From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752763AbdLQKVk (ORCPT ); Sun, 17 Dec 2017 05:21:40 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:18255 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751291AbdLQKVh (ORCPT ); Sun, 17 Dec 2017 05:21:37 -0500 To: wei.w.wang@intel.com, willy@infradead.org Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com, mhocko@kernel.org, akpm@linux-foundation.org, mawilcox@microsoft.com, david@redhat.com, cornelia.huck@de.ibm.com, mgorman@techsingularity.net, aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu@aliyun.com, nilal@redhat.com, riel@redhat.com Subject: Re: [PATCH v19 3/7] xbitmap: add more operations From: Tetsuo Handa References: <1513079759-14169-4-git-send-email-wei.w.wang@intel.com> <20171215184256.GA27160@bombadil.infradead.org> <5A34F193.5040700@intel.com> <201712162028.FEB87079.FOJFMQHVOSLtFO@I-love.SAKURA.ne.jp> <5A35FF89.8040500@intel.com> In-Reply-To: <5A35FF89.8040500@intel.com> Message-Id: <201712171921.IBB30790.VOOOFMQHFSLFJt@I-love.SAKURA.ne.jp> X-Mailer: Winbiff [Version 2.51 PL2] X-Accept-Language: ja,en,zh Date: Sun, 17 Dec 2017 19:21:35 +0900 Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wei Wang wrote: > > But passing GFP_NOWAIT means that we can handle allocation failure. There is > > no need to use preload approach when we can handle allocation failure. > > I think the reason we need xb_preload is because radix tree insertion > needs the memory being preallocated already (it couldn't suffer from > memory failure during the process of inserting, probably because > handling the failure there isn't easy, Matthew may know the backstory of > this) According to https://lwn.net/Articles/175432/ , I think that preloading is needed only when failure to insert an item into a radix tree is a significant problem. That is, when failure to insert an item into a radix tree is not a problem, I think that we don't need to use preloading. > > So, I think we can handle the memory failure with xb_preload, which > stops going into the radix tree APIs, but shouldn't call radix tree APIs > without the related memory preallocated. It seems to me that virtio-ballon case has no problem without using preloading.