Last Comment Bug 811740 - Reduce the maximum amount of unused dirty pages kept by jemalloc
: Reduce the maximum amount of unused dirty pages kept by jemalloc
Status: RESOLVED FIXED
[MemShrink:P2]
:
Product: Firefox OS
Classification: Client Software
Component: General (show other bugs)
: unspecified
: All Gonk (Firefox OS)
: -- normal (vote)
: B2G C2 (20nov-10dec)
Assigned To: Gabriele Svelto [:gsvelto]
:
Mentors:
Depends on:
Blocks: slim-fast
  Show dependency treegraph
 
Reported: 2012-11-14 08:12 PST by Gabriele Svelto [:gsvelto]
Modified: 2012-12-21 15:21 PST (History)
13 users (show)
See Also:
Crash Signature:
(edit)
QA Whiteboard:
Iteration: ---
Points: ---
fixed
fixed


Attachments
Memory report using a 1MiB limit for dirty pages (71.48 KB, application/x-gzip)
2012-11-20 14:35 PST, Gabriele Svelto [:gsvelto]
no flags Details
Memory report using a 2MiB limit for dirty pages (71.36 KB, application/x-gzip)
2012-11-20 14:36 PST, Gabriele Svelto [:gsvelto]
no flags Details
Memory report using a 4MiB limit for dirty pages (71.46 KB, application/x-gzip)
2012-11-20 14:37 PST, Gabriele Svelto [:gsvelto]
no flags Details
Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G (1.66 KB, patch)
2012-11-26 08:44 PST, Gabriele Svelto [:gsvelto]
justin.lebar+bug: feedback+
Details | Diff | Splinter Review
[PATCH v2] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G (2.04 KB, patch)
2012-11-26 14:08 PST, Gabriele Svelto [:gsvelto]
justin.lebar+bug: review+
mh+mozilla: review-
Details | Diff | Splinter Review
[PATCH v3] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G (1.67 KB, patch)
2012-11-28 08:06 PST, Gabriele Svelto [:gsvelto]
justin.lebar+bug: review+
mh+mozilla: review+
justin.lebar+bug: approval‑mozilla‑aurora+
justin.lebar+bug: approval‑mozilla‑beta+
Details | Diff | Splinter Review

Description Gabriele Svelto [:gsvelto] 2012-11-14 08:12:30 PST
When freeing memory jemalloc keeps a certain amount of dirty unused pages around in order to speed up future allocations. Since these pages have been already touched by the application they appear as in use to the kernel and cannot be reclaimed when memory is running low. We should evaluate the performance impact of reducing the maximum amount of these pages and if it is acceptable introduce a lower limit, see bug 805855.

Currently the maximum amount of dirty unused pages is set to 4 MiB per arena (in our case only one arena is present). The maximum can be reduced in mozjemalloc by adding 'f' characters to the options string either by setting the MALLOC_OPTIONS environment variable or by changing the _malloc_options string in jemalloc.c; for every 'f' added the maximum amount is halved (i.e. setting the string to "ff" will yield a 1 MiB maximum for example).

In jemalloc 3 this limit is dynamic and is set by default to be 1/32 of the arena size, the ratio can be changed by calling mallctl() with the "opt.lg_dirty_mult" parameter.
Comment 1 Gabriele Svelto [:gsvelto] 2012-11-20 14:35:55 PST
Created attachment 683745 [details]
Memory report using a 1MiB limit for dirty pages
Comment 2 Gabriele Svelto [:gsvelto] 2012-11-20 14:36:55 PST
Created attachment 683748 [details]
Memory report using a 2MiB limit for dirty pages
Comment 3 Gabriele Svelto [:gsvelto] 2012-11-20 14:37:31 PST
Created attachment 683749 [details]
Memory report using a 4MiB limit for dirty pages
Comment 4 Gabriele Svelto [:gsvelto] 2012-11-20 14:48:39 PST
I've attached some new reports on a current gecko/gaia combination now that many memory-saving patches have landed. The test consisted in booting the phone, letting it settle down, then launching the gallery app and letting it settle down too, to have a fairly large foreground application running that also provides repeatable behavior. A summary of the results can be found here (broken down by app and by maximum dirty pages limit).

Main process        4MiB      2MiB      1MiB
RSS                60.38     61.11     59.76
Heap-committed     30.85     30.16     28.88
Heap-dirty          2.53      1.16      0.58

Home screen        4MiB       2MiB      1MiB
RSS               24.13      23.92     24.18
Heap-committed      8.1       7.94      8.15
Heap-dirty            0       0.01      0.01

Gallery            4MiB       2MiB      1MiB
RSS               25.76      24.55     23.99
Heap-committed    10.11       8.79      8.35
Heap-dirty         1.87       0.57      0.27

Settings           4MiB       2MiB      1MiB
RSS               22.36      21.60     22.02
Heap-committed     7.02       6.61      6.82
Heap-dirty         0.03       0.03      0.04

Messages           4MiB       2MiB      1MiB
RSS               20.75      20.49     19.78
Heap-committed     6.71       6.22      5.55
Heap-dirty         1.62       1.13      0.46

Preallocated app   4MiB       2MiB      1MiB
RSS                4.02       4.02      4.02
Heap-committed     0.10       0.10      0.10
Heap-dirty        16.31      16.21     16.21

To summarize the results it seems that lowering the limit tends not only to save memory directly thanks to a lower number of dirty pages, but also improves the utilization of the committed heap space. This is probably due to less fragmentation in the existing partially used pages which the allocator is forced to pick up more often now that the free ones are more scarce.

Going from a 4 to a 1MiB limit in total we are looking at ~4MiB savings over a ~160MiB heap, a small but non-trivial number.

I wasn't yet able to gauge the performance impact of the change. Applications that should be impacted most would be ones with large swings in memory usage (they would trigger a larger number of mmap() and madvise() calls when using less dirty pages). However those large swings should not be happening due to the JS heap as that one is unaffected by this change.
Comment 5 Justin Lebar (not reading bugmail) 2012-11-23 13:20:21 PST
I ran SunSpider on my Otoro and saw no difference between 1mb and 4mb dirty page size.  (I'm hoping that SS is a reasonable benchmark to run on the phone, since it's much slower than a desktop.  I tried to run V8, but it took a /long/ time, and I wasn't patient enough to babysit it to keep the screen on, etc.)

Content processes often have less than 5mb of active heap, so having a 4mb dirty heap size is just silly.  Even in the main process, we're really not using a ton of heap space.

I'm in favor of reducing the dirty size to 1mb across the board.  We can always change it back.

What do you think, Gabriele?
Comment 6 Gabriele Svelto [:gsvelto] 2012-11-25 00:11:41 PST
(In reply to Justin Lebar [:jlebar] from comment #5)
> I ran SunSpider on my Otoro and saw no difference between 1mb and 4mb dirty
> page size.  (I'm hoping that SS is a reasonable benchmark to run on the
> phone, since it's much slower than a desktop.  I tried to run V8, but it
> took a /long/ time, and I wasn't patient enough to babysit it to keep the
> screen on, etc.)
> 
> Content processes often have less than 5mb of active heap, so having a 4mb
> dirty heap size is just silly.  Even in the main process, we're really not
> using a ton of heap space.

Indeed, jemalloc3 sets the amount of dirty pages to ~3% of the arena size so it would use 1MiB for a 32MiB arena. If the jemalloc designers were OK with this ratio then 4MiB is oversized for pretty much all of our processes.

> I'm in favor of reducing the dirty size to 1mb across the board.  We can
> always change it back.
> 
> What do you think, Gabriele?

I'm OK with doing it across the board. In future releases we'll probably start using jemalloc3 anyway and when we do this limit won't be used anymore.
Comment 7 Justin Lebar (not reading bugmail) 2012-11-26 07:43:14 PST
> I'm OK with doing it across the board.

Cool.  Can you post a patch?  I can review and merge it.
Comment 8 Gabriele Svelto [:gsvelto] 2012-11-26 08:44:16 PST
Created attachment 685189 [details] [diff] [review]
Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

I cooked up a patch quickly, I still have to test it so I'm not asking for the review just yet but I'd like you to take a look at its structure before going to the review stage.

I'm setting the _malloc_options variable to make sure this works on both the devices and on the desktop. I wanted to make it clear what the goal of the change were while avoiding putting an #ifdef around the _malloc_options variable.
Comment 9 Justin Lebar (not reading bugmail) 2012-11-26 10:11:59 PST
Comment on attachment 685189 [details] [diff] [review]
Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

Instead of doing an ifdef B2G here, could you add a configure-time variable MOZ_MALLOC_OPTIONS and AC_SUBST it?  That way, if Fennec wants this, they only need to set the same variable in configure.
Comment 10 Gabriele Svelto [:gsvelto] 2012-11-26 10:18:50 PST
(In reply to Justin Lebar [:jlebar] from comment #9)
> Instead of doing an ifdef B2G here, could you add a configure-time variable
> MOZ_MALLOC_OPTIONS and AC_SUBST it?  That way, if Fennec wants this, they
> only need to set the same variable in configure.

Sure, I didn't do it that way in the first place because I didn't want to ruin my ccache cache again ;-) I'll post an updated patch shortly.
Comment 11 Gabriele Svelto [:gsvelto] 2012-11-26 14:08:20 PST
Created attachment 685323 [details] [diff] [review]
[PATCH v2] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

Revised patch, I've moved MOZ_MALLOC_OPTIONS into configure.in, it gets set to the empty string when we set MOZ_MEMORY and is changed to "ff" when the B2G target is enabled. This enables it both on the devices and on the desktop. Finally the variable is added to mozilla-config.h via an AC_DEFINE_UNQUOTED() macro so anybody can change the variable in other places and have the desired string in place (e.g. for the Android builds for example).
Comment 12 Justin Lebar (not reading bugmail) 2012-11-26 14:10:56 PST
Comment on attachment 685323 [details] [diff] [review]
[PATCH v2] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

r=me, but I realize now we should get a build peer to sign off on it too, just in case I'm missing something.
Comment 13 Gabriele Svelto [:gsvelto] 2012-11-26 14:17:19 PST
(In reply to Justin Lebar [:jlebar] from comment #12)
> r=me, but I realize now we should get a build peer to sign off on it too,
> just in case I'm missing something.

Yep, I'm also not 100% sure I've got my definition in the right code-path. I've pushed it to try in the meantime:

https://tbpl.mozilla.org/?tree=Try&rev=68a17a42812a
Comment 14 Mozilla RelEng Bot 2012-11-26 16:45:39 PST
Try run for 68a17a42812a is complete.
Detailed breakdown of the results available here:
    https://tbpl.mozilla.org/?tree=Try&rev=68a17a42812a
Results (out of 17 total builds):
    success: 17
Builds (or logs if builds failed) available at:
http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/gsvelto@mozilla.com-68a17a42812a
Comment 15 Mike Hommey [:glandium] 2012-11-27 02:18:22 PST
Comment on attachment 685323 [details] [diff] [review]
[PATCH v2] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

Review of attachment 685323 [details] [diff] [review]:
-----------------------------------------------------------------

::: configure.in
@@ +7085,5 @@
>    esac
> +
> +  case "$MOZ_BUILD_APP" in
> +  b2g)
> +    MOZ_MALLOC_OPTIONS="ff" dnl Limit maximum dirty unused pages to 1MiB

I'm not particularly fond of putting that in configure.

Note this should also be adjusted for jemalloc3 (in memory/build/extraMallocFuncs.c or in memory/build/jemalloc_config.c after bug 804303)
Comment 16 Mike Hommey [:glandium] 2012-11-27 02:21:21 PST
(In reply to Mike Hommey [:glandium] from comment #15)
> I'm not particularly fond of putting that in configure.

That is, I prefer the previous approach.
Comment 17 Gabriele Svelto [:gsvelto] 2012-11-27 03:26:52 PST
(In reply to Mike Hommey [:glandium] from comment #15)
> Note this should also be adjusted for jemalloc3 (in
> memory/build/extraMallocFuncs.c or in memory/build/jemalloc_config.c after
> bug 804303)

You mean here?:

http://mxr.mozilla.org/mozilla-central/source/memory/build/extraMallocFuncs.c#130

In jemalloc3 the amount of dirty unused pages is computed differently, by default it's 1/32 of the arena size which is OK for us and I don't think will need further tweaking.

This is really just a stop-gap solution for reducing memory in B2G v1. Once jemalloc3 will be the default allocator this tweak will become obsolete just like the function I previously added to mozjemalloc to drop dirty pages.

> That is, I prefer the previous approach.

Either works for me, the first patch was less intrusive IMHO but modifying the configure script isn't a big deal either. Justin what do you think?
Comment 18 Justin Lebar (not reading bugmail) 2012-11-27 07:41:03 PST
(In reply to Mike Hommey [:glandium] from comment #16)
> (In reply to Mike Hommey [:glandium] from comment #15)
> > I'm not particularly fond of putting that in configure.
> 
> That is, I prefer the previous approach.

cjones enforces a policy of not having ifdef B2G in code anywhere that we can help it.  I don't really care; I'm just trying to enforce the rule consistently.
Comment 19 Justin Lebar (not reading bugmail) 2012-11-27 07:42:25 PST
Another option -- what I had in mind when I asked for this to go into configure -- is to add a configure option for "MOZ_REDUCE_JEMALLOC_DIRTY_SIZE" (or whatever), and enable that for B2G.  Would that be more palatable to you, Mike?
Comment 20 Mike Hommey [:glandium] 2012-11-27 07:47:11 PST
(In reply to Justin Lebar [:jlebar] from comment #18)
> cjones enforces a policy of not having ifdef B2G in code anywhere that we
> can help it.  I don't really care; I'm just trying to enforce the rule
> consistently.

I'm not convinced this rule is any helpful in the present case. In fact, I'm almost expecting platform-dependent values for malloc_options/je_malloc_conf (especially for mobile platforms).
Comment 21 Justin Lebar (not reading bugmail) 2012-11-27 08:16:34 PST
> In fact, I'm almost expecting platform-dependent values for 
> malloc_options/je_malloc_conf (especially for mobile platforms).

Sure, agreed.  I think the question is where should those platform-specific configuration values live: In code, or in configure?

Although I don't entirely agree with the policy, it does seem nicer to me in this case to have zero or one if define()'s in jemalloc.c, instead of explicitly listing every relevant platform in code, as

  if defined(B2G) || defined(ANDROID_FENNEC) || defined(MS_SURFACE) || ...

I think that's the general motivation behind Chris's policy.

But this patch is mostly a build patch, so I'm happy to let you make the call here on how you'd like to do this, irrespective of what Chris might or might not like.
Comment 22 Mike Hommey [:glandium] 2012-11-27 08:28:53 PST
(In reply to Justin Lebar [:jlebar] from comment #21)
> > In fact, I'm almost expecting platform-dependent values for 
> > malloc_options/je_malloc_conf (especially for mobile platforms).
> 
> Sure, agreed.  I think the question is where should those platform-specific
> configuration values live: In code, or in configure?
> 
> Although I don't entirely agree with the policy, it does seem nicer to me in
> this case to have zero or one if define()'s in jemalloc.c, instead of
> explicitly listing every relevant platform in code, as
> 
>   if defined(B2G) || defined(ANDROID_FENNEC) || defined(MS_SURFACE) || ...

I do think it's nice to group such processor boilerplate under a common umbrella in most cases, but I also think it's one of those few cases (along with architecture-specific things) where you don't want to do that.

(BTW, do you really want to enable this for B2G desktop?)
Comment 23 Gabriele Svelto [:gsvelto] 2012-11-27 08:37:56 PST
(In reply to Mike Hommey [:glandium] from comment #22)
> (BTW, do you really want to enable this for B2G desktop?)

The reason we want it to work on desktop too is to have consistent about:memory reports for application developers working on the desktop version. The idea is that whatever they get on the desktop should be as close as possible to the behavior on the device.
Comment 24 Mike Hommey [:glandium] 2012-11-27 08:43:45 PST
(In reply to Gabriele Svelto [:gsvelto] from comment #23)
> (In reply to Mike Hommey [:glandium] from comment #22)
> > (BTW, do you really want to enable this for B2G desktop?)
> 
> The reason we want it to work on desktop too is to have consistent
> about:memory reports for application developers working on the desktop
> version. The idea is that whatever they get on the desktop should be as
> close as possible to the behavior on the device.

I'm not convinced that will get you anywhere close, but ok.
Comment 25 Gabriele Svelto [:gsvelto] 2012-11-28 07:23:39 PST
I've slept on this and came up with another idea. What we want to do is to enable this particular memory optimization for devices that have a low amount of memory independently of the platform *or* application.

What I mean is that this particular optimization would be meaningful even for a Firefox desktop build running on a machine with 256-512MiB of memory; not a common configuration nowadays but still. Similarly we don't care about this if we're running on an Android device with 1GiB of memory, it could impact performance for no real benefit. BTW this kind of decision might also apply to other tweaks which involve a trade-off between absolute performance and memory consumption (memory cache sizes, aggressiveness when purging them, etc...).

So, instead of just hard-coding this option for certain platform/application combinations why don't we enable it depending on how much physical memory the host has? We already have the necessary functionality implemented in PR_GetPhysicalMemorySize() for every conceivable platform and we could just call it at the end of malloc_init_hard() and decide upon that if we want to limit the unused dirty pages or not. We're already doing something similar in the nsCacheService class:

http://mxr.mozilla.org/mozilla-central/source/netwerk/cache/nsCacheService.cpp#931
Comment 26 Mike Hommey [:glandium] 2012-11-28 07:29:00 PST
It's not possible to call a NSPR function from jemalloc.
Comment 27 Kartikaya Gupta (email:kats@mozilla.com) 2012-11-28 07:39:47 PST
(In reply to Gabriele Svelto [:gsvelto] from comment #25)
> So, instead of just hard-coding this option for certain platform/application
> combinations why don't we enable it depending on how much physical memory
> the host has? We already have the necessary functionality implemented in
> PR_GetPhysicalMemorySize() for every conceivable platform

Oh, interesting. Maybe I should have used that when I implemented isLowMemoryPlatform (bug 801818).
Comment 28 Gabriele Svelto [:gsvelto] 2012-11-28 07:40:19 PST
(In reply to Mike Hommey [:glandium] from comment #26)
> It's not possible to call a NSPR function from jemalloc.

Is this because there's no guarantee that they don't call malloc() themselves? Would it make sense to re-implement only the relevant bits? On Unixish environments we can query for the available physical memory by using sysconf() which is signal-safe and thus shouldn't be calling malloc() internally.
Comment 29 Gabriele Svelto [:gsvelto] 2012-11-28 07:41:26 PST
(In reply to Kartikaya Gupta (:kats) from comment #27)
> Oh, interesting. Maybe I should have used that when I implemented
> isLowMemoryPlatform (bug 801818).

Yes, it covers even the most obscure platforms so it should save you quite a bit of work.
Comment 30 Mike Hommey [:glandium] 2012-11-28 07:46:29 PST
(In reply to Gabriele Svelto [:gsvelto] from comment #28)
> (In reply to Mike Hommey [:glandium] from comment #26)
> > It's not possible to call a NSPR function from jemalloc.
> 
> Is this because there's no guarantee that they don't call malloc()
> themselves?

No, it's just not possible to have jemalloc (or anything else in libmozglue) depend on nspr on Linux and Android. (although i wouldn't be surprised if some static initializer in nspr calls malloc)
Comment 31 Justin Lebar (not reading bugmail) 2012-11-28 07:51:33 PST
I'm very happy to take the patch v1 which I rejected earlier.  We don't need a really complex fix here.
Comment 32 Gabriele Svelto [:gsvelto] 2012-11-28 08:06:15 PST
Created attachment 686113 [details] [diff] [review]
[PATCH v3] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

OK, I've refreshed the first patch and here it is, note that there was a type in the original as _malloc_options was set to "f" instead of "ff".
Comment 33 Gabriele Svelto [:gsvelto] 2012-11-28 09:40:28 PST
Pushed to try https://tbpl.mozilla.org/?tree=Try&rev=540bf50c9a47
Comment 34 Mozilla RelEng Bot 2012-11-28 12:15:34 PST
Try run for 540bf50c9a47 is complete.
Detailed breakdown of the results available here:
    https://tbpl.mozilla.org/?tree=Try&rev=540bf50c9a47
Results (out of 18 total builds):
    success: 17
    warnings: 1
Builds (or logs if builds failed) available at:
http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/gsvelto@mozilla.com-540bf50c9a47
Comment 35 Gabriele Svelto [:gsvelto] 2012-11-28 15:34:48 PST
It looks good except for a failed test that seems to be a known intermittent issue. I think it's good enough for checking in.
Comment 36 Ryan VanderMeulen [:RyanVM] 2012-11-28 19:50:09 PST
https://hg.mozilla.org/integration/mozilla-inbound/rev/4428aaa467a5
Comment 37 Justin Lebar (not reading bugmail) 2012-11-28 19:54:42 PST
Comment on attachment 686113 [details] [diff] [review]
[PATCH v3] Reduce the amount of unused dirty pages kept by jemalloc to 1MiB in B2G

a=me for branches (this is a b2g-only change, no risk to other platforms).
Comment 38 Justin Lebar (not reading bugmail) 2012-11-28 21:16:27 PST
Ryan, your scripts for finding patches needing checkin on branches will find this bug with a-a+ / a-b+, right?  I just don't want this bug to get lost.
Comment 39 Ryan VanderMeulen [:RyanVM] 2012-11-29 03:37:03 PST
yes, I look for fixed bugs with a+ and status flags not set
Comment 40 Ed Morley [:emorley] 2012-11-29 06:27:50 PST
https://hg.mozilla.org/mozilla-central/rev/4428aaa467a5
Comment 41 Ed Morley [:emorley] 2012-11-29 06:45:53 PST
https://hg.mozilla.org/mozilla-central/rev/4428aaa467a5
Comment 42 Chris Jones [:cjones] inactive; ni?/f?/r? if you need me 2012-12-07 23:36:07 PST
Oh golly, to think we could have left this on the table ... :/

Guys, RyanVM uplifts patches on his own time, and doesn't look for patches in Boot2Gecko because the volume of bb+ non-gecko stuff there is too high.  We need to
 (1) Ensure gecko work is filed in a gecko component
 (2) Put together some bugzilla queries to find patches like this which might have missed v1

Can someone own that please?

https://hg.mozilla.org/releases/mozilla-aurora/rev/e8c2cb8c583f
https://hg.mozilla.org/releases/mozilla-beta/rev/8b4170258440
Comment 43 Ryan VanderMeulen [:RyanVM] 2012-12-08 05:05:44 PST
I missed this one because I normally go off the Target Milestone flag (looking for mozilla20, mozilla19, etc). Thanks for pointing it out, I can make a new query for this.

(FWIW, what I do purposefully ignore is B2G::Gaia bb+ bugs since those at least in theory should be landing on Github - so make sure those are in the right component!)
Comment 44 Chris Jones [:cjones] inactive; ni?/f?/r? if you need me 2012-12-08 13:35:25 PST
This is not your problem at all.  I want to emphasize how much everyone appreciates the work you do :).
Comment 45 Mozilla RelEng Bot 2012-12-21 15:18:34 PST
Try run for 540bf50c9a47 is complete.
Detailed breakdown of the results available here:
    https://tbpl.mozilla.org/?tree=Try&rev=540bf50c9a47
Results (out of 19 total builds):
    success: 17
    warnings: 1
    failure: 1
Builds (or logs if builds failed) available at:
http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/gsvelto@mozilla.com-540bf50c9a47
Comment 46 Mozilla RelEng Bot 2012-12-21 15:21:43 PST
Try run for 68a17a42812a is complete.
Detailed breakdown of the results available here:
    https://tbpl.mozilla.org/?tree=Try&rev=68a17a42812a
Results (out of 18 total builds):
    success: 17
    failure: 1
Builds (or logs if builds failed) available at:
http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/gsvelto@mozilla.com-68a17a42812a

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