Re: [Xen-devel] [PATCH Remus v1 1/8] tools/libxc: adjust the memory allocation for migration

[Hongyang Yang <yanghy@xxxxxxxxxxxxxx>]

Hi Ian,

On 05/07/2015 09:57 PM, Ian Campbell wrote:
> On Thu, 2015-05-07 at 21:42 +0800, Hongyang Yang wrote:
> > On 05/07/2015 05:48 PM, Andrew Cooper wrote:
> > > On 07/05/15 07:37, Yang Hongyang wrote:
> > > > Move the memory allocation before the concrete live/nolive save
> > > > in order to avoid the free/alloc memory loop when using Remus.
> > > >
> > > > Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> > > > ---
> > > >    tools/libxc/xc_sr_save.c | 53 
> > > > +++++++++++++++++++-----------------------------
> > > >    1 file changed, 21 insertions(+), 32 deletions(-)
> > > >
> > > > diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
> > > > index 5d9c267..7fed668 100644
> > > > --- a/tools/libxc/xc_sr_save.c
> > > > +++ b/tools/libxc/xc_sr_save.c
> > > > @@ -3,6 +3,8 @@
> > > >
> > > >    #include "xc_sr_common.h"
> > > >
> > > > +DECLARE_HYPERCALL_BUFFER(unsigned long, to_send);
> > > This unfortunately causes an issue when concurrent calls to
> > > xc_domain_save() in the same process.  While this is a highly
> > > ill-advised action, I did try to avoid breaking it.
> > >
> > > Please move this declaration into the ctx.save union.
> > I know the best way is to put this into ctx.save union, but I haven't
> > found a method to put it in, the DECLARE_HYPERCALL_BUFFER macro can not
> > be used there, should I just define a unsigned long var at ctx.save
> > union, and use other macro(what macro?) define at save()?
> I think you need a variable of type xc_hypercall_buffer_t in the struct
> and then to use DECLARE_HYPERCALL_BUFFER_SHADOW in functions which need
> to access it.
>
> DECLARE_HYPERCALL_BUFFER_SHADOW seems to currently be unused, David
> added it in 60572c972b8d, I suspect to be used by migration v2, although
> perhaps it never was (at least not in tree yet).
Thank you for the information, I finally found the way to use it, but I
had to add a new macro DECLARE_HYPERCALL_BUFFER_USER_POINTER which let
me to define a user pointer to access the buffer data, because in
send_all_pages() I only need to access the buffer data, if I use
DECLARE_HYPERCALL_BUFFER_SHADOW, it will define a shadow hypercall
buffer which I don't use and the compiler will report unused var error.

I will send out v2 series which you can see clearly what I've described
above.

> Ian.
>
> .
--
Thanks,
Yang.

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