From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
... and simplify alloc_balloon_pages() interface by removing redundant
alloc_error from it.
If we happen to enter balloon_up() with balloon_wrk.num_pages = 0 we will enter
infinite 'while (!done)' loop as alloc_balloon_pages() will be always returning
0 and not setting alloc_error. We will also be sending a meaningless message to
the host on every iteration.
The 'alloc_unit == 1 && alloc_error -> num_ballooned == 0' change and
alloc_error elimination requires a special comment. We do alloc_balloon_pages()
with 2 different alloc_unit values and there are 4 different
alloc_balloon_pages() results, let's check them all.
alloc_unit = 512:
1) num_ballooned = 0, alloc_error = 0: we do 'alloc_unit=1' and retry pre- and
post-patch.
2) num_ballooned > 0, alloc_error = 0: we check 'num_ballooned == num_pages'
and act accordingly, pre- and post-patch.
3) num_ballooned > 0, alloc_error > 0: we report this chunk and remain within
the loop, no changes here.
4) num_ballooned = 0, alloc_error > 0: we do 'alloc_unit=1' and retry pre- and
post-patch.
alloc_unit = 1:
1) num_ballooned = 0, alloc_error = 0: this can happen in two cases: when we
passed 'num_pages=0' to alloc_balloon_pages() or when there was no space in
bl_resp to place a single response. The second option is not possible as
bl_resp is of PAGE_SIZE size and single response 'union dm_mem_page_range' is
8 bytes, but the first one is (in theory, I think that Hyper-V host never
places such requests). Pre-patch code loops forever, post-patch code sends
a reply with more_pages = 0 and finishes.
2) num_ballooned > 0, alloc_error = 0: we ran out of space in bl_resp, we
report partial success and remain within the loop, no changes pre- and
post-patch.
3) num_ballooned > 0, alloc_error > 0: pre-patch code finishes, post-patch code
does one more try and if there is no progress (we finish with
'num_ballooned = 0') we finish. So we try a bit harder with this patch.
4) num_ballooned = 0, alloc_error > 0: both pre- and post-patch code enter
'more_pages = 0' branch and finish.
So this patch has two real effects:
1) We reply with an empty response to 'num_pages=0' request.
2) We try a bit harder on alloc_unit=1 allocations (and reply with an empty
tail reply in case we fail).
An empty reply should be supported by host as we were able to send it even with
pre-patch code when we were not able to allocate a single page.
Suggested-by: Laszlo Ersek <lersek@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
---
drivers/hv/hv_balloon.c | 19 ++++++-------------
1 files changed, 6 insertions(+), 13 deletions(-)
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 4f5323c..74312c8 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1081,9 +1081,9 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
-static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
- struct dm_balloon_response *bl_resp, int alloc_unit,
- bool *alloc_error)
+static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
+ struct dm_balloon_response *bl_resp,
+ int alloc_unit)
{
int i = 0;
struct page *pg;
@@ -1104,11 +1104,8 @@ static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
__GFP_NOMEMALLOC | __GFP_NOWARN,
get_order(alloc_unit << PAGE_SHIFT));
- if (!pg) {
- *alloc_error = true;
+ if (!pg)
return i * alloc_unit;
- }
-
dm->num_pages_ballooned += alloc_unit;
@@ -1140,7 +1137,6 @@ static void balloon_up(struct work_struct *dummy)
struct dm_balloon_response *bl_resp;
int alloc_unit;
int ret;
- bool alloc_error;
bool done = false;
int i;
struct sysinfo val;
@@ -1173,18 +1169,15 @@ static void balloon_up(struct work_struct *dummy)
num_pages -= num_ballooned;
- alloc_error = false;
num_ballooned = alloc_balloon_pages(&dm_device, num_pages,
- bl_resp, alloc_unit,
- &alloc_error);
+ bl_resp, alloc_unit);
if (alloc_unit != 1 && num_ballooned == 0) {
alloc_unit = 1;
continue;
}
- if ((alloc_unit == 1 && alloc_error) ||
- (num_ballooned == num_pages)) {
+ if (num_ballooned == 0 || num_ballooned == num_pages) {
bl_resp->more_pages = 0;
done = true;
dm_device.state = DM_INITIALIZED;
--
1.7.4.1
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