[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG

From: Wei Wang
Subject: Re: [Qemu-devel] [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG
Date: Sat, 04 Nov 2017 19:09:23 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

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)
+ 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 
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)
-               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);

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?


reply via email to

[Prev in Thread] Current Thread [Next in Thread]