* [Caml-list] Re: Memory fragmentation
2012-04-20 15:12 ` [Caml-list] Memory fragmentation SerP
@ 2012-04-20 15:27 ` SerP
2012-04-20 16:41 ` [Caml-list] " Török Edwin
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: SerP @ 2012-04-20 15:27 UTC (permalink / raw)
To: caml-list
[-- Attachment #1: Type: text/plain, Size: 1352 bytes --]
Ocaml 3.12.0., Lwt 2.3.1
On Apr 20, 2012 7:12 PM, "SerP" <serp256@gmail.com> wrote:
> Hi!
> We have developped a daemon on ocaml using the lwt lib(libev). It
> processes about 800 requests per second, but it increases to 2 Gb in memory
> for a hour of work. We have studied the problem for a long time, using
> mtrace, mallinfo and other tools, and we tried to change GC params. We
> found out that setting up GC.minor_heap_size=10Mb а
> major_heap_increment=2Мb will make the daemon grow slower. mallinfо shows
> that the memory (1,5G) is allocated using mmap (blkhd field in mallinfo
> struct) and arena size - about 20M In this case, first calls of GC.compact
> compress the daemon to 200 Mb (live -110Mb) , and mallinfo show decreasing
> of total size of memory allocated by mmap. The daemon keeps growing, but it
> allocates the memory to arena (using brk), and calls of GC.compact leads to
> decrease of heap_bytes to 200M, but arena size (1.5 Gb) does not decrease,
> just doing less uordblks and more fordblks (fileds I.e., after first calls
> of GC.compact, the daemon starts using brk much more than mmap, and cant
> memory given back to the system.
>
> If Gc.allocation_policy is first fit, memory usage is stable, and it's
> grow very little, but worked very slowly.
>
> Any suggestions are very welcome. Thanks
>
[-- Attachment #2: Type: text/html, Size: 1576 bytes --]
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [Caml-list] Memory fragmentation
2012-04-20 15:12 ` [Caml-list] Memory fragmentation SerP
2012-04-20 15:27 ` [Caml-list] " SerP
@ 2012-04-20 16:41 ` Török Edwin
2012-04-20 18:32 ` SerP
2012-04-20 21:32 ` ygrek
2012-04-21 7:26 ` rixed
3 siblings, 1 reply; 7+ messages in thread
From: Török Edwin @ 2012-04-20 16:41 UTC (permalink / raw)
To: caml-list
On 04/20/2012 06:12 PM, SerP wrote:
> Hi!
> We have developped a daemon on ocaml using the lwt lib(libev). It processes about 800 requests per second, but it increases to 2 Gb in memory for a hour of work. We have studied the problem for a long
> time, using mtrace, mallinfo and other tools,
> and we tried to change GC params. We found out that setting up GC.minor_heap_size=10Mb а major_heap_increment=2Мb will make the daemon grow slower.
> mallinfо shows that the memory (1,5G) is allocated using mmap (blkhd field in mallinfo struct) and arena size - about 20M In this case, first calls of GC.compact compress the daemon to 200 Mb (live
> -110Mb) , and mallinfo show decreasing of total size of memory allocated by mmap. The daemon keeps growing, but it allocates the memory to arena (using brk), and calls of GC.compact leads to decrease
> of heap_bytes to 200M, but arena size (1.5 Gb) does not decrease, just doing less uordblks and more fordblks (fileds I.e., after first calls of GC.compact, the daemon starts using brk much more than
> mmap, and cant memory given back to the system.
Sounds like a fragmentation problem in glibc's heap that causes increased VIRT usage.
IIRC glibc has a default threshold of 128k for deciding to use brk() vs mmap(), and OCaml's default major_heap_increment (124k) is just below that,
which would explain the behaviour you see, and also explain why using a larger major_heap_increment (2M) improves the situation:
brk() cannot free "holes", while mmap arenas can.
You can use malloc_stats() to check whether OCaml gives back all memory to glibc or not, and you can try to use
an alternative malloc implementation (like jemalloc) that might cope better with fragmentation.
However this doesn't explain why memory keeps growing after a Gc.compact, unless calls to malloc
are mixed between the OCaml runtime, Lwt and libev. If that is the case then maybe it would help
to try and allocate memory in the OCaml's runtime by using mmap() directly.
Is your application completely single-threaded (since you're using lwt), or do you also use multiple threads?
I think that glibc caches mmap-ed areas even if you free them (i.e. they're still mapped into your process
but they might be changed via mprotect() to PROT_NONE), which is especially a problem if you use multiple threads.
Best regards,
--Edwin
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [Caml-list] Memory fragmentation
2012-04-20 15:12 ` [Caml-list] Memory fragmentation SerP
2012-04-20 15:27 ` [Caml-list] " SerP
2012-04-20 16:41 ` [Caml-list] " Török Edwin
@ 2012-04-20 21:32 ` ygrek
2012-04-21 7:26 ` rixed
3 siblings, 0 replies; 7+ messages in thread
From: ygrek @ 2012-04-20 21:32 UTC (permalink / raw)
To: caml-list
On Fri, 20 Apr 2012 19:12:12 +0400
SerP <serp256@gmail.com> wrote:
> Hi!
> We have developped a daemon on ocaml using the lwt lib(libev). It processes
> about 800 requests per second, but it increases to 2 Gb in memory for a
> hour of work. We have studied the problem for a long time, using mtrace,
> mallinfo and other tools, and we tried to change GC params. We found out
> that setting up GC.minor_heap_size=10Mb а major_heap_increment=2Мb will
> make the daemon grow slower. mallinfо shows that the memory (1,5G) is
> allocated using mmap (blkhd field in mallinfo struct) and arena size -
> about 20M In this case, first calls of GC.compact compress the daemon to
> 200 Mb (live -110Mb) , and mallinfo show decreasing of total size of memory
> allocated by mmap. The daemon keeps growing, but it allocates the memory to
> arena (using brk), and calls of GC.compact leads to decrease of heap_bytes
> to 200M, but arena size (1.5 Gb) does not decrease, just doing less
> uordblks and more fordblks (fileds I.e., after first calls of GC.compact,
> the daemon starts using brk much more than mmap, and cant memory given back
> to the system.
Alternative malloc implementation may well be worth a try. I've seen the cases
when glibc was constantly growing RSS while tcmalloc was on stable level (and 10x less),
guessing due to fragmentation.
Maybe related, see PR#5389 for ocaml compaction related issues.
Also have a look at http://ygrek.org.ua/p/code/mlvalues.py for the way to peep
into ocaml heap at runtime.
--
ygrek
http://ygrek.org.ua
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [Caml-list] Memory fragmentation
2012-04-20 15:12 ` [Caml-list] Memory fragmentation SerP
` (2 preceding siblings ...)
2012-04-20 21:32 ` ygrek
@ 2012-04-21 7:26 ` rixed
2012-04-24 19:24 ` SerP
3 siblings, 1 reply; 7+ messages in thread
From: rixed @ 2012-04-21 7:26 UTC (permalink / raw)
To: caml-list
There is a commit dating from a few days ago that might
be related to your problem (commit msg was :
PR#5389: compaction sometimes leaves a very large heap)
^ permalink raw reply [flat|nested] 7+ messages in thread