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Re: [Qemu-devel] [PATCH v1 3/3] virtio-balloon: Rework pbp tracking data
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH v1 3/3] virtio-balloon: Rework pbp tracking data |
Date: |
Mon, 22 Jul 2019 13:04:36 +1000 |
User-agent: |
Mutt/1.12.0 (2019-05-25) |
On Fri, Jul 19, 2019 at 06:01:20PM +0200, David Hildenbrand wrote:
> Using the address of a RAMBlock to test for a matching pbp is not really
> safe. Instead, let's use the guest physical address of the base page
> along with the page size (via the number of subpages).
>
> While at it, move "struct PartiallyBalloonedPage" to virtio-balloon.h
> now (previously most probably avoided to te the ramblock), renaming it.
>
> Also, let's only dynamically allocating the bitmap. This makes the code
> easier to read and maintain - we can reuse bitmap_new().
>
> Signed-off-by: David Hildenbrand <address@hidden>
This mostly looks good, but one thing bothers me..
> ---
> hw/virtio/virtio-balloon.c | 52 +++++++++++++++++-------------
> include/hw/virtio/virtio-balloon.h | 15 +++++++--
> 2 files changed, 42 insertions(+), 25 deletions(-)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 29cee344b2..8e5f9459c2 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -34,23 +34,31 @@
>
> #define BALLOON_PAGE_SIZE (1 << VIRTIO_BALLOON_PFN_SHIFT)
>
> -struct PartiallyBalloonedPage {
> - RAMBlock *rb;
> - ram_addr_t base;
> - unsigned long bitmap[];
> -};
> -
> static void virtio_balloon_reset_pbp(VirtIOBalloon *balloon)
> {
> - g_free(balloon->pbp);
> - balloon->pbp = NULL;
> + balloon->pbp.base_gpa = 0;
> + balloon->pbp.subpages = 0;
> + g_free(balloon->pbp.bitmap);
> + balloon->pbp.bitmap = NULL;
> +}
> +
> +static bool virtio_balloon_pbp_valid(VirtIOBalloon *balloon)
> +{
> + return balloon->pbp.bitmap;
> +}
> +
> +static bool virtio_balloon_pbp_matches(VirtIOBalloon *balloon,
> + ram_addr_t base_gpa, long subpages)
> +{
> + return balloon->pbp.subpages == subpages &&
> + balloon->pbp.base_gpa == base_gpa;
.. so, I'm trying to think what base_gpa matching, but subpages not
matching means. I think that can only happen if a pbp is created,
then the ramblock it was in is unplugged, then another ramblock is
plugged in covering the same address and with a different (host) page
size. Which is unlikely but possible, IIUC. However, also possible
and marginally less unlikely is to plug a new block of the same page
size, in which case this *will* match, but presumably the pbp should
still be discarded.
> }
>
> static void balloon_inflate_page(VirtIOBalloon *balloon,
> MemoryRegion *mr, hwaddr mr_offset)
> {
> void *addr = memory_region_get_ram_ptr(mr) + mr_offset;
> - ram_addr_t rb_offset, rb_aligned_offset;
> + ram_addr_t rb_offset, rb_aligned_offset, base_gpa;
> RAMBlock *rb;
> size_t rb_page_size;
> int subpages;
> @@ -81,32 +89,32 @@ static void balloon_inflate_page(VirtIOBalloon *balloon,
>
> rb_aligned_offset = QEMU_ALIGN_DOWN(rb_offset, rb_page_size);
> subpages = rb_page_size / BALLOON_PAGE_SIZE;
> + base_gpa = memory_region_get_ram_addr(mr) + mr_offset -
> + (rb_offset - rb_aligned_offset);
>
> - if (balloon->pbp
> - && (rb != balloon->pbp->rb
> - || rb_aligned_offset != balloon->pbp->base)) {
> + if (virtio_balloon_pbp_valid(balloon) &&
> + !virtio_balloon_pbp_matches(balloon, base_gpa, subpages)) {
> /* We've partially ballooned part of a host page, but now
> * we're trying to balloon part of a different one. Too hard,
> * give up on the old partial page */
> virtio_balloon_reset_pbp(balloon);
> }
>
> - if (!balloon->pbp) {
> + if (!virtio_balloon_pbp_valid(balloon)) {
> /* Starting on a new host page */
> - size_t bitlen = BITS_TO_LONGS(subpages) * sizeof(unsigned long);
> - balloon->pbp = g_malloc0(sizeof(PartiallyBalloonedPage) + bitlen);
> - balloon->pbp->rb = rb;
> - balloon->pbp->base = rb_aligned_offset;
> + balloon->pbp.base_gpa = base_gpa;
> + balloon->pbp.subpages = subpages;
> + balloon->pbp.bitmap = bitmap_new(subpages);
> }
>
> - set_bit((rb_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
> - balloon->pbp->bitmap);
> + set_bit((rb_offset - rb_aligned_offset) / BALLOON_PAGE_SIZE,
> + balloon->pbp.bitmap);
>
> - if (bitmap_full(balloon->pbp->bitmap, subpages)) {
> + if (bitmap_full(balloon->pbp.bitmap, subpages)) {
> /* We've accumulated a full host page, we can actually discard
> * it now */
>
> - ram_block_discard_range(rb, balloon->pbp->base, rb_page_size);
> + ram_block_discard_range(rb, rb_aligned_offset, rb_page_size);
> /* We ignore errors from ram_block_discard_range(), because it
> * has already reported them, and failing to discard a balloon
> * page is not fatal */
> @@ -130,7 +138,7 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
> rb = qemu_ram_block_from_host(addr, false, &rb_offset);
> rb_page_size = qemu_ram_pagesize(rb);
>
> - if (balloon->pbp) {
> + if (virtio_balloon_pbp_valid(balloon)) {
> /* Let's play safe and always reset the pbp on deflation requests. */
> virtio_balloon_reset_pbp(balloon);
> }
> diff --git a/include/hw/virtio/virtio-balloon.h
> b/include/hw/virtio/virtio-balloon.h
> index 5a99293a45..0190d78d71 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -33,8 +33,6 @@ typedef struct virtio_balloon_stat_modern {
> uint64_t val;
> } VirtIOBalloonStatModern;
>
> -typedef struct PartiallyBalloonedPage PartiallyBalloonedPage;
> -
> enum virtio_balloon_free_page_report_status {
> FREE_PAGE_REPORT_S_STOP = 0,
> FREE_PAGE_REPORT_S_REQUESTED = 1,
> @@ -42,6 +40,12 @@ enum virtio_balloon_free_page_report_status {
> FREE_PAGE_REPORT_S_DONE = 3,
> };
>
> +typedef struct VirtIOPartiallyBalloonedPage {
> + ram_addr_t base_gpa;
> + long subpages;
> + unsigned long *bitmap;
> +} VirtIOPartiallyBalloonedPage;
> +
> typedef struct VirtIOBalloon {
> VirtIODevice parent_obj;
> VirtQueue *ivq, *dvq, *svq, *free_page_vq;
> @@ -70,7 +74,12 @@ typedef struct VirtIOBalloon {
> int64_t stats_last_update;
> int64_t stats_poll_interval;
> uint32_t host_features;
> - PartiallyBalloonedPage *pbp;
> +
> + /*
> + * Information about a partially ballooned page - does not have to be
> + * migrated and has to be reset on every device reset.
> + */
> + VirtIOPartiallyBalloonedPage pbp;
>
> bool qemu_4_0_config_size;
> } VirtIOBalloon;
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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