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Subject: Re: [PATCH v9 5/5] virtio-balloon: VIRTIO_BALLOON_F_MISC_VQ
On 04/14/2017 01:08 AM, Michael S. Tsirkin wrote:
On Thu, Apr 13, 2017 at 05:35:08PM +0800, Wei Wang wrote:Add a new vq, miscq, to handle miscellaneous requests between the device and the driver. This patch implemnts the VIRTIO_BALLOON_MISCQ_INQUIRE_UNUSED_PAGESimplementsrequest sent from the device.Commands are sent from host and handled on guest. In fact how is this so different from stats? How about reusing the stats vq then? You can use one buffer for stats and one buffer for commands.
The meaning of the two vqs is a little different. statq is used for reporting statistics, while miscq is intended to be used to handle miscellaneous requests from the guest or host (I think it can also be used the other way around in the future when other new features are added which need the guest to send requests and the host to provide responses). I would prefer to have them separate, because: If we plan to combine them, we need to put the previous statq related implementation under miscq with a new command (I think we can't combine them without using commands to distinguish the two features). In this way, an old driver won't work with a new QEMU or a new driver won't work with an old QEMU. Would this be considered as an issue here?
+ miscq_out_hdr->flags = 0; + + for_each_populated_zone(zone) { + for (order = MAX_ORDER - 1; order > 0; order--) { + for (migratetype = 0; migratetype < MIGRATE_TYPES; + migratetype++) { + do { + ret = inquire_unused_page_block(zone, + order, migratetype, &page); + if (!ret) { + pfn = (u64)page_to_pfn(page); + add_one_chunk(vb, vq, + PAGE_CHUNK_TYPE_UNUSED, + pfn, + (u64)(1 << order)); + } + } while (!ret); + } + } + } + miscq_out_hdr->flags |= VIRTIO_BALLOON_MISCQ_F_COMPLETE;And where is miscq_out_hdr used? I see no add_outbuf anywhere. Things like this should be passed through function parameters and not stuffed into device structure, fields should be initialized before use and not where we happen to have the data handy.
miscq_out_hdr is linear with the payload (i.e. kmalloc(hdr+payload) ). It is the same as the use of statq - one request in-flight each time.
Also, _F_ is normally a bit number, you use it as a value here.
It intends to be a bit number. Bit 0 of flags to indicate the completion of handling the request.
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