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Re: [Xen-devel] [RFC 1/3] xen/balloon: Allow allocating DMA buffers



On 05/19/2018 01:04 AM, Boris Ostrovsky wrote:
On 05/17/2018 04:26 AM, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

A commit message would be useful.
Sure, v1 will have it

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

        for (i = 0; i < nr_pages; i++) {
-               page = alloc_page(gfp);
-               if (page == NULL) {
-                       nr_pages = i;
-                       state = BP_EAGAIN;
-                       break;
+               if (ext_pages) {
+                       page = ext_pages[i];
+               } else {
+                       page = alloc_page(gfp);
+                       if (page == NULL) {
+                               nr_pages = i;
+                               state = BP_EAGAIN;
+                               break;
+                       }
                }
                scrub_page(page);
                list_add(&page->lru, &pages);
@@ -529,7 +565,7 @@ static enum bp_state decrease_reservation(unsigned long 
nr_pages, gfp_t gfp)
        i = 0;
        list_for_each_entry_safe(page, tmp, &pages, lru) {
                /* XENMEM_decrease_reservation requires a GFN */
-               frame_list[i++] = xen_page_to_gfn(page);
+               frames[i++] = xen_page_to_gfn(page);
#ifdef CONFIG_XEN_HAVE_PVMMU
                /*
@@ -552,18 +588,22 @@ static enum bp_state decrease_reservation(unsigned long 
nr_pages, gfp_t gfp)
  #endif
                list_del(&page->lru);
- balloon_append(page);
+               if (!ext_pages)
+                       balloon_append(page);

So what you are proposing is not really ballooning. You are just
piggybacking on existing interfaces, aren't you?
Sort of. Basically I need to {increase|decrease}_reservation, not actually
allocating ballooned pages.
Do you think I can simply EXPORT_SYMBOL for {increase|decrease}_reservation?
Any other suggestion?
-boris


Thank you,
Oleksandr

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