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Subject: Re: [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG
On 11/03/2017 07:25 PM, Tetsuo Handa wrote:
Wei Wang wrote:@@ -164,6 +284,8 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) break; }+ if (use_sg && xb_set_page(vb, page, &pfn_min, &pfn_max) < 0)Isn't this leaking "page" ?
Right, thanks, will add __free_page(page) here.
@@ -184,8 +307,12 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)num_allocated_pages = vb->num_pfns;/* Did we get any? */ - if (vb->num_pfns != 0) - tell_host(vb, vb->inflate_vq); + if (vb->num_pfns) { + if (use_sg) + tell_host_sgs(vb, vb->inflate_vq, pfn_min, pfn_max);Please describe why tell_host_sgs() can work without __GFP_DIRECT_RECLAIM allocation, for tell_host_sgs() is called with vb->balloon_lock mutex held.
Essentially, tell_host_sgs()-->send_balloon_page_sg()-->add_one_sg()-->virtqueue_add_inbuf( , , num=1 ,,GFP_KERNEL) won't need any memory allocation, because we always add one sg (i.e. num=1) each time. That memory allocation option is only used when multiple sgs are added (i.e. num > 1) and the implementation inside virtqueue_add_inbuf
need allocation of indirect descriptor table.We could also add some comments above the function to explain a little about this if necessary.
@@ -223,7 +353,13 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) page = balloon_page_dequeue(vb_dev_info); if (!page) break; - set_page_pfns(vb, vb->pfns + vb->num_pfns, page); + if (use_sg) { + if (xb_set_page(vb, page, &pfn_min, &pfn_max) < 0)Isn't this leaking "page" ?
Yes, will make it: if (xb_set_page(vb, page, &pfn_min, &pfn_max) < 0) { balloon_page_enqueue(..., page); break; }
If this is inside vb->balloon_lock mutex (isn't this?), xb_set_page() must not use __GFP_DIRECT_RECLAIM allocation, for leak_balloon_sg_oom() will be blocked on vb->balloon_lock mutex.
OK. Since the preload() doesn't need too much memory (< 4K in total), how about GFP_NOWAIT here?
Best, Wei
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