Messages in this thread Patch in this message | | | Date | Sat, 04 Nov 2017 19:09:23 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG |
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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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