linux-kernel - RE: [PATCH 1/1] hv_balloon: Enable hot-add for memblock sizes

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Message-ID:
 <SN6PR02MB41571838C410EB52F328A461D4162@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Fri, 26 Apr 2024 16:35:42 +0000
From: Michael Kelley <mhklinux@...look.com>
To: David Hildenbrand <david@...hat.com>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
	"decui@...rosoft.com" <decui@...rosoft.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>
Subject: RE: [PATCH 1/1] hv_balloon: Enable hot-add for memblock sizes > 128
 Mbytes

From: David Hildenbrand <david@...hat.com> Sent: Friday, April 26, 2024 1:59 AM
> 
> On 11.03.24 19:12, mhkelley58@...il.com wrote:
> >
> > Fix this problem by having the Hyper-V balloon driver determine
> > the Linux memblock size, and process hot-add requests in that
> > chunk size instead of a fixed 128 Mbytes. Also update the hot-add
> > alignment requested of the Hyper-V host to match the memblock
> > size instead of being a fixed 128 Mbytes.
> 
> That way, we should never be getting unaligned ranges IIRC, correct? I
> think we added ways in QEMU to guarantee that for the HV-balloon
> implementation as well.

Correct.

> 
> >
> > The code changes look significant, but in fact are just a
> 
> Nah, it's okay :)
> 
> > simple text substitution of a new global variable for the
> > previous HA_CHUNK constant. No algorithms are changed except
> > to initialize the new global variable and to calculate the
> > alignment value to pass to Hyper-V. Testing with memblock
> > sizes of 256 Mbytes and 2 Gbytes shows correct operation.
> >
> > Signed-off-by: Michael Kelley <mhklinux@...look.com>
> > ---
> >   drivers/hv/hv_balloon.c | 64 ++++++++++++++++++++++++-----------------
> >   1 file changed, 37 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
> > index e000fa3b9f97..d3bfbf3d274a 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -425,11 +425,11 @@ struct dm_info_msg {
> >    * The range start_pfn : end_pfn specifies the range
> >    * that the host has asked us to hot add. The range
> >    * start_pfn : ha_end_pfn specifies the range that we have
> > - * currently hot added. We hot add in multiples of 128M
> > - * chunks; it is possible that we may not be able to bring
> > - * online all the pages in the region. The range
> > + * currently hot added. We hot add in chunks equal to the
> > + * memory block size; it is possible that we may not be able
> > + * to bring online all the pages in the region. The range
> >    * covered_start_pfn:covered_end_pfn defines the pages that can
> > - * be brough online.
> > + * be brought online.
> >    */
> >
> >   struct hv_hotadd_state {
> > @@ -505,8 +505,9 @@ enum hv_dm_state {
> >
> >   static __u8 recv_buffer[HV_HYP_PAGE_SIZE];
> >   static __u8 balloon_up_send_buffer[HV_HYP_PAGE_SIZE];
> > +static unsigned long ha_chunk_pgs;
> 
> Why not stick to PAGES_IN_2M and call this
> 
> ha_pages_in_chunk? Much easier to get than "pgs".

OK.  I was trying to keep the new identifier short so that
mechanically substituting it for HA_CHUNK didn't blow up
the line length.

> 
> Apart from that looks good. Some helper macros to convert size to chunks
> etc. might make the code even more readable.

I'll look at this.  Might help the line length problem too.

Thanks for the review.

Michael