{"id":83511,"date":"2020-06-01T07:42:29","date_gmt":"2020-06-01T05:42:29","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/proizvoditelnost-raspberry-pi-dobavlyaem-zram-i-izmenyaem-parametry-yadra"},"modified":"2020-06-01T07:42:29","modified_gmt":"2020-06-01T05:42:29","slug":"proizvoditelnost-raspberry-pi-dobavlyaem-zram-i-izmenyaem-parametry-yadra","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/administrirovanie\/proizvoditelnost-raspberry-pi-dobavlyaem-zram-i-izmenyaem-parametry-yadra","title":{"rendered":"Raspberry Pi Performance: Adding ZRAM and Adjusting Kernel Parameters","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

A couple of weeks ago, I published a review of the Pinebook Pro.<\/a><\/noindex>Since the Raspberry Pi 4 is also based on ARM, some of the optimizations mentioned in the previous article are quite suitable for it. I would like to share these tips and find out if you experience similar performance improvements.<\/p>\n

After setting up the Raspberry Pi in my home server<\/a><\/noindex> , I noticed that during moments of memory shortage it became very unresponsive and even froze. To address this problem, I added ZRAM and made several adjustments to the kernel parameters.
\n<\/a><\/noindex><\/p>\n

Activating ZRAM on Raspberry Pi<\/h1>\n

\n\"Raspberry
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\nZRAM<\/a><\/noindex> creates a block storage in RAM named \/dev\/zram0 (or 1, 2, 3, etc.). Pages written to it are compressed and stored in memory. This allows for very fast I\/O operations and also frees up memory through compression.<\/p>\n

The Raspberry Pi 4 comes with 1, 2, 4, or 8 GB of RAM. I will be using the 1 GB model, so adjust the instructions according to your model. With 1 GB, the default swap file (slow!) will be used less frequently. I used the following script zram-swap<\/a><\/noindex> for installation and automatic configuration.<\/p>\n

Instructions are provided in the repository linked above. To install:<\/p>\n

git clone https:\/\/github.com\/foundObjects\/zram-swap.git\ncd zram-swap && sudo .\/install.sh<\/code><\/pre>\n
\nIf you want to edit the config:<\/p>\n
vi \/etc\/default\/zram-swap<\/code><\/pre>\n
\nIn addition, ZRAM can be activated by installing zram-tools<\/code>. If you are using this method, be sure to edit the config<\/b> in the file \/etc\/default\/zramswap<\/code>, and set about 1 GB of ZRAM:<\/p>\n
sudo apt install zram-tools<\/code><\/pre>\n
\nAfter installation, you can check the ZRAM storage statistics with the following command:<\/p>\n
sudo cat \/proc\/swaps\nFilename\t\t\t\tType\t\tSize\tUsed\tPriority\n\/var\/swap                               file\t\t102396\t0\t-2\n\/dev\/zram0                              partition\t1185368\t265472\t5\npi@raspberrypi:~ $<\/code><\/pre>\n
<\/p>\n
Adding kernel parameters for better ZRAM utilization<\/h1>\n
\nNow let's fix the system behavior when the Raspberry Pi resorts to swapping at the last moment, which often leads to freezes. We will add a few lines to the file \/etc\/sysctl.conf<\/b> and reboot.<\/p>\n
These lines will 1) delay the inevitable memory exhaustion<\/b>, increasing pressure on the kernel cache, and 2) start preparing for memory exhaustion earlier<\/b>, initiating swapping in advance. But this will be a much more efficient swap with compressed memory via ZRAM!<\/p>\n
Here are the lines to add to the end of the file \/etc\/sysctl.conf<\/b>:<\/p>\n
vm.vfs_cache_pressure=500\nvm.swappiness=100\nvm.dirty_background_ratio=1\nvm.dirty_ratio=50<\/code><\/pre>\n
\nThen restart the system or activate the changes with the following command:<\/p>\n
sudo sysctl --system<\/code><\/pre>\n
\nvm.vfs_cache_pressure=500<\/b> increases pressure on the cache, which makes the kernel more inclined to reclaim memory used for caching directory objects and indexes. You will use less memory over a longer period. Sudden drops in performance are mitigated by earlier swapping.<\/p>\n
vm.swappiness=100<\/b> increases the parameter that determines how aggressively the kernel will swap memory pages, as we are first using ZRAM.<\/p>\n
vm.dirty_background_ratio=1 & vm.dirty_ratio=50<\/b> \u2014 background processes will start writing immediately upon reaching the 1% limit, but the system will not forcibly perform synchronous I\/O until it reaches the dirty_ratio of 50%.<\/p>\n
These four lines (when used with ZRAM) will help improve performance in case you inevitably<\/u> run out of RAM and start swapping, as I have. Knowing this fact, and considering that memory compression in ZRAM is three times better, it's better to start this swapping earlier.<\/p>\n
Cache pressure helps because we are effectively telling the kernel: 'Hey, listen, I don't have extra memory to use for cache, so please clear it out as soon as possible and keep only the most frequently used\/important data.'<\/p>\n
Even with reduced caching, if over time most of the installed memory is occupied, the kernel will start opportunistic swapping much earlier, so that the CPU (compression) and I\/O for swapping will not drag on until the last moment and utilize all resources at once when it's already too late. ZRAM uses a bit of CPU for compression, but in most low-memory systems, this impacts performance much less than swapping without ZRAM.<\/p>\n
In conclusion<\/h1>\n
\nLet's take a look at the result again:<\/p>\n
pi@raspberrypi:~ $ free -h\ntotal used free shared buff\/cache available\nMem: 926Mi 471Mi 68Mi 168Mi 385Mi 232Mi\nSwap: 1.2Gi 258Mi 999Mi\n\npi@raspberrypi:~ $ sudo cat \/proc\/swaps \nFilename Type Size Used Priority\n\/var\/swap file 102396 0 -2\n\/dev\/zram0 partition 1185368 264448 5<\/code><\/pre>\n
\n264448 in ZRAM is nearly one gigabyte of uncompressed data. Everything went into ZRAM, and nothing ended up in the much slower swap file. Try these settings for yourself; they work on all Raspberry Pi models. My unusable, hanging system has turned into a functional and stable one.<\/p>\n
In the near future, I hope to continue and update this article with some results from testing the system before and after installing ZRAM. Right now, I just don\u2019t have the time for it. Meanwhile, feel free to perform your own tests and let me know in the comments. The Raspberry Pi 4 is simply a beast with these settings. Enjoy!<\/p>\n
On the topic:<\/b><\/p>\n