This patch to the balloon driver eliminates the need for a user-space
program to slosh memory between domains and xen. This uses a proc
file at /proc/xen/memory_target. When read it reports memory the domain
owns in bytes. Writing a new value to the memory_target proc file
will cause the domain to exchange memory with xen to reach the target.
A xenolinux domain cannot grow bigger than it was when created.
Must be done by root.
Target requests are made in bytes, or with a k m or g suffix. The
request is parsed with the same function that parses the mem= boottime
kernel param.
Memory sizes in bytes are internally truncated to pages. Minimum change
is PAGE_SIZE (4k).
dragonfly:~# cat /proc/xen/memory_target
134217728l
dragonfly:~# echo 50m > /proc/xen/memory_target
Relinquish 78MB to xen. Domain now has 50MB
dragonfly:~# echo 100m > /proc/xen/memory_target
Reclaim 50MB from xen. Domain now has 100MB
dragonfly:~# cat /proc/xen/memory_target
104857600l
Daivd
(btw, updating twisted to 1.3 solved my console problems)
*** xeno-unstable.bk/linux-2.4.26-xen-sparse/arch/xen/drivers/balloon/balloon.c
Tue Jul 6 15:09:30 2004
---
obj-unstable/xeno-unstable.bk/linux-2.4.26-xen-sparse/arch/xen/drivers/balloon/balloon.c
Fri Jul 16 15:12:11 2004
***************
*** 39,44 ****
--- 39,45 ----
static struct proc_dir_entry *balloon_pde;
unsigned long credit;
+ static unsigned long current_pages, max_pages;
static inline pte_t *get_ptep(unsigned long addr)
{
***************
*** 221,270 ****
return ret;
}
static int balloon_write(struct file *file, const char *buffer,
u_long count, void *data)
{
! user_balloon_op_t bop;
/* Only admin can play with the balloon :) */
if ( !capable(CAP_SYS_ADMIN) )
return -EPERM;
! if ( copy_from_user(&bop, buffer, sizeof(bop)) )
return -EFAULT;
! switch ( bop.op )
! {
! case USER_INFLATE_BALLOON:
! if ( inflate_balloon(bop.size) < bop.size )
! return -EAGAIN;
! break;
!
! case USER_DEFLATE_BALLOON:
! deflate_balloon(bop.size);
! break;
! default:
! printk("Unknown command to balloon driver.");
! return -EFAULT;
}
! return sizeof(bop);
}
static int __init init_module(void)
{
printk(KERN_ALERT "Starting Xen Balloon driver\n");
! credit = 0;
!
! if ( (balloon_pde = create_xen_proc_entry("balloon", 0600)) == NULL )
{
printk(KERN_ALERT "Unable to create balloon driver proc entry!");
return -1;
}
balloon_pde->write_proc = balloon_write;
return 0;
}
--- 222,307 ----
return ret;
}
+ #define PAGE_TO_MB_SHIFT 8
+
static int balloon_write(struct file *file, const char *buffer,
u_long count, void *data)
{
! char memstring[64], *endchar;
! int len, i, pages;
! unsigned long long target;
/* Only admin can play with the balloon :) */
if ( !capable(CAP_SYS_ADMIN) )
return -EPERM;
! if (count>sizeof memstring) {
! return -EFBIG;
! }
!
! len = strnlen_user(buffer, count);
! if (len==0) return -EBADMSG;
! if (len==1) return 1; /* input starts with a NUL char */
! if ( strncpy_from_user(memstring, buffer, len) < 0)
return -EFAULT;
! endchar = memstring;
! for(i=0; i<len; ++i,++endchar) {
! if ('0'>memstring[i] || memstring[i]>'9') break;
! }
! if (i==0) return -EBADMSG;
! target = memparse(memstring,&endchar);
! pages = target >> PAGE_SHIFT;
!
! if (pages < current_pages) {
! int change = inflate_balloon(current_pages-pages);
! if (change<0) return change;
!
! current_pages -= change;
! printk("Relinquish %dMB to xen. Domain now has %dMB\n",
! change>>PAGE_TO_MB_SHIFT, current_pages>>PAGE_TO_MB_SHIFT);
}
+ else if (pages > current_pages) {
+ int change = deflate_balloon(min(pages,max_pages) - current_pages);
+ if (change<0) return change;
! current_pages += change;
! printk("Reclaim %dMB from xen. Domain now has %dMB\n",
! change>>PAGE_TO_MB_SHIFT, current_pages>>PAGE_TO_MB_SHIFT);
! }
!
! return len;
! }
!
!
! static int balloon_read(char *page, char **start, off_t off,
! int count, int *eof, void *data)
! {
! int len;
! len = sprintf(page,"%ul\n",current_pages<<PAGE_SHIFT);
!
! if (len <= off+count) *eof = 1;
! *start = page + off;
! len -= off;
! if (len>count) len = count;
! if (len<0) len = 0;
! return len;
}
static int __init init_module(void)
{
printk(KERN_ALERT "Starting Xen Balloon driver\n");
! max_pages = current_pages = start_info.nr_pages;
! if ( (balloon_pde = create_xen_proc_entry("memory_target", 0644)) == NULL
)
{
printk(KERN_ALERT "Unable to create balloon driver proc entry!");
return -1;
}
balloon_pde->write_proc = balloon_write;
+ balloon_pde->read_proc = balloon_read;
return 0;
}
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