Re: Maybe consider rpmalloc

[Jon Turney <jon.turney@dronecode.org.uk>]

On 14/04/2021 09:19, Mark Geisert wrote:
> Teemu Nätkinniemi wrote:
>> Thanks a lot for looking into this issue! I wonder if there are any
>> other applications affected by this?
> 
> We have several examples by now.  All are (relatively) long-lasting 
> apps, with high to very high memory allocation churn, often 
> multi-threaded.  I believe some specific rsync operations hit this.  
> Achim reported a zstd operation that exhibited the symptoms.  And I've 
> been attempting to get a working replacement for Cygwin's malloc for 
> some time but every malloc I've tested, several of them, exhibits 
> similar symptoms: excessive time being spent in ntdll.dll presumably 
> supporting the memory operations.
> 
> Your rpmalloc "hack" is interesting in that you aren't using Cygwin's 
> mmap() underneath the malloc routines; you're calling Windows VM ops 
> directly.  Not sure yet what all the implications are.
> 
> I need to identify what's being hit within ntdll.dll.  Is it one or two 
> routines, or just hot locks.  So that means getting the correct PDB file 
> from the MS Symbol Server and working with Windows tools I'm unfamiliar 
> with.  Sigh, in an earlier life I had a gdb that we'd taught how to work 

Yes, this would indeed be a very useful thing to have in gdb.

I'm not aware of any public work in that direction, though.

> with PDB files; dunno if I could resurrect that.  Profiling the Cygwin 
> DLL itself, call profiling I mean, might lead somewhere as well.

In the past I've had some success with using the Very Sleepy profiler 
([1]), which can use both PDB and DWARF symbols, on cygwin executables.

[1] https://github.com/VerySleepy/verysleepy