lkml.org 
[lkml]   [2016]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page info
From
Date
On 11/30/2016 12:43 AM, Liang Li wrote:
> +static void send_unused_pages_info(struct virtio_balloon *vb,
> + unsigned long req_id)
> +{
> + struct scatterlist sg_in;
> + unsigned long pos = 0;
> + struct virtqueue *vq = vb->req_vq;
> + struct virtio_balloon_resp_hdr *hdr = vb->resp_hdr;
> + int ret, order;
> +
> + mutex_lock(&vb->balloon_lock);
> +
> + for (order = MAX_ORDER - 1; order >= 0; order--) {

I scratched my head for a bit on this one. Why are you walking over
orders, *then* zones. I *think* you're doing it because you can
efficiently fill the bitmaps at a given order for all zones, then move
to a new bitmap. But, it would be interesting to document this.

> + pos = 0;
> + ret = get_unused_pages(vb->resp_data,
> + vb->resp_buf_size / sizeof(unsigned long),
> + order, &pos);

FWIW, get_unsued_pages() is a pretty bad name. "get" usually implies
bumping reference counts or consuming something. You're just
"recording" or "marking" them.

> + if (ret == -ENOSPC) {
> + void *new_resp_data;
> +
> + new_resp_data = kmalloc(2 * vb->resp_buf_size,
> + GFP_KERNEL);
> + if (new_resp_data) {
> + kfree(vb->resp_data);
> + vb->resp_data = new_resp_data;
> + vb->resp_buf_size *= 2;

What happens to the data in ->resp_data at this point? Doesn't this
just throw it away?

...
> +struct page_info_item {
> + __le64 start_pfn : 52; /* start pfn for the bitmap */
> + __le64 page_shift : 6; /* page shift width, in bytes */
> + __le64 bmap_len : 6; /* bitmap length, in bytes */
> +};

Is 'bmap_len' too short? a 64-byte buffer is a bit tiny. Right?

> +static int mark_unused_pages(struct zone *zone,
> + unsigned long *unused_pages, unsigned long size,
> + int order, unsigned long *pos)
> +{
> + unsigned long pfn, flags;
> + unsigned int t;
> + struct list_head *curr;
> + struct page_info_item *info;
> +
> + if (zone_is_empty(zone))
> + return 0;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> +
> + if (*pos + zone->free_area[order].nr_free > size)
> + return -ENOSPC;

Urg, so this won't partially fill? So, what the nr_free pages limit
where we no longer fit in the kmalloc()'d buffer where this simply won't
work?

> + for (t = 0; t < MIGRATE_TYPES; t++) {
> + list_for_each(curr, &zone->free_area[order].free_list[t]) {
> + pfn = page_to_pfn(list_entry(curr, struct page, lru));
> + info = (struct page_info_item *)(unused_pages + *pos);
> + info->start_pfn = pfn;
> + info->page_shift = order + PAGE_SHIFT;
> + *pos += 1;
> + }
> + }

Do we need to fill in ->bmap_len here?

\
 
 \ /
  Last update: 2016-11-30 20:18    [W:0.082 / U:0.240 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site