Possible memory leak?

[Peter Booth]

Perhaps I’m naive or just lucky, but I have used nginx on many contracts and permanent jobs for over ten years and have never attempted to reload canfigurations. I have always stopped then restarted nginx instances one at a time. Am I not recognizing a constraint that affects other people?

Curious ,

Peter

Sent from my iPhone

> On Mar 12, 2019, at 9:57 PM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> 
> Hello!
> 
>> On Tue, Mar 12, 2019 at 02:09:06PM -0400, wkbrad wrote:
>> 
>> First of all, thanks so much for your insights into this and being patient
>> with me.  :)  I'm just trying to understand the issue and what can be done
>> about it.
>> 
>> Can you explain to me what you mean by this?
>>> you can configure system allocator to use mmap()
>> 
>> I'm not a C programmer so correct me if I'm wrong, but doesn't the Nginx
>> code determine which memory allocator it uses?
> 
> Normally C programs use malloc() / free() functions as provided by 
> system libc library to allocate memory.  While it is possible for 
> an application to provide its own implementation of these 
> functions, this is something rarely used in practice.
> 
>> If not can you point me to an article that describes how to do that as I
>> would like to test it?
> 
> For details on how to control system allocator on Linux, please 
> refer to the mallopt(3) manpage, notably the 
> MALLOC_MMAP_THRESHOLD_ environment variable.  Web version is 
> available here:
> 
> http://man7.org/linux/man-pages/man3/mallopt.3.html
> 
> Please refer to the M_MMAP_THRESHOLD description in the same man 
> page for details on what it does and various implications.
> 
> Using a values less than NGX_CYCLE_POOL_SIZE (16k by default) 
> should help to move all configuration-related allocations into 
> mmap(), so these can be freed independently.  Alternatively, 
> recompiling nginx with NGX_CYCLE_POOL_SIZE set to a value larger 
> than 128k (default mmap() threshold) should have similar 
> effect.
> 
> Note though that there may be other limiting factors, 
> such as MALLOC_MMAP_MAX_, which limits maximum number of mmap() 
> allocations to 65536 by default.
> 
> You can also play with different allocators by using the 
> LD_PRELOAD environment variable, see for example jemalloc's wiki 
> here:
> 
> https://github.com/jemalloc/jemalloc/wiki/Getting-Started
> 
>> Also, you seem to be saying that Nginx IS attempting to free the memory but
>> is not able to due to the way the OS is allocating memory or refusing to
>> release the memory.  I've tested this in several Linux distros, kernels, and
>> Nginx versions and I see the same behavior in all of them.  Do you know of
>> an OS or specific distro where Nginx can release the old memory allocations
>> correctly?  I would like to test that too.  :)
> 
> Any Linux distro can be tuned so freed memory will be returned to 
> the system, see above.  And for example on FreeBSD, which uses 
> jemalloc as a system allocator, unused memory is properly returned 
> to the system out of the box (though can be seen in virtual 
> address space occupied by the process, since the allocator uses 
> madvise() to make the memory as unused instead of unmapping a 
> mapping).
> 
> -- 
> Maxim Dounin
> http://mdounin.ru/
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