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

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
       char *uuid;
       xs_transaction_t t;
   +    if (libxl_domain_info(ctx, &ptr, domid) < 0)
+        goto out_no_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.

I was talking about the line:

"rc=%d\n", domid, memorykb + LIBXL_MAXMEM_CONSTANT, rc);

(which is missing from the diff but is part of the LIBXL__LOG_ERRNO call). The
error message no longer matches what  xc_domain_setmaxmem() was called

   -Don Slutz

@@ -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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