> -----Original Message-----
> From: Jason Wang [mailto:jasow...@redhat.com]
> Sent: Monday, November 24, 2014 15:28 PM
> To: Dexuan Cui; gre...@linuxfoundation.org; linux-ker...@vger.kernel.org;
> driverdev-devel@linuxdriverproject.org; o...@aepfle.de;
> a...@canonical.com; KY Srinivasan
> Cc: Haiyang Zhang
> Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on alloc_error of
> 2MB memory block
>
> On 11/24/2014 02:08 PM, Dexuan Cui wrote:
> >> -----Original Message-----
> >> > From: Jason Wang [mailto:jasow...@redhat.com]
> >> > Sent: Monday, November 24, 2014 13:18 PM
> >> > To: Dexuan Cui; gre...@linuxfoundation.org; linux-
> ker...@vger.kernel.org;
> >> > driverdev-devel@linuxdriverproject.org; o...@aepfle.de;
> >> > a...@canonical.com; KY Srinivasan
> >> > Cc: Haiyang Zhang
> >> > Subject: Re: [PATCH] hv: hv_balloon: avoid memory leak on
> alloc_error of
> >> > 2MB memory block
> >> >
> >> > On 11/24/2014 01:56 PM, Dexuan Cui wrote:
> >>> > > If num_ballooned is not 0, we shouldn't neglect the already-
> allocated
> >> > 2MB
> >>> > > memory block(s).
> >>> > >
> >>> > > Cc: K. Y. Srinivasan <k...@microsoft.com>
> >>> > > Cc: <sta...@vger.kernel.org>
> >>> > > Signed-off-by: Dexuan Cui <de...@microsoft.com>
> >>> > > ---
> >>> > > drivers/hv/hv_balloon.c | 4 +++-
> >>> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> >>> > >
> >>> > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> >>> > > index 5e90c5d..cba2d3b 100644
> >>> > > --- a/drivers/hv/hv_balloon.c
> >>> > > +++ b/drivers/hv/hv_balloon.c
> >>> > > @@ -1091,6 +1091,8 @@ static void balloon_up(struct
> work_struct
> >> > *dummy)
> >>> > > bool done = false;
> >>> > > int i;
> >>> > >
> >>> > > + /* The host does balloon_up in 2MB. */
> >>> > > + WARN_ON(num_pages % PAGES_IN_2M != 0);
> >>> > >
> >>> > > /*
> >>> > > * We will attempt 2M allocations. However, if we fail to
> >>> > > @@ -1111,7 +1113,7 @@ static void balloon_up(struct
> work_struct
> >> > *dummy)
> >>> > > bl_resp, alloc_unit,
> >>> > > &alloc_error);
> >>> > >
> >>> > > - if ((alloc_error) && (alloc_unit != 1)) {
> >>> > > + if (alloc_error && (alloc_unit != 1) &&
> num_ballooned == 0)
> >> > {
> >>> > > alloc_unit = 1;
> >>> > > continue;
> >>> > > }
> >> >
> >> > Before the change, we may retry the 4K allocation when part or all 2M
> >> > allocations were failed. This makes sense when memory is fragmented.
> But
> > Yes, but all the partially-allocated 2MB memory blocks are lost(mem leak).
> >
> >> > after the change, if part of 2M allocation were failed, we won't retry
> >> > 4K allocation. Is this expected?
> > Hi Jason,
> > The patch doesn't break the "try 2MB first; then try 4K" logic:
> >
> > With the change, we'll retry the 2MB allocation in the next iteration of the
> > same while (!done) loop -- we expect this retry will cause
> > "alloc_error && (alloc_unit != 1) && num_ballooned == 0" to be true,
> > so we'll later try 4K allocation, as we did before.
>
> If I read the code correctly, if part of 2M allocation fails.
> alloc_balloon_pages() will have a non zero return value with alloc_error
> set. Then it will match the following check:
>
> if ((alloc_error) || (num_ballooned == num_pages))
> {
>
> which will set done to true. So there's no second iteration of while
> (!done) loop?
Oh... I see the issue in my patch.
Thanks for pointing this out, Jason!
> Probably you need something like:
>
> if ((alloc_unit != 1) && (num_ballooned == 0)) {
> alloc_unit = 1;
> continue;
> }
>
> if ((alloc_unit == 1) || (num_ballooned == num_pages)) {
> ...
> }
Your code is good, except for one thing:
alloc_balloon_pages() can return due to:
if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) >
PAGE_SIZE)
return i * alloc_unit;
In this case, "alloc_unit == 1" is true, but we shouldn't run "done = true".
How do you like this? I made a few changes based on your code.
@@ -1086,16 +1088,18 @@ 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);
- if ((alloc_error) && (alloc_unit != 1)) {
+ if (alloc_unit != 1 && num_ballooned == 0) {
alloc_unit = 1;
continue;
}
- if ((alloc_error) || (num_ballooned == num_pages)) {
+ if ((alloc_unit == 1 && alloc_error) ||
+ (num_ballooned == num_pages)) {
bl_resp->more_pages = 0;
done = true;
dm_device.state = DM_INITIALIZED;
If you're Ok with this, I'll send out a v2 patch.
Thanks,
-- Dexuan
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