#!/usr/bin/python3
# Copyright 2017 Facebook.
# Licensed under the same terms as memcached itself.
import argparse
import socket
import sys
import re
import traceback
from time import sleep, time
parser = argparse.ArgumentParser(description="daemon for rebalancing slabs")
parser.add_argument("--host", help="host to connect to",
default="localhost:11211", metavar="HOST:PORT")
parser.add_argument("-s", "--sleep", help="seconds between runs",
type=int, default="1")
parser.add_argument("-v", "--verbose", action="store_true")
parser.add_argument("-a", "--automove", action="store_true", default=False,
help="enable automatic page rebalancing")
parser.add_argument("-w", "--window", type=int, default="30",
help="rolling window size for decision history")
parser.add_argument("-r", "--ratio", type=float, default=0.8,
help="ratio limiting distance between low/high class ages")
parser.add_argument("-f", "--free", type=float, default=0.005,
help="free chunks/pages buffer ratio")
parser.add_argument("-z", "--size", type=int, default=512,
help="item size cutoff for storage")
args = parser.parse_args()
host, port = args.host.split(':')
MIN_PAGES_FOR_SOURCE = 2
MIN_PAGES_FOR_RECLAIM = 2.5
MIN_PAGES_FREE = 1.5
MEMCHECK_PERIOD = 60
def window_check(history, sid, key):
total = 0
for window in history['w']:
s = window.get(sid)
if s and s.get(key):
total += s.get(key)
return total
def window_key_check(history, key):
total = 0
for window in history['w']:
v = window.get(key)
if v:
total += v
return total
def determine_move(history, stats, diffs, memfree):
""" Figure out of a page move is in order.
- Use as much memory as possible to hold items, reducing the load on
flash.
- tries to keep the global free page pool inbetween poolmin/poolmax.
- avoids flapping as much as possible:
- only pull pages off of a class if it hasn't recently evicted or allocated pages.
- only pull pages off if a sufficient number of free chunks are available.
- if global pool is below minimum remove pages from oldest large class.
- if global pool is above maximum, move pages to youngest large class.
- extstore manages a desired number of free chunks in each slab class.
- automover adjusts above limits once per minute based on current sizes.
- if youngest is below the age ratio limit of oldest, move a page to it.
"""
# rotate windows
history['w'].append({})
if (len(history['w']) > args.window):
history['w'].pop(0)
w = history['w'][-1]
oldest = (-1, 0)
youngest = (-1, sys.maxsize)
too_free = False
# Most bytes free
decision = (-1, -1)
if int(stats['slab_global_page_pool']) < memfree[0] / 2:
w['slab_pool_low'] = 1
if int(stats['slab_global_page_pool']) > memfree[0]:
w['slab_pool_high'] = 1
if args.verbose:
print("global pool: [{}]".format(stats['slab_global_page_pool']))
pool_low = window_key_check(history, 'slab_pool_low')
for sid, slab in diffs.items():
small_slab = False
free_enough = False
# Only balance larger slab classes
if slab['chunk_size'] < args.size:
small_slab = True
w[sid] = {}
if 'evicted_d' not in slab or 'total_pages_d' not in slab:
continue
# mark this window as dirty if total pages increases or evictions
# happened
if slab['total_pages_d'] > 0:
w[sid]['dirty'] = 1
if slab['evicted_d'] > 0:
w[sid]['dirty'] = 1
w[sid]['ev'] = 1
if slab['free_chunks'] > memfree[sid]:
free_enough = True
if memfree[sid] > 0 and slab['free_chunks'] > (memfree[sid] * 2):
w[sid]['excess_free'] = 1
w[sid]['age'] = slab['age']
age = window_check(history, sid, 'age') / len(history['w'])
# if > 2.5 pages free, and not dirty, reassign to global page pool
if slab['free_chunks'] > slab['chunks_per_page'] * MIN_PAGES_FOR_RECLAIM and too_free == False:
dirt = window_check(history, sid, 'dirty')
excess = window_check(history, sid, 'excess_free')
if small_slab == True and dirt == 0:
# If we're a small slab, don't hang on to free memory forever.
decision = (sid, 0)
too_free = True
elif small_slab == False and dirt == 0 \
and excess >= len(history['w']):
decision = (sid, 0)
too_free = True
# are we the oldest slab class? (and a valid target)
# don't consider for young if we've recently given it unused memory
if small_slab == False:
if age > oldest[1] and slab['total_pages'] > MIN_PAGES_FOR_SOURCE:
oldest = (sid, age)
if age < youngest[1] and slab['total_pages'] > 0 \
and window_check(history, sid, 'excess_free') < len(history['w']) \
and not (window_check(history, sid, 'relaxed') and free_enough):
youngest = (sid, age)
if w.get('slab_pool_high') and youngest[0] != -1:
# if global pool is too high, feed youngest large class.
if slab['free_chunks'] <= memfree[youngest[0]]:
decision = (0, youngest[0])
w[youngest[0]]['relaxed'] = 1
elif too_free == False and pool_low and oldest[0] != -1:
# if pool is too low, take from oldest large class.
if args.verbose:
print("oldest: [class: {}] [age: {:.2f}]".format(int(oldest[0]), oldest[1]))
decision = (oldest[0], 0)
elif too_free == False and youngest[0] != -1 and oldest[0] != -1 and youngest[0] != oldest[0]:
# youngest is outside of the tolerance ratio, move a page around.
if args.verbose:
print("old: [class: {}] [age: {:.2f}]\nyoung: [class: {}] [age: {:.2f}]".format(
int(oldest[0]), oldest[1], int(youngest[0]), youngest[1]))
slab = diffs[youngest[0]]
#print("F:{} L:{} Y:{} R:{}".format(slab['free_chunks'], memfree[youngest[0]], int(youngest[1]), int(oldest[1] * args.ratio)))
if youngest[1] < oldest[1] * args.ratio:
w[youngest[0]]['relaxed'] = 1
if slab['free_chunks'] <= memfree[youngest[0]]:
decision = (0, youngest[0])
if (len(history['w']) >= args.window):
return decision
return (-1, -1)
def run_move(s, decision):
s.write("slabs reassign " + str(decision[0]) + " " + str(decision[1]) + "\r\n")
line = s.readline().rstrip()
if args.verbose:
print("move result:", line)
def diff_stats(before, after):
""" fills out "diffs" as deltas between before/after,
and "totals" as the sum of all slab classes.
"_d" postfix to keys means the delta between before/after.
non-postfix keys are total as of 'after's reading.
"""
diffs = {}
totals = {}
for slabid in after.keys():
sb = before.get(slabid)
sa = after.get(slabid)
if not (sb and sa):
continue
slab = sa.copy()
for k in sa.keys():
if k not in sb:
continue
if k not in totals:
totals[k] = 0
totals[k + '_d'] = 0
if k + '_d' not in slab:
slab[k + '_d'] = 0
if re.search(r"^\d+$", sa[k]):
totals[k] += int(sa[k])
slab[k] = int(sa[k])
slab[k + '_d'] = int(sa[k]) - int(sb[k])
totals[k + '_d'] += int(sa[k]) - int(sb[k])
slab['slab'] = slabid
diffs[slabid] = slab
return (diffs, totals)
def read_slab_stats(s):
slabs = {}
for statcmd in ['items', 'slabs']:
#print("stat cmd: " + statcmd)
# FIXME: Formatting
s.write("stats " + statcmd + "\r\n")
while True:
line = s.readline().rstrip()
if line.startswith("END"):
break
m = re.match(r"^STAT (?:items:)?(\d+):(\S+) (\S+)", line)
if m:
(slab, var, val) = m.groups()
if slab not in slabs:
slabs[slab] = {}
slabs[slab][var] = val
#print("line: " + line)
return slabs
# HACK: lets look at 'evictions' being nonzero to indicate memory filled at some point.
def read_stats(s):
stats = {}
s.write("stats\r\n")
while True:
line = s.readline().rstrip()
if line.startswith("END"):
break
m = re.match(r"^STAT (\S+) (\S+)", line)
if m:
(key, val) = m.groups()
stats[key] = val
return stats
def pct(num, divisor):
if not divisor:
return 0
return (num / divisor)
def show_detail(diffs, totals):
""" just a pretty printer for some extra data """
print("\n {:2s}: {:8s} (pct ) {:10s} (pct ) {:6s} (pct) {:6s}".format('sb',
'evicted', 'items', 'pages', 'age'))
for sid, slab in diffs.items():
if 'evicted_d' not in slab:
continue
print(" {:2d}: {:8d} ({:.2f}%) {:10d} ({:.4f}%) {:6d} ({:.2f}%) {:6d}".format(
int(sid), slab['evicted_d'], pct(slab['evicted_d'], totals['evicted_d']),
slab['number'], pct(slab['number'], totals['number']),
slab['total_pages'], pct(slab['total_pages'],
totals['total_pages']),
slab['age']))
def memfree_check(s, diffs, totals):
info = {}
# manage about this many free chunks in each slab class.
for sid, slab in diffs.items():
if sid == 0:
continue
hold_free = int((slab['used_chunks'] + slab['free_chunks']) * args.free)
# Hold a minimum of 1.5 pages so page moves are unlikely to lose items.
if slab['chunks_per_page'] * MIN_PAGES_FREE > hold_free:
hold_free = int(slab['chunks_per_page'] * MIN_PAGES_FREE)
info[sid] = hold_free
# TODO: only adjust if different?
s.write("extstore free_memchunks {} {}\r\n".format(sid, hold_free))
s.readline()
# how many pages to leave in the global pool.
info[0] = int(totals['total_pages'] * args.free)
return info
stats_pre = {}
history = { 'w': [{}] }
memfree = { 0: 2 }
last_memfree_check = 0
while True:
try:
with socket.create_connection((host, port), 5) as c:
s = c.makefile(mode="rw", buffering=1)
s.write("slabs automove 0\r\n")
print(s.readline().rstrip())
while True:
stats_post = read_slab_stats(s)
stats = read_stats(s)
(diffs, totals) = diff_stats(stats_pre, stats_post)
#if args.verbose:
# show_detail(diffs, totals)
if int(stats['evictions']) > 0:
if (last_memfree_check < time() - 60) and totals.get('total_pages'):
memfree = memfree_check(s, diffs, totals)
last_memfree_check = time()
decision = (-1, -1)
decision = determine_move(history, stats, diffs, memfree)
if int(decision[0]) > 0 and int(decision[1]) >= 0:
print("moving page from, to:", decision)
if args.automove:
run_move(s, decision)
# Minimize sleeping if we just moved a page to global pool.
# Improves responsiveness during flushes/quick changes.
if decision[1] == 0:
continue
else:
sleep(args.sleep)
stats_pre = stats_post
except:
err = sys.exc_info()
print("disconnected:", err[0], err[1])
traceback.print_exc()
stats_pre = {}
history = { 'w': [{}] }
sleep(args.sleep)