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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67474C433EF for ; Mon, 20 Jun 2022 07:32:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239384AbiFTHc3 (ORCPT ); Mon, 20 Jun 2022 03:32:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35140 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236876AbiFTHcT (ORCPT ); Mon, 20 Jun 2022 03:32:19 -0400 Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9AA0DED6 for ; Mon, 20 Jun 2022 00:32:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1655710338; x=1687246338; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=+G28GLDrdNJ98I4YnokMT1hGC4CArBlW7m+z/O+dMU4=; b=lEpT+8QwSnh7czWAb+Jmokubqa8CRDubtV6YdIzaPZKIlUmTQxr4BFS+ /7wb+cwKWpNliTdRCELGXC0jdIP+2Q9sOY8542lPvEQMVsvgjTnEzsj70 0NcPmvJgQZhtRpYSdL0Mr7LxlocFy7m00HaqaxJzkP1vl7Do0qv3ydDPa stfXE428Mv/Xd+sFfTfftR5W06EnFVDGCY7dMYc1bKVL5/aAM7GNppl1k czhmj9RIxtuAwDl8nRjvXyWvZPy915LLsM2ZSCrmeSQ41vCIosfNHCCon ENoHY9y4quZ+8SWVNQuwGO6qzUYSWAmpyCrHqsEzW6cTkAMJPJA2maV3G w==; X-IronPort-AV: E=McAfee;i="6400,9594,10380"; a="278600784" X-IronPort-AV: E=Sophos;i="5.92,306,1650956400"; d="scan'208";a="278600784" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jun 2022 00:32:18 -0700 X-IronPort-AV: E=Sophos;i="5.92,306,1650956400"; d="scan'208";a="832989989" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.239.13.94]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jun 2022 00:32:17 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , Subject: Re: [PATCH v2 1/3] mm/swapfile: make security_vm_enough_memory_mm() work as expected References: <20220608144031.829-1-linmiaohe@huawei.com> <20220608144031.829-2-linmiaohe@huawei.com> Date: Mon, 20 Jun 2022 15:31:46 +0800 In-Reply-To: <20220608144031.829-2-linmiaohe@huawei.com> (Miaohe Lin's message of "Wed, 8 Jun 2022 22:40:29 +0800") Message-ID: <87r13jrdst.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Miaohe Lin writes: > security_vm_enough_memory_mm() checks whether a process has enough memory > to allocate a new virtual mapping. And total_swap_pages is considered as > available memory while swapoff tries to make sure there's enough memory > that can hold the swapped out memory. But total_swap_pages contains the > swap space that is being swapoff. So security_vm_enough_memory_mm() will > success even if there's no memory to hold the swapped out memory because > total_swap_pages always greater than or equal to p->pages. Per my understanding, swapoff will not allocate virtual mapping by itself. But after swapoff, the overcommit limit could be exceeded. security_vm_enough_memory_mm() is used to check that. For example, in a system with 4GB memory and 8GB swap, and 10GB is in use, CommitLimit: 4+8 = 12GB Committed_AS: 10GB security_vm_enough_memory_mm() in swapoff() will fail because 10+8 = 18 > 12. This is expected because after swapoff, the overcommit limit will be exceeded. If 3GB is in use, CommitLimit: 4+8 = 12GB Committed_AS: 3GB security_vm_enough_memory_mm() in swapoff() will succeed because 3+8 = 11 < 12. This is expected because after swapoff, the overcommit limit will not be exceeded. So, what's the real problem of the original implementation? Can you show it with an example as above? Best Regards, Huang, Ying > In order to fix it, p->pages should be retracted from total_swap_pages > first and then check whether there's enough memory for inuse swap pages. > > Signed-off-by: Miaohe Lin [snip]