407095646.GA30788@aepfle.de> References: <20110407095646.GA30788@aepfle.de> Date: Thu, 7 Apr 2011 18:23:07 +0800 Message-ID: Subject: Re: dynamic oldmem in kdump kernel From: =?UTF-8?Q?Am=C3=A9rico_Wang?= List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: kexec-bounces@lists.infradead.org Errors-To: kexec-bounces+dwmw2=twosheds.infradead.org@lists.infradead.org To: Olaf Hering Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org T24gVGh1LCBBcHIgNywgMjAxMSBhdCA1OjU2IFBNLCBPbGFmIEhlcmluZyA8b2xhZkBhZXBmbGUu ZGU+IHdyb3RlOgo+Cj4gUmVjZW50bHkga2R1bXAgZm9yIHB2LW9uLWh2bSBYZW4gZ3Vlc3RzIHdh cyBpbXBsZW1lbnRlZCBieSBtZS4KPgo+IE9uZSBpc3N1ZSByZW1haW5zOgo+IFRoZSB4ZW5fYmFs bG9vbiBkcml2ZXIgaW4gdGhlIGd1ZXN0IGZyZWVzIGd1ZXN0IHBhZ2VzIGFuZCBnaXZlcyB0aGVt Cj4gYmFjayB0byB0aGUgaHlwZXJ2aXNvci4gVGhlc2UgcGFnZXMgYXJlIG1hcmtlZCBhcyBtbWlv IGluIHRoZQo+IGh5cGVydmlzb3IuIER1cmluZyBhIHJlYWQgb2Ygc3VjaCBhIHBhZ2UgdmlhIHRo ZSAvcHJvYy92bWNvcmUgaW50ZXJmYWNlCj4gdGhlIGh5cGVydmlzb3IgY2FsbHMgdGhlIHFlbXUt ZG0gcHJvY2Vzcy4gcWVtdS1kbSB0cmllcyB0byBtYXAgdGhlIHBhZ2UsCj4gdGhpcyBhdHRlbXB0 IGZhaWxzIGJlY2F1c2UgdGhlIHBhZ2UgaXMgbm90IGJhY2tlZCBieSByYW0gYW5kIDB4ZmYgaXMK PiByZXR1cm5lZC4gQWxsIHRoaXMgZ2VuZXJhdGVzIGhpZ2ggbG9hZCBpbiBkb20wIGJlY2F1c2Ug dGhlIHJlYWRzIGNvbWUKPiBhcyA4Ynl0ZSByZXF1ZXN0cy4KPgo+IFRoZXJlIHNlZW1zIHRvIGJl IG5vIHdheSB0byBtYWtlIHRoZSBjcmFzaCBrZXJuZWwgYXdhcmUgb2YgdGhlIHN0YXRlIG9mCj4g aW5kaXZpZHVhbCBwYWdlcyBpbiB0aGUgY3Jhc2hlZCBrZXJuZWwsIGl0IGlzIG5vdCBhd2FyZSBv ZiBtZW1vcnkKPiBiYWxsb29uaW5nLiBBbmQgZG9pbmcgdGhhdCBmcm9tIHdpdGhpbiB0aGUgImtl cm5lbCB0byBjcmFzaCIgc2VlbXMgZXJyb3IKPiBwcm9uZS4gU2luY2Ugb3ZlciB0aW1lIHRoZSBm cmFnbWVudGF0aW9uIHdpbGwgaW5jcmVhc2UsIGl0IHdvdWxkIGJlIGJlc3QKPiBpZiB0aGUgY3Jh c2gga2VybmVsIGl0c2VsZiBxdWVyaWVzIHRoZSBzdGF0ZSBvZiBvbGRtZW0gcGFnZXMuCj4KPiBJ ZiBjb3B5X29sZG1lbV9wYWdlKCkgd291bGQgY2FsbCBhIGZ1bmN0aW9uLCBhIGhvb2ssIHByb3Zp ZGVkIGJ5IHRoZSBYZW4KPiBwdi1vbi1odm0gZHJpdmVycyB0byBxdWVyeSBpZiB0aGUgcGZuIHRv IHJlYWQgZnJvbSBpcyByZWFsbHkgYmFja2VkIGJ5Cj4gcmFtIHRoZSBsb2FkIGlzc3VlIGNvdWxk IGJlIGF2b2lkZWQuIFVuZm9ydHVuYXRlbHksIGV2ZW4gWGVuIG5lZWRzIHRvCj4gZ2V0IGEgbmV3 IGludGVyZmFjZSB0byBxdWVyeSB0aGUgc3RhdGUgb2YgaW5kaXZpZHVhbCBodm0gZ3Vlc3QgcGZu cyBmb3IKPiB0aGUgcHVycG9zZSBtZW50aW9uZWQgYWJvdmUuCgpUaGlzIG1ha2VzIHNlbnNlIGZv ciBtZSwgd2UgbWlnaHQgbmVlZCBhIFhlbi1zcGVjaWZpYyBjb3B5X29sZG1lbV9wYWdlKCkKaG9v ayBhbmQgYSBuYXRpdmUgaG9vay4KCj4KPiBBbm90aGVyIGlzc3VlLCBzbGlnaHRseSByZWxhdGVk LCBpcyBtZW1vcnkgaG90cGx1Zy4KPiBIb3cgaXMgdGhpcyBjdXJyZW50bHkgaGFuZGxlZCBmb3Ig a2R1bXA/IMKgSXMgdGhlcmUgY29kZSB3aGljaAo+IGF1dG9tYXRpY2FsbHkgcmVjb25maWd1cmVz IHRoZSBrZHVtcCBrZXJuZWwgd2l0aCB0aGUgbmV3IG1lbW9yeSByYW5nZXM/Cj4KCk5vLCB0aGUg Y3Jhc2hrZXJuZWwgbWVtb3J5IGlzIHJlc2VydmVkIGR1cmluZyBib290LCBhbmQgaXQgaXMgc3Rh dGljIGFmdGVyCnRoYXQgKGV4Y2VwdCB5b3UgY2FuIHNocmluayB0aGlzIG1lbW9yeSB2aWEgL3N5 cykuIEtkdW1wIGlzbid0IGF3YXJlIG9mCm1lbW9yeSBob3RwbHVnLgoKVGhhbmtzLgoKX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18Ka2V4ZWMgbWFpbGluZyBs aXN0CmtleGVjQGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcv bWFpbG1hbi9saXN0aW5mby9rZXhlYwo=