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 09:59, Don Slutz wrote:
> > On 12/02/14 09:26, Stefano Stabellini wrote:
> > > 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;
> 
> My testing shows that this should be:
> 
>         memorykb = ptr.max_memkb - (current_target_memkb + videoram) +
>             new_target_memkb;
> 
> As far as I can tell the reason for this is that memory/target (aka
> current_target_memkb) was set based on:
> 
>     new_target_memkb -= videoram;

Thank you very much for testing and the suggestion!

I think that the right fix for this is to remove videoram from
new_target_memkb earlier and only when the new target is absolute,
otherwise we risk removing videoram twice (in case the new target is
relative). I wonder why we didn't notice this before.


diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index d5d5204..4803cc4 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4744,13 +4744,17 @@ retry_transaction:
         goto out;
     }
 
+    videoram_s = libxl__xs_read(gc, t, libxl__sprintf(gc,
+                "%s/memory/videoram", dompath));
+    videoram = videoram_s ? atoi(videoram_s) : 0;
+
     if (relative) {
         if (target_memkb < 0 && abs(target_memkb) > current_target_memkb)
             new_target_memkb = 0;
         else
             new_target_memkb = current_target_memkb + target_memkb;
     } else
-        new_target_memkb = target_memkb;
+        new_target_memkb = target_memkb - videoram;
     if (new_target_memkb > memorykb) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR,
                 "memory_dynamic_max must be less than or equal to"
@@ -4766,9 +4770,6 @@ retry_transaction:
         abort_transaction = 1;
         goto out;
     }
-    videoram_s = libxl__xs_read(gc, t, libxl__sprintf(gc,
-                "%s/memory/videoram", dompath));
-    videoram = videoram_s ? atoi(videoram_s) : 0;
 
     if (enforce && new_target_memkb > 0) {
         memorykb = ptr.max_memkb - current_target_memkb + new_target_memkb;
@@ -4782,7 +4783,6 @@ retry_transaction:
         }
     }
 
-    new_target_memkb -= videoram;
     rc = xc_domain_set_pod_target(ctx->xch, domid,
             new_target_memkb / 4, NULL, NULL, NULL);
     if (rc != 0) {

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