From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id EBFE26B0003 for ; Thu, 1 Feb 2018 14:14:40 -0500 (EST) Received: by mail-io0-f199.google.com with SMTP id e69so18551428iod.17 for ; Thu, 01 Feb 2018 11:14:40 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id e84si170927iof.173.2018.02.01.11.14.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Feb 2018 11:14:39 -0800 (PST) Date: Thu, 1 Feb 2018 21:14:25 +0200 From: "Michael S. Tsirkin" Subject: Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Message-ID: <20180201211114-mutt-send-email-mst@kernel.org> References: <1516790562-37889-1-git-send-email-wei.w.wang@intel.com> <1516790562-37889-3-git-send-email-wei.w.wang@intel.com> <20180124183349-mutt-send-email-mst@kernel.org> <5A694FB5.5090803@intel.com> <17068749-d2c7-61bb-4637-a1aee5a0d0fb@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <17068749-d2c7-61bb-4637-a1aee5a0d0fb@I-love.SAKURA.ne.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: Wei Wang , virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org, pbonzini@redhat.com, liliang.opensource@gmail.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com, riel@redhat.com On Thu, Jan 25, 2018 at 08:28:52PM +0900, Tetsuo Handa wrote: > On 2018/01/25 12:32, Wei Wang wrote: > > On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote: > >> On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote: > >> + > >> +static void report_free_page_func(struct work_struct *work) > >> +{ > >> + struct virtio_balloon *vb; > >> + unsigned long flags; > >> + > >> + vb = container_of(work, struct virtio_balloon, report_free_page_work); > >> + > >> + /* Start by sending the obtained cmd id to the host with an outbuf */ > >> + send_cmd_id(vb, &vb->start_cmd_id); > >> + > >> + /* > >> + * Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to > >> + * indicate a new request can be queued. > >> + */ > >> + spin_lock_irqsave(&vb->stop_update_lock, flags); > >> + vb->start_cmd_id = cpu_to_virtio32(vb->vdev, > >> + VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID); > >> + spin_unlock_irqrestore(&vb->stop_update_lock, flags); > >> + > >> + walk_free_mem_block(vb, 0, &virtio_balloon_send_free_pages); > >> Can you teach walk_free_mem_block to return the && of all > >> return calls, so caller knows whether it completed? > > > > There will be two cases that can cause walk_free_mem_block to return without completing: > > 1) host requests to stop in advance > > 2) vq->broken > > > > How about letting walk_free_mem_block simply return the value returned by its callback (i.e. virtio_balloon_send_free_pages)? > > > > For host requests to stop, it returns "1", and the above only bails out when walk_free_mem_block return a "< 0" value. > > I feel that virtio_balloon_send_free_pages is doing too heavy things. > > It can be called for many times with IRQ disabled. Number of times > it is called depends on amount of free pages (and fragmentation state). > Generally, more free pages, more calls. > > Then, why don't you allocate some pages for holding all pfn values > and then call walk_free_mem_block() only for storing pfn values > and then send pfn values without disabling IRQ? So going over it, at some level we are talking about optimizations here. I'll go over it one last time but at some level we might be able to make progress faster if we start by enabling the functionality in question. If there are no other issues, I'm inclined to merge. If nothing else, this will make it possible for people to experiment and report sources of overhead. -- MST -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org