Re: [Xen-changelog] fail domU creation if memory need couldn't be succeed after ballooning out dom0

Re: [Xen-changelog] fail domU creation if memory need couldn't be succeed after ballooning out dom0

[Anthony Liguori]

I don't mean to pick on this patch, but I've been chasing down a number 
of race conditions in Xend that mostly seem to be rooted in the fact 
that we do a lot of timeouts.

In general, we should try to avoid using timeouts at all cost.  If we do 
have to use a timeout, then we should make sure it's long enough that 
the timeout is never going to happen.  It's surprisingly easy to have 
enough load on your system such you miss a 2 second timeout.

Getting rid of this timeout would be difficult so for now, we should at 
least bump it to 30 or 60 seconds.

Thanks,

Anthony Liguori

Xen patchbot -unstable wrote:

>diff -r 02789fed726a -r a06430752462 tools/python/xen/xm/create.py
>--- a/tools/python/xen/xm/create.py	Wed Aug 17 23:11:56 2005
>+++ b/tools/python/xen/xm/create.py	Thu Aug 18 01:13:49 2005
>@@ -23,6 +23,7 @@
> import sys
> import socket
> import commands
>+import time
> 
> import xen.lowlevel.xc
> 
>@@ -674,18 +675,33 @@
>     return 0
> 
> def balloon_out(dom0_min_mem, opts):
>-    """Balloon out to get memory for domU, if necessarily"""
>+    """Balloon out memory from dom0 if necessary"""
>     SLACK = 4
>+    timeout = 20 # 2s
>+    ret = 0
> 
>     xc = xen.lowlevel.xc.new()
>     pinfo = xc.physinfo()
>-    free_mem = pinfo['free_pages']/256
>-    if free_mem < opts.vals.memory + SLACK:
>-        need_mem = opts.vals.memory + SLACK - free_mem
>-        cur_alloc = get_dom0_alloc()
>-        if cur_alloc - need_mem >= dom0_min_mem:
>-            server.xend_domain_mem_target_set(0, cur_alloc - need_mem)
>+    free_mem = pinfo['free_pages'] / 256
>+    domU_need_mem = opts.vals.memory + SLACK 
>+
>+    dom0_cur_alloc = get_dom0_alloc()
>+    dom0_new_alloc = dom0_cur_alloc - (domU_need_mem - free_mem)
>+
>+    if free_mem < domU_need_mem and dom0_new_alloc >= dom0_min_mem:
>+
>+        server.xend_domain_mem_target_set(0, dom0_new_alloc)
>+
>+        while dom0_cur_alloc > dom0_new_alloc and timeout > 0:
>+            time.sleep(0.1) # sleep 100ms
>+            dom0_cur_alloc = get_dom0_alloc()
>+            timeout -= 1
>+        
>+        if dom0_cur_alloc > dom0_new_alloc:
>+            ret = 1
>+    
>     del xc
>+    return ret
> 
> def main(argv):
>     random.seed()
>@@ -717,7 +733,8 @@
>     else:
>         dom0_min_mem = xroot.get_dom0_min_mem()
>         if dom0_min_mem != 0:
>-            balloon_out(dom0_min_mem, opts)
>+            if balloon_out(dom0_min_mem, opts):
>+                return
> 
>         dom = make_domain(opts, config)
>         if opts.vals.console_autoconnect:
>
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