Memory usage tweaks
There are some imgproxy options that can help you optimize memory usage and decrease memory fragmentation.
This is an advanced part. Please make sure that you know what you're doing before changing anything.
IMGPROXY_DOWNLOAD_BUFFER_SIZE
imgproxy uses memory buffers to download source images. While these buffers are empty at the beginning by default, they can grow to a required size when imgproxy downloads an image. Allocating new memory to grow the buffers can cause memory fragmentation. Allocating the required memory at the beginning can eliminate much of memory fragmentation since the buffers won't grow. Setting IMGPROXY_DOWNLOAD_BUFFER_SIZE will tell imgproxy to initialize download buffers with at least the specified size. It's recommended to use the estimated 95 percentile of your image sizes as the initial download buffers size.
IMGPROXY_FREE_MEMORY_INTERVAL
Working with a large amount of data can result in allocating some memory that is generally not used. That's why imgproxy enforces Go's garbage collector to free as much memory as possible and return it to the OS. The default interval of this action is 10 seconds, but you can change it by setting IMGPROXY_FREE_MEMORY_INTERVAL. Decreasing the interval can smooth out the memory usage graph but it can also slow down imgproxy a little. Increasing it has the opposite effect.
IMGPROXY_BUFFER_POOL_CALIBRATION_THRESHOLD
Buffer pools in imgproxy do self-calibration time by time. imgproxy collects stats about the sizes of the buffers returned to a pool and calculates the default buffer size and the maximum size of a buffer that can be returned to the pool. This allows dropping buffers that are too big for most of the images and helps save some memory. By default, imgproxy starts calibration after 1024 buffers have been returned to a pool. You can change this number with the IMGPROXY_BUFFER_POOL_CALIBRATION_THRESHOLD variable. Increasing the number will give you rarer but more accurate calibration.
MALLOC_ARENA_MAX
libvips uses GLib for memory management, and it brings with it GLib memory fragmentation issues to heavily multi-threaded programs. And imgproxy is definitely one of these. First thing you can try if you noticed constantly growing RSS usage without Go's sys memory growth is set MALLOC_ARENA_MAX:
MALLOC_ARENA_MAX=2 imgproxy
This will reduce GLib memory appetites by reducing the number of malloc arenas that it can create. By default GLib creates one are per thread, and this would follow to a memory fragmentation.
Using alternative malloc implementations
If setting MALLOC_ARENA_MAX doesn't show you satisfying results, it's time to try alternative malloc implementations.
jemalloc
jemalloc is a general purpose malloc(3) implementation that emphasizes fragmentation avoidance and scalable concurrency support.
Most Linux distributives provide their jemalloc packages. Using jemalloc doesn't require rebuilding imgproxy or it's dependencies and can be enabled by the LD_PRELOAD environment variable. See the example with Debian below. Note that jemalloc library path may vary on your system.
sudo apt-get install libjemalloc2
LD_PRELOAD='/usr/lib/x86_64-linux-gnu/libjemalloc.so.2' imgproxy
Official imgproxy Docker images starting v3.17.0 have jemalloc preinstalled. Its usage can be enabled by setting the IMGPROXY_MALLOC environment variable to jemalloc.
TCMalloc
TCMalloc is Google's customized implementation of C's malloc() and C++'s operator new used for memory allocation within our C and C++ code. TCMalloc is a fast, multi-threaded malloc implementation.
Most Linux distributives provide their TCMalloc packages. Using TCMalloc doesn't require rebuilding imgproxy or it's dependencies and can be enabled by the LD_PRELOAD environment variable. See the example with Debian below. Note that TCMalloc library path may vary on your system.
sudo apt-get install libtcmalloc-minimal4
LD_PRELOAD='/usr/lib/x86_64-linux-gnu/libtcmalloc_minimal.so.4' imgproxy
Official imgproxy Docker images starting v3.17.0 have TCMalloc preinstalled. Its usage can be enabled by setting the IMGPROXY_MALLOC environment variable to tcmalloc.