core-admin/qmemman/qmemman_algo.py

import string

# This are only defaults - can be overriden by QMemmanServer with values from
# config file
CACHE_FACTOR = 1.3
MIN_PREFMEM = 200*1024*1024
DOM0_MEM_BOOST = 350*1024*1024

#untrusted meminfo size is taken from xenstore key, thus its size is limited
#so splits do not require excessive memory
def parse_meminfo(untrusted_meminfo):
    untrusted_dict = {}
#split meminfo contents into lines
    untrusted_lines = string.split(untrusted_meminfo,"\n")
    for untrusted_lines_iterator in untrusted_lines:
#split a single meminfo line into words
        untrusted_words = string.split(untrusted_lines_iterator)
        if len(untrusted_words) >= 2:
            untrusted_dict[string.rstrip(untrusted_words[0], ":")] = untrusted_words[1]

    return untrusted_dict

def is_meminfo_suspicious(domain, untrusted_meminfo):
    ret = False
    
#check whether the required keys exist and are not negative
    try:
        for i in ('MemTotal', 'MemFree', 'Buffers', 'Cached', 'SwapTotal', 'SwapFree'):
            val = int(untrusted_meminfo[i])*1024
            if (val < 0):
                ret = True
            untrusted_meminfo[i] = val
    except:
        ret = True

    if not ret and untrusted_meminfo['SwapTotal'] < untrusted_meminfo['SwapFree']:
        ret = True
    if not ret and untrusted_meminfo['MemTotal'] < untrusted_meminfo['MemFree'] + untrusted_meminfo['Cached'] + untrusted_meminfo['Buffers']:
        ret = True
#we could also impose some limits on all the above values
#but it has little purpose - all the domain can gain by passing e.g. 
#very large SwapTotal is that it will be assigned all free Xen memory
#it can be achieved with legal values, too, and it will not allow to
#starve existing domains, by design
    if ret:
        print 'suspicious meminfo for domain', domain.id, 'mem actual', domain.memory_actual, untrusted_meminfo
    return ret

#called when a domain updates its 'meminfo' xenstore key
def refresh_meminfo_for_domain(domain, untrusted_xenstore_key):
    untrusted_meminfo = parse_meminfo(untrusted_xenstore_key)
    if untrusted_meminfo is None:
        domain.meminfo = None
        return
#sanitize start
    if is_meminfo_suspicious(domain, untrusted_meminfo):
#sanitize end
        domain.meminfo = None
        domain.mem_used = None
    else:
#sanitized, can assign
        domain.meminfo = untrusted_meminfo
        domain.mem_used =  domain.meminfo['MemTotal'] - domain.meminfo['MemFree'] - domain.meminfo['Cached'] - domain.meminfo['Buffers'] + domain.meminfo['SwapTotal'] - domain.meminfo['SwapFree']
                        
def prefmem(domain):
#dom0 is special, as it must have large cache, for vbds. Thus, give it a special boost
    if domain.id == '0':
        return min(domain.mem_used*CACHE_FACTOR + 350*1024*1024, domain.memory_maximum)
    return max(min(domain.mem_used*CACHE_FACTOR, domain.memory_maximum), MIN_PREFMEM)

def memory_needed(domain):
#do not change
#in balance(), "distribute total_available_memory proportionally to mempref" relies on this exact formula
    ret = prefmem(domain) - domain.memory_actual
    return ret
    
#prepare list of (domain, memory_target) pairs that need to be passed
#to "xm memset" equivalent in order to obtain "memsize" of memory
#return empty list when the request cannot be satisfied
def balloon(memsize, domain_dictionary):
    REQ_SAFETY_NET_FACTOR = 1.05
    donors = list()
    request = list()
    available = 0
    for i in domain_dictionary.keys():
        if domain_dictionary[i].meminfo is None:
            continue
        if domain_dictionary[i].no_progress:
            continue
        need = memory_needed(domain_dictionary[i])
        if need < 0:
            print 'balloon: dom' , i, 'has actual memory', domain_dictionary[i].memory_actual
            donors.append((i,-need))
            available-=need   
    print 'req=', memsize, 'avail=', available, 'donors', donors
    if available<memsize:
        return ()
    scale = 1.0*memsize/available
    for donors_iter in donors:
        id, mem = donors_iter
        memborrowed = mem*scale*REQ_SAFETY_NET_FACTOR
        print 'borrow' , memborrowed, 'from', id
        memtarget = int(domain_dictionary[id].memory_actual - memborrowed)
        request.append((id, memtarget))
    return request
# REQ_SAFETY_NET_FACTOR is a bit greater that 1. So that if the domain yields a bit less than requested, due
# to e.g. rounding errors, we will not get stuck. The surplus will return to the VM during "balance" call.


#redistribute positive "total_available_memory" of memory between domains, proportionally to prefmem
def balance_when_enough_memory(domain_dictionary, xen_free_memory, total_mem_pref, total_available_memory):
    print 'balance_when_enough_memory(', xen_free_memory, total_mem_pref, total_available_memory, ')'
    target_memory = {}
    # memory not assigned because of static max
    left_memory = 0
    acceptors_count = 0
    for i in domain_dictionary.keys():
        if domain_dictionary[i].meminfo is None:
            continue
        if domain_dictionary[i].no_progress:
            continue
#distribute total_available_memory proportionally to mempref
        scale = 1.0*prefmem(domain_dictionary[i])/total_mem_pref
        target_nonint = prefmem(domain_dictionary[i]) + scale*total_available_memory
#prevent rounding errors
        target = int(0.999*target_nonint)
#do not try to give more memory than static max
        if target > domain_dictionary[i].memory_maximum:
            left_memory += target-domain_dictionary[i].memory_maximum
            target = domain_dictionary[i].memory_maximum
        else:
# count domains which can accept more memory
            acceptors_count += 1
        target_memory[i] = target
# distribute left memory across all acceptors
    while left_memory > 0 and acceptors_count > 0:
        print '  left_memory:', left_memory, 'acceptors_count:', acceptors_count
        new_left_memory = 0
        new_acceptors_count = acceptors_count
        for i in target_memory.keys():
            target = target_memory[i]
            if target < domain_dictionary[i].memory_maximum:
                memory_bonus = int(0.999*(left_memory/acceptors_count))
                if target+memory_bonus >= domain_dictionary[i].memory_maximum:
                    new_left_memory += target+memory_bonus - domain_dictionary[i].memory_maximum
                    target = domain_dictionary[i].memory_maximum
                    new_acceptors_count -= 1
                else:
                    target += memory_bonus
            target_memory[i] = target
        left_memory = new_left_memory
        acceptors_count = new_acceptors_count
# split target_memory dictionary to donors and acceptors
#  this is needed to first get memory from donors and only then give it to acceptors
    donors_rq = list()
    acceptors_rq = list()
    for i in target_memory.keys():
        target = target_memory[i]
        if (target < domain_dictionary[i].memory_actual):
            donors_rq.append((i, target))
        else:
            acceptors_rq.append((i, target))

#    print 'balance(enough): xen_free_memory=', xen_free_memory, 'requests:', donors_rq + acceptors_rq
    return donors_rq + acceptors_rq

#when not enough mem to make everyone be above prefmem, make donors be at prefmem, and 
#redistribute anything left between acceptors
def balance_when_low_on_memory(domain_dictionary, xen_free_memory, total_mem_pref_acceptors, donors, acceptors):
    donors_rq = list()
    acceptors_rq = list()
    squeezed_mem = xen_free_memory
    for i in donors:
        avail = -memory_needed(domain_dictionary[i])
        if avail < 10*1024*1024:
            #probably we have already tried making it exactly at prefmem, give up
            continue
        squeezed_mem -= avail
        donors_rq.append((i, prefmem(domain_dictionary[i])))
#the below can happen if initially xen free memory is below 50M
    if squeezed_mem < 0:
        return donors_rq
    for i in acceptors:
        scale = 1.0*prefmem(domain_dictionary[i])/total_mem_pref_acceptors
        target_nonint = domain_dictionary[i].memory_actual + scale*squeezed_mem
#do not try to give more memory than static max
        target = min(int(0.999*target_nonint), domain_dictionary[i].memory_maximum)
        acceptors_rq.append((i, target))
#    print 'balance(low): xen_free_memory=', xen_free_memory, 'requests:', donors_rq + acceptors_rq
    return donors_rq + acceptors_rq


#redistribute memory across domains
#called when one of domains update its 'meminfo' xenstore key 
#return the list of (domain, memory_target) pairs to be passed to
#"xm memset" equivalent 
def balance(xen_free_memory, domain_dictionary):

#sum of all memory requirements - in other words, the difference between
#memory required to be added to domains (acceptors) to make them be at their 
#preferred memory, and memory that can be taken from domains (donors) that
#can provide memory. So, it can be negative when plenty of memory.
    total_memory_needed = 0

#sum of memory preferences of all domains
    total_mem_pref = 0

#sum of memory preferences of all domains that require more memory
    total_mem_pref_acceptors = 0
    
    donors = list()	# domains that can yield memory
    acceptors = list()  # domains that require more memory
#pass 1: compute the above "total" values
    for i in domain_dictionary.keys():
        if domain_dictionary[i].meminfo is None:
            continue
        if domain_dictionary[i].no_progress:
            continue
        need = memory_needed(domain_dictionary[i])
#        print 'domain' , i, 'act/pref', domain_dictionary[i].memory_actual, prefmem(domain_dictionary[i]), 'need=', need
        if need < 0 or domain_dictionary[i].memory_actual >= domain_dictionary[i].memory_maximum:
            donors.append(i)
        else:
            acceptors.append(i)
            total_mem_pref_acceptors += prefmem(domain_dictionary[i])
        total_memory_needed += need
        total_mem_pref += prefmem(domain_dictionary[i])

    total_available_memory = xen_free_memory - total_memory_needed  
    if total_available_memory > 0:
        return balance_when_enough_memory(domain_dictionary, xen_free_memory, total_mem_pref, total_available_memory)
    else:
        return balance_when_low_on_memory(domain_dictionary, xen_free_memory, total_mem_pref_acceptors, donors, acceptors)