Re: [Xen-devel] [PATCH v2 for-4.6] libxl_set_memory_target: retain the same maxmem offset on top of the current target

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 2 Dec 2014, Don Slutz wrote:
> On 12/02/14 06:53, Stefano Stabellini wrote:
> > In libxl_set_memory_target when setting the new maxmem, retain the same
> > offset on top of the current target. The offset includes memory
> > allocated by QEMU for rom files.
> > 
> > Signed-off-by: Stefano Stabellini<stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > ---
> > 
> > Changes in v2:
> > - call libxl_domain_info instead of libxl_dominfo_init;
> > - call libxl_domain_info before retry_transaction.
> > 
> > diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> > index de23fec..569a32a 100644
> > --- a/tools/libxl/libxl.c
> > +++ b/tools/libxl/libxl.c
> > @@ -4694,6 +4694,9 @@ int libxl_set_memory_target(libxl_ctx *ctx, uint32_t
> > domid,
> >       char *uuid;
> >       xs_transaction_t t;
> >   +    if (libxl_domain_info(ctx, &ptr, domid) < 0)
> > +        goto out_no_transaction;
> > +
> >   retry_transaction:
> >       t = xs_transaction_start(ctx->xsh);
> >   @@ -4767,10 +4770,9 @@ retry_transaction:
> >                   "%s/memory/videoram", dompath));
> >       videoram = videoram_s ? atoi(videoram_s) : 0;
> >   -    if (enforce) {
> > -        memorykb = new_target_memkb;
> > -        rc = xc_domain_setmaxmem(ctx->xch, domid, memorykb +
> > -                LIBXL_MAXMEM_CONSTANT);
> > +    if (enforce && new_target_memkb > 0) {
> > +        memorykb = ptr.max_memkb - current_target_memkb + new_target_memkb;
> > +        rc = xc_domain_setmaxmem(ctx->xch, domid, memorykb);
> >           if (rc != 0) {
> >               LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
> >                       "xc_domain_setmaxmem domid=%d memkb=%d failed "
> 
> You need to remove LIBXL_MAXMEM_CONSTANT here also.

I don't think so: LIBXL_MAXMEM_CONSTANT is supposed to be a safety
buffer and we should keep it as is across libxl_set_memory_target calls.
Arguably LIBXL_MAXMEM_CONSTANT could be removed entirely with the
proposed QEMU changes but that is a separate matter.

 
> > @@ -4800,8 +4802,6 @@ retry_transaction:
> >           goto out;
> >       }
> >   -    libxl_dominfo_init(&ptr);
> > -    xcinfo2xlinfo(ctx, &info, &ptr);
> >       uuid = libxl__uuid2string(gc, ptr.uuid);
> >       libxl__xs_write(gc, t, libxl__sprintf(gc, "/vm/%s/memory", uuid),
> >               "%"PRIu32, new_target_memkb / 1024);
> 

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