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Server Memory - BuildStuff Ukraine 2019
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Андрей Листочкин (Andrey Listochkin)
November 18, 2019
Programming
0
23
Server Memory - BuildStuff Ukraine 2019
Андрей Листочкин (Andrey Listochkin)
November 18, 2019
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Transcript
None
@listochkin + fb.com/tektonna
Memory Management
A bit deeper than most talks on similar subject
None
CPU Caches RAM Swap Disk Network
Operating System
None
Pages 4k
Virtual
3 processes [0 … ∞] [0 … ∞] [0 …
∞]
Allocate page But not really
None
malloc calloc realloc
None
pointer = malloc(size)
free(pointer)
malloc malloc malloc free malloc free free
Forget to free Free the wrong pointer Read from unallocated
memory
Can we do better?
Reference Counting
None
const players = [ … ] players.forEach(p => makeMove(p))
a = … doX(a) yield a
if ( … ) { let a = … …
}
C++: std::shared_ptr
None
Optimizations
Delayed Counting
Don’t count local references
function (user) { let email = user.email; … … }
Delayed deallocation
Reference Cycles
None
None
Compile time ref-counting
Several types of pointers
Ownership
Forbids cycles by forbidding several owning references at the same
time
None
None
None
Perl 1987 - today Python 1991 - 2001 PHP 1994
- 2009
Multiprocess deploys
fork
Copy on Write
Worker Accepts requests As memory use raises: Stop accepting requests
Complete in-flight requests Terminate
Master Keep track on workers Start new workers Signal them
to terminate when memory pressure is high
“Pre-fork”
Load the framework Load app code Run full GC ----
Start forking process to accept requests
None
None
“Processes” Supervision Trees
Tracing GC
1959 60 years ago
Start at Root references Follow all references Build a live
objects tree Delete all objects not part of the tree
Ruby Java JavaScript Lua Go Default Choice
Roots?
Constants Global variables Local variables Closures Thread-locals ...
Mark & Sweep vs Mark-Compact
None
Team Sweep: Go Ruby* Lua Embedded JS engines Erlang
Pros: Pointers don’t change Native extensions Easier to implement
Team Compact: Java JavaScript Ruby* Haskell
Pros: Less memory fragmentation over time Cons: Harder Takes longer
to do a GC
Incremental Marking
3-colored algorithm by Dijkstra™
None
None
None
None
None
What is a barrier? if statement
CPU branch predictor
Parallel marking
None
Lazy Sweep
Generational
Temporary data data.filter( … ).map( … ) log(`… ${data}`) JSON.stringify(result)
Major vs Minor GC
Pointers from Old objects to new objects
Remembered Set
Major GC Scan roots only Bigger object graph
Minor GC Scan roots + RS Small object graph
None
Modern GCs are hybrid
None
None
C-extensions
Can’t move objects if their references are passed to an
extension
Can’t add WB
RGen GC
2 types of objects WB-protected WB-unprotected
WBu are never OldGen
OldGen -> WBu WBu to Remembered Set
Mark WBus on every minor GC
Adding compaction for WBp
None
V8
Minor GC Parallel
Major Parallel marking Parallel / Concurrent Compact || Sweep
None
When to trigger GC?
Out-of-Bounds GC
Firefox Run GC in background tabs first instead of current
tab
Chrome Animation frame
OS Pages pre-forked processes malloc zones GC Regions Remembered Sets
Barriers
None
None
Practical Advice
Memory Leaks Multiprocess Deploys
Throughput ⇔ Latency
Throughput Batch jobs Queues
Latency Requests Messaging
Keep different types of workloads in different processes
More memory Swap with SSDs
Experiment and measure
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