[Webkit-unassigned] [Bug 118733] Javascript JIT still allocates 2GB of memory on x86-64 Linux

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Tue Jul 16 08:53:51 PDT 2013


Oliver Hunt <oliver at apple.com> changed:

           What    |Removed                     |Added
                 CC|                            |oliver at apple.com

--- Comment #2 from Oliver Hunt <oliver at apple.com>  2013-07-16 08:54:00 PST ---
(In reply to comment #0)
> Created an attachment (id=206778)
 --> (https://bugs.webkit.org/attachment.cgi?id=206778&action=review) [details]
> Use MAP_32BIT
> See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=712387 for the original bugreport.
> Currently the javascript JIT allocates 2GB on x86-64, to ensure that all jumps are within a 2GB range.
> This causes problems without overcommit (or without a swapfile), even on a machine with 8GB of physical RAM.
> Attached is a patch that uses MAP_32BIT, instead of the wasteful allocation of 2GB.

It doesn't use 2gig of memory, it reserves 2gig of address space.  I would be stunned if linux cannot handle reserving address space as that's a common technique used by garbage collectors.

32Mb is also vastly too small to successfully jit large pieces of JS so i'll assume that there were no perf tests run on this patch either.

I think the correct fix here is to find out how linux GCs reserve address space without having the VM allocate physical backing memory.

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