Hi Michael:
Thanks for your review.
> From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Sent: Sunday, January 19, 2020 3:29 AM
> To: lantianyu1986@xxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang
> Zhang <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>; sashal@xxxxxxxxxx
> Cc: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; vkuznets <vkuznets@xxxxxxxxxx>;
> stable@xxxxxxxxxxxxxxx
> Subject: RE: [PATCH V2] x86/Hyper-V: Balloon up according to request page
> number
>
> From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Thursday, January 16,
> 2020 6:16 AM
> >
> > Current code has assumption that balloon request memory size aligns
> > with 2MB. But actually Hyper-V doesn't guarantee such alignment. When
> > balloon driver receives non-aligned balloon request, it produces
> > warning and balloon up more memory than requested in order to keep 2MB
> alignment.
> > Remove the warning and balloon up memory according to actual requested
> > memory size.
> >
> > Fixes: f6712238471a ("hv: hv_balloon: avoid memory leak on alloc_error
> > of 2MB memory
> > block")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> > ---
> > Change since v2:
> > - Change logic of switching alloc_unit from 2MB to 4KB
> > in the balloon_up() to avoid redundant iteration when
> > handle non-aligned page request.
> > - Remove 2MB alignment operation and comment in balloon_up()
> > ---
> > drivers/hv/hv_balloon.c | 12 ++++--------
> > 1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index
> > 7f3e7ab22d5d..536807efbc35 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -1684,7 +1684,7 @@ static unsigned int alloc_balloon_pages(struct
> > hv_dynmem_device *dm,
> > if (num_pages < alloc_unit)
> > return 0;
>
> The above test is no longer necessary. The num_pages < alloc_unit case is
> handled implicitly by your new 'for' loop condition.
>
Yes, will update in the next version.
> >
> > - for (i = 0; (i * alloc_unit) < num_pages; i++) {
> > + for (i = 0; i < num_pages / alloc_unit; i++) {
> > if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) >
> > HV_HYP_PAGE_SIZE)
> > return i * alloc_unit;
> > @@ -1722,7 +1722,7 @@ static unsigned int alloc_balloon_pages(struct
> > hv_dynmem_device *dm,
> >
> > }
> >
> > - return num_pages;
> > + return i * alloc_unit;
> > }
> >
> > static void balloon_up(union dm_msg_info *msg_info) @@ -1737,9
> > +1737,6 @@ static void balloon_up(union dm_msg_info *msg_info)
> > long avail_pages;
> > unsigned long floor;
> >
> > - /* The host balloons pages in 2M granularity. */
> > - WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0);
> > -
> > /*
> > * We will attempt 2M allocations. However, if we fail to
> > * allocate 2M chunks, we will go back to PAGE_SIZE allocations.
> > @@ -1749,14 +1746,13 @@ static void balloon_up(union dm_msg_info
> *msg_info)
> > avail_pages = si_mem_available();
> > floor = compute_balloon_floor();
> >
> > - /* Refuse to balloon below the floor, keep the 2M granularity. */
> > + /* Refuse to balloon below the floor. */
> > if (avail_pages < num_pages || avail_pages - num_pages < floor) {
> > pr_warn("Balloon request will be partially fulfilled. %s\n",
> > avail_pages < num_pages ? "Not enough memory." :
> > "Balloon floor reached.");
> >
> > num_pages = avail_pages > floor ? (avail_pages - floor) : 0;
> > - num_pages -= num_pages % PAGES_IN_2M;
> > }
> >
> > while (!done) {
> > @@ -1770,7 +1766,7 @@ static void balloon_up(union dm_msg_info
> *msg_info)
> > num_ballooned = alloc_balloon_pages(&dm_device,
> num_pages,
> > bl_resp, alloc_unit);
> >
> > - if (alloc_unit != 1 && num_ballooned == 0) {
> > + if (alloc_unit != 1 && num_ballooned != num_pages) {
>
> Maybe I'm missing something, but I don't think Vitaly's optimization works. If
> alloc_unit specifies 2 Mbytes, and num_pages specifies 3 Mbytes, then
> num_ballooned will come back as 2 Mbytes, which is correct. But if we revert
> alloc_unit to 1 page and "continue" in that case, we will lose the 2 Mbytes of
> memory (it's not freed), and the next time through the loop will try to allocate
> only 1 Mbyte (because num_pages will be decremented by num_ballooned). I
> think the original code does the right thing.
>
> Michael
Sorry. I should remove the "continue" here and then it will work. Will fix this in the
next version.
>
> > alloc_unit = 1;
> > continue;
> > }
> > --
> > 2.14.5
