From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755203AbcEXPMu (ORCPT ); Tue, 24 May 2016 11:12:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45601 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751969AbcEXPMs (ORCPT ); Tue, 24 May 2016 11:12:48 -0400 Date: Tue, 24 May 2016 18:12:43 +0300 From: "Michael S. Tsirkin" To: "Li, Liang Z" Cc: "linux-kernel@vger.kernel.org" , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" , "akpm@linux-foundation.org" , "pbonzini@redhat.com" , "dgilbert@redhat.com" , "amit.shah@redhat.com" , "kvm@vger.kernel.org" Subject: Re: [PATCH RFC kernel] balloon: speed up inflating/deflating process Message-ID: <20160524181054-mutt-send-email-mst@redhat.com> References: <1463738386-30868-1-git-send-email-liang.z.li@intel.com> <20160520120038.GA28757@redhat.com> <20160524130041-mutt-send-email-mst@redhat.com> <20160524111135.GA7392@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 24 May 2016 15:12:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 24, 2016 at 02:36:08PM +0000, Li, Liang Z wrote: > > > > > > This can be pre-initialized, correct? > > > > > > > > > > pre-initialized? I am not quite understand your mean. > > > > > > > > I think you can maintain sg as part of device state and init sg with the > > bitmap. > > > > > > > > > > I got it. > > > > > > > > > This is grossly inefficient if you only requested a single page. > > > > > > And it's also allocating memory very aggressively without ever > > > > > > telling the host what is going on. > > > > > > > > > > If only requested a single page, there is no need to send the > > > > > entire page bitmap, This RFC patch has already considered about this. > > > > > > > > where's that addressed in code? > > > > > > > > > > By record the start_pfn and end_pfn. > > > > > > The start_pfn & end_pfn will be updated in set_page_bitmap() and will > > > be used in the function tell_host(): > > > > > > ---------------------------------------------------------------------- > > > ----------- > > > +static void set_page_bitmap(struct virtio_balloon *vb, struct page > > > +*page) { > > > + unsigned int i; > > > + unsigned long *bitmap = vb->page_bitmap; > > > + unsigned long balloon_pfn = page_to_balloon_pfn(page); > > > + > > > + for (i = 0; i < VIRTIO_BALLOON_PAGES_PER_PAGE; i++) > > > + set_bit(balloon_pfn + i, bitmap); > > > > BTW, there's a page size value in header so there is no longer need to set > > multiple bits per page. > > Yes, you are right. > > > > > > + if (balloon_pfn < vb->start_pfn) > > > + vb->start_pfn = balloon_pfn; > > > + if (balloon_pfn > vb->end_pfn) > > > + vb->end_pfn = balloon_pfn; > > > +} > > > > Sounds good, but you also need to limit by allocated bitmap size. > > Why should we limit the page bitmap size? Is it no good to send a large page bitmap? > or to save the memory used for page bitmap? Or some other reason? To save memory. First allocating a large bitmap can fail, second this is pinned memory that is wasted - it's unused most of the time while guest is running. > > > > > > > > + unsigned long start_pfn, end_pfn, flags = 0, bmap_len; > > > + struct scatterlist sg[5]; > > > + > > > + start_pfn = rounddown(vb->start_pfn, BITS_PER_LONG); > > > + end_pfn = roundup(vb->end_pfn, BITS_PER_LONG); > > > + bmap_len = (end_pfn - start_pfn) / BITS_PER_LONG * > > sizeof(long); > > > + > > > + sg_init_table(sg, 5); > > > + sg_set_buf(&sg[0], &flags, sizeof(flags)); > > > + sg_set_buf(&sg[1], &start_pfn, sizeof(start_pfn)); > > > + sg_set_buf(&sg[2], &page_shift, sizeof(page_shift)); > > > + sg_set_buf(&sg[3], &bmap_len, sizeof(bmap_len)); > > > + sg_set_buf(&sg[4], vb->page_bitmap + > > > + (start_pfn / BITS_PER_LONG), bmap_len); > > > > Looks wrong. start_pfn should start at offset 0 I think ... > > I don't know what is wrong here, could you tell me why? > > Thanks! > > Liang start_pfn should mean "bit 0 in bitmap refers to pfn X". So it does not make sense to also add it as offset within bitmap. -- MST