diff options
Diffstat (limited to '0103-tools-ocaml-GC-parameter-tuning.patch')
| -rw-r--r-- | 0103-tools-ocaml-GC-parameter-tuning.patch | 126 |
1 files changed, 0 insertions, 126 deletions
diff --git a/0103-tools-ocaml-GC-parameter-tuning.patch b/0103-tools-ocaml-GC-parameter-tuning.patch deleted file mode 100644 index d1473df..0000000 --- a/0103-tools-ocaml-GC-parameter-tuning.patch +++ /dev/null @@ -1,126 +0,0 @@ -From 9f89883fabd53cb7873cc31778887ba2a1228dd8 Mon Sep 17 00:00:00 2001 -From: =?UTF-8?q?Edwin=20T=C3=B6r=C3=B6k?= <edvin.torok@citrix.com> -Date: Wed, 12 Oct 2022 19:13:07 +0100 -Subject: [PATCH 103/126] tools/ocaml: GC parameter tuning -MIME-Version: 1.0 -Content-Type: text/plain; charset=UTF-8 -Content-Transfer-Encoding: 8bit - -By default the OCaml garbage collector would return memory to the OS only -after unused memory is 5x live memory. Tweak this to 120% instead, which -would match the major GC speed. - -This is part of XSA-326. - -Signed-off-by: Edwin Török <edvin.torok@citrix.com> -Acked-by: Christian Lindig <christian.lindig@citrix.com> -(cherry picked from commit 4a8bacff20b857ca0d628ef5525877ade11f2a42) ---- - tools/ocaml/xenstored/define.ml | 1 + - tools/ocaml/xenstored/xenstored.ml | 64 ++++++++++++++++++++++++++++++ - 2 files changed, 65 insertions(+) - -diff --git a/tools/ocaml/xenstored/define.ml b/tools/ocaml/xenstored/define.ml -index 6b06f808595b..ba63a8147e09 100644 ---- a/tools/ocaml/xenstored/define.ml -+++ b/tools/ocaml/xenstored/define.ml -@@ -25,6 +25,7 @@ let maxwatch = ref (100) - let maxtransaction = ref (10) - let maxrequests = ref (1024) (* maximum requests per transaction *) - -+let gc_max_overhead = ref 120 (* 120% see comment in xenstored.ml *) - let conflict_burst_limit = ref 5.0 - let conflict_max_history_seconds = ref 0.05 - let conflict_rate_limit_is_aggregate = ref true -diff --git a/tools/ocaml/xenstored/xenstored.ml b/tools/ocaml/xenstored/xenstored.ml -index d44ae673c42a..3b57ad016dfb 100644 ---- a/tools/ocaml/xenstored/xenstored.ml -+++ b/tools/ocaml/xenstored/xenstored.ml -@@ -104,6 +104,7 @@ let parse_config filename = - ("quota-maxsize", Config.Set_int Quota.maxsize); - ("quota-maxrequests", Config.Set_int Define.maxrequests); - ("quota-path-max", Config.Set_int Define.path_max); -+ ("gc-max-overhead", Config.Set_int Define.gc_max_overhead); - ("test-eagain", Config.Set_bool Transaction.test_eagain); - ("persistent", Config.Set_bool Disk.enable); - ("xenstored-log-file", Config.String Logging.set_xenstored_log_destination); -@@ -265,6 +266,67 @@ let to_file store cons fds file = - (fun () -> close_out channel) - end - -+(* -+ By default OCaml's GC only returns memory to the OS when it exceeds a -+ configurable 'max overhead' setting. -+ The default is 500%, that is 5/6th of the OCaml heap needs to be free -+ and only 1/6th live for a compaction to be triggerred that would -+ release memory back to the OS. -+ If the limit is not hit then the OCaml process can reuse that memory -+ for its own purposes, but other processes won't be able to use it. -+ -+ There is also a 'space overhead' setting that controls how much work -+ each major GC slice does, and by default aims at having no more than -+ 80% or 120% (depending on version) garbage values compared to live -+ values. -+ This doesn't have as much relevance to memory returned to the OS as -+ long as space_overhead <= max_overhead, because compaction is only -+ triggerred at the end of major GC cycles. -+ -+ The defaults are too large once the program starts using ~100MiB of -+ memory, at which point ~500MiB would be unavailable to other processes -+ (which would be fine if this was the main process in this VM, but it is -+ not). -+ -+ Max overhead can also be set to 0, however this is for testing purposes -+ only (setting it lower than 'space overhead' wouldn't help because the -+ major GC wouldn't run fast enough, and compaction does have a -+ performance cost: we can only compact contiguous regions, so memory has -+ to be moved around). -+ -+ Max overhead controls how often the heap is compacted, which is useful -+ if there are burst of activity followed by long periods of idle state, -+ or if a domain quits, etc. Compaction returns memory to the OS. -+ -+ wasted = live * space_overhead / 100 -+ -+ For globally overriding the GC settings one can use OCAMLRUNPARAM, -+ however we provide a config file override to be consistent with other -+ oxenstored settings. -+ -+ One might want to dynamically adjust the overhead setting based on used -+ memory, i.e. to use a fixed upper bound in bytes, not percentage. However -+ measurements show that such adjustments increase GC overhead massively, -+ while still not guaranteeing that memory is returned any more quickly -+ than with a percentage based setting. -+ -+ The allocation policy could also be tweaked, e.g. first fit would reduce -+ fragmentation and thus memory usage, but the documentation warns that it -+ can be sensibly slower, and indeed one of our own testcases can trigger -+ such a corner case where it is multiple times slower, so it is best to keep -+ the default allocation policy (next-fit/best-fit depending on version). -+ -+ There are other tweaks that can be attempted in the future, e.g. setting -+ 'ulimit -v' to 75% of RAM, however getting the kernel to actually return -+ NULL from allocations is difficult even with that setting, and without a -+ NULL the emergency GC won't be triggerred. -+ Perhaps cgroup limits could help, but for now tweak the safest only. -+*) -+ -+let tweak_gc () = -+ Gc.set { (Gc.get ()) with Gc.max_overhead = !Define.gc_max_overhead } -+ -+ - let _ = - let cf = do_argv in - let pidfile = -@@ -274,6 +336,8 @@ let _ = - default_pidfile - in - -+ tweak_gc (); -+ - (try - Unixext.mkdir_rec (Filename.dirname pidfile) 0o755 - with _ -> --- -2.37.4 - |