[pbs-devel] [PATCH 0/9] Improve live-restore speed and replace AsyncIndexReader

[Stefan Reiter]

This series is the third attempt[0] at substantially improving live-restore
performance. This time, a fully async- and concurrency safe LRU cache is
implemented, and a new CachedChunkReader is used to provide lock-free reading
from a remote chunk source. The big performance improvements come from removing
the global Mutex synchronising all read_image_at requests in the QEMU library
and the shared LRU cache.

The idea of using 'mmap' to alleviate memory pressure was dropped in favor of
using a shared cache between drives. This provides about the same performance
improvement in typical live-restore scenarios, but with a fixed memory
requirement, independant of drives. Adding 'mmap' caching is doable, but the
Rust code really doesn't look very nice with it, and I think it's not necessary
in this version...

Anyway, I figured out how to better benchmark the changes too, and can now
reproduce the performance gains very reliably. Below is a (gnu)plot of running
40 live-restores of a Windows 10 VM with a single 32GB disk, first with the
currently shipping libproxmox-backup-qemu0 (A) and then with the patched one
from this series (B). Testing was done with QEMU 6.0.


 seconds
 240 +-----------------------------------------------------------------------+
     |        +        +        +        +        +        +   A    +        |
 230 |-+                               A        A A                        +-|
     |   A  A A            AA       A                  A     A  A            |
 220 |-+        A AA              A        A                               +-|
     |    A          A   A    A A    A       AA       A             A        |
 210 |-+               A                            A      A      A   A  A A-|
     |                                                                  A    |
 200 |-+                                 A                                 +-|
     |                                                                       |
 190 |-+                                                                   +-|
     |                                                                       |
 180 |-A                                                                   +-|
     |                                                                       |
 170 |-+                                                                   +-|
     |                            B                             B   B        |
 160 |-B                    B   B      B B          B    B                 +-|
     |                   B    B               B                   B     B    |
 150 |-+ BB   B   BB B     B        B      B          B    B          B    B-|
     |      B + B      +        +    B   +   B  B +    B   + B B    +    B   |
 140 +-----------------------------------------------------------------------+
     0        5        10       15       20       25       30       35       40
                                     iteration
     1.0.3-1    A
     patched    B


[0] see: https://lists.proxmox.com/pipermail/pbs-devel/2021-April/002932.html


proxmox-backup: Stefan Reiter (7):
  tools/BroadcastFuture: add testcase for better understanding
  tools: add AsyncLruCache as a wrapper around sync LruCache
  backup: add CachedChunkReader utilizing AsyncLruCache
  backup: add AsyncRead/Seek to CachedChunkReader
  replace AsyncIndexReader with SeekableCachedChunkReader
  backup: remove AsyncIndexReader
  tools/lru_cache: make minimum capacity 1

 src/api2/admin/datastore.rs            |   4 +-
 src/backup.rs                          |   4 +-
 src/backup/async_index_reader.rs       | 215 -------------------------
 src/backup/cached_chunk_reader.rs      | 199 +++++++++++++++++++++++
 src/bin/proxmox_backup_client/mount.rs |   4 +-
 src/tools.rs                           |   1 +
 src/tools/async_lru_cache.rs           | 135 ++++++++++++++++
 src/tools/broadcast_future.rs          |  11 ++
 src/tools/lru_cache.rs                 |   1 +
 9 files changed, 353 insertions(+), 221 deletions(-)
 delete mode 100644 src/backup/async_index_reader.rs
 create mode 100644 src/backup/cached_chunk_reader.rs
 create mode 100644 src/tools/async_lru_cache.rs

proxmox-backup-qemu: Stefan Reiter (2):
  add shared_cache module
  access: use CachedChunkReader

 src/lib.rs          |  7 ++++++-
 src/restore.rs      | 30 ++++++++----------------------
 src/shared_cache.rs | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 23 deletions(-)
 create mode 100644 src/shared_cache.rs

-- 
2.30.2