From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5A600C36008 for ; Wed, 26 Mar 2025 16:18:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: Message-ID:Date:References:In-Reply-To:Subject:Cc:To:From:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=cryOLtlUv/wnK3wghrxUGzQFVc+vixpm5OncZRYmfY0=; b=bnDFA1FjnMTANOSmaN2S9Mscea YM3U6KiGp3jwRLH+reDIIhv+pDlAAkYOlfuCz6bgmXWbe4xWp/QD7WG1ZV9i4jqQdEXy/W28e/TSz 9ZYNGyTmf27a0zHz2jLUUgCKNdSr1unoYgYq1ixgOfKwewXS7/P1+og32mttlJwFjHDtiQOFEfMsi ONto7uQHEEB9nJxrdyg/+99EdvH3ymvEY+LT6dwun12SBfASjFxk5Bzusoyo8n65ED/O2kOiezwTA ffA47VRTdoXtbezhSEI45UDVz6frucJXED7e2Mjq0BzV9V4+dH5G16NNrYIpB5k41ovhxKlILp4YA 0+w1NwEQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1txTSh-00000008zmz-0vLc; Wed, 26 Mar 2025 16:18:39 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.1 #2 (Red Hat Linux)) id 1txTSd-00000008zmq-3G5f for kexec@lists.infradead.org; Wed, 26 Mar 2025 16:18:35 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 2A6946115A; Wed, 26 Mar 2025 16:18:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CCB3C4CEE2; Wed, 26 Mar 2025 16:18:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1743005913; bh=62UK7sgqLy7YlWGLIBWH0rQyGMv0oNWe5Wt7OkG2t2o=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=LdR103iIgMle3veCG5V4CzGebSd89g32/pXSAVfRo0VtzYkq549g6URwrOkAOoMTp ZNz9gVD6klRNX6tPCqdnyua9NDkzPvB5i5TX7icqz62+gERX61O5MwWASeAokKPmSg IBoKfCRXBjo6J3bIdmWdI/ng4e05Y04Pa/auc91ohtFbQR8WjixNnuH21lmrX05eig 8ZlDmEoIvsFD1gf0ksYdPaBa3g8DdAQ3J8swuXuls1/BaC6DPxcB7iecUNO0ZHwccO pJNCcu832sqa5MuG7poxR/cUHswABVzUPNiRRoCcbyesdTSbL/69UEjph0YWiw58OX YAF2ZRD++0lrQ== From: Pratyush Yadav To: Jason Gunthorpe Cc: Pratyush Yadav , David Rientjes , Alexander Graf , Anthony Yznaga , Dave Hansen , David Hildenbrand , Frank van der Linden , James Gowans , Junaid Shahid , Matthew Wilcox , Mike Rapoport , Pankaj Gupta , Pasha Tatashin , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" , linux-mm@kvack.org, kexec@lists.infradead.org Subject: Re: [Hypervisor Live Update] Notes from March 10, 2025 In-Reply-To: <20250320122303.GT9311@nvidia.com> References: <20250317172255.GO9311@nvidia.com> <755e80a2-60a7-4a04-9eb2-714e89ea34c5@app.fastmail.com> <20250320122303.GT9311@nvidia.com> Date: Wed, 26 Mar 2025 16:18:29 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Thu, Mar 20 2025, Jason Gunthorpe wrote: >> I didn't mean the exact flags value, but the ability to have >> per-folio flags. The exact bits and their meaning would of course >> need to be part of the ABI. Shmem uses the dirty and uptodate flags >> to track some state on the folios, and the flags can affect it's >> behavior (lazily zeroing out falloc-ed pages for example). I am >> assuming other FD types or drivers might also want to store >> per-folio information. Having KHO core provide this facility can >> avoid duplicating the logic in each subsystem. > > For something simple like shmem I'd probably just suggest a side car bitmap > array or something? > > The trouble with trying to feed flags through the xarray thing is that > the memory holding that pfn data across the kexec is not itself > preserved memory so it is all blown away once the allocator starts. > > Any data that needs to be preserved further has to be copied into the > frozen struct page, which is pretty limiting in terms of what you > could preserve. A few bits could maybe work out but not alot of data. Right, that makes sense. I can live with a sidecar bitmap then. [...] -- Regards, Pratyush Yadav