1 00:00:00,000 --> 00:00:10,600 In this video, you learn how to tune kernel parameters. 2 00:00:10,600 --> 00:00:13,000 So how does kernel tuning in general work? 3 00:00:13,000 --> 00:00:18,940 Well, the Linux kernel has many settings that can be tuned through the PROC SYS interface. 4 00:00:18,940 --> 00:00:23,760 For more details about that interface, you can find manproc, because there's a lot of 5 00:00:23,760 --> 00:00:29,440 parameters that can be changed and it's impossible to know about all of them. 6 00:00:29,440 --> 00:00:33,799 Now if you want to change a setting, the new setting can be echoed into the PROC file and 7 00:00:33,799 --> 00:00:36,240 it will be applied immediately. 8 00:00:36,240 --> 00:00:40,560 And that is the recommended methodology if you want to know if you're on the right track 9 00:00:40,560 --> 00:00:43,799 by changing a specific parameter. 10 00:00:43,799 --> 00:00:47,680 For instance, in this class, we are going to tweak the SWAPPINESS parameter. 11 00:00:47,680 --> 00:00:52,040 The SWAPPINESS parameter is a parameter that tells the kernel what to do in case of memory 12 00:00:52,040 --> 00:00:54,279 shortage. 13 00:00:54,279 --> 00:00:57,000 It has a value between 0 and 200. 14 00:00:57,000 --> 00:01:04,080 A value closer to 0 means that it is going to drop inactive cache to make more memory 15 00:01:04,080 --> 00:01:05,080 available. 16 00:01:05,080 --> 00:01:10,500 A value closer to 200 means that the kernel is going to move inactive anonymous memory 17 00:01:10,500 --> 00:01:12,239 to swap. 18 00:01:12,239 --> 00:01:15,559 So echo 30 would be quite conservative. 19 00:01:15,559 --> 00:01:20,120 Now once you have written your parameter and you verified that it works, you are going 20 00:01:20,120 --> 00:01:23,260 to use SYSCTL. 21 00:01:23,260 --> 00:01:24,260 So what is SYSCTL? 22 00:01:24,260 --> 00:01:29,419 Well, SYSCTL is the interface that allows you to manage PROC SYSCTL parameters in an 23 00:01:29,419 --> 00:01:30,419 easy way. 24 00:01:30,419 --> 00:01:35,860 It's a good idea to start with SYSCTL-A, which will show all settings which are available 25 00:01:35,860 --> 00:01:38,820 for tuning on your system. 26 00:01:38,820 --> 00:01:42,540 Notice that the settings that you will see are different according to what is installed 27 00:01:42,540 --> 00:01:47,180 on your system hardware-wise as well as software-wise. 28 00:01:47,180 --> 00:01:53,220 The parameters that you are going to see in the output of SYSCTL-A are filenames. 29 00:01:53,220 --> 00:01:58,160 Filenames relative to slashproc slash sys, where the slash as a separator between directories 30 00:01:58,160 --> 00:02:02,339 and files has been replaced with a dot. 31 00:02:02,339 --> 00:02:11,419 So slashproc slash sys slash vm slash swappiness in SYSCTL-A shows as vm.swappiness. 32 00:02:11,419 --> 00:02:16,619 If you want to make settings persistent, you can write them to etc.sysctl.conf or to a drop-in 33 00:02:16,619 --> 00:02:21,860 file that is created in etc.sysctl.d. 34 00:02:21,860 --> 00:02:26,100 So the value would be, for instance, vm.swappiness is 60. 35 00:02:26,100 --> 00:02:27,100 Write it to a file. 36 00:02:27,100 --> 00:02:31,839 Any name.conf will work, and it will be picked up. 37 00:02:31,839 --> 00:02:37,300 You can activate the changes by rebooting or also by re-reading the configuration file 38 00:02:37,300 --> 00:02:39,660 using sysctl-p. 39 00:02:39,660 --> 00:02:41,399 Let me show you. 40 00:02:41,399 --> 00:02:48,979 So first, let me show you cat to slashproc slash sys slash vm slash swappiness, currently 41 00:02:48,979 --> 00:02:49,979 set to 60. 42 00:02:49,979 --> 00:02:50,979 All right. 43 00:02:51,100 --> 00:02:58,699 So I'm going to echo 150, greater than proc sys vm swappiness. 44 00:02:58,699 --> 00:03:02,979 This is the only way how you can change files in the proc sys file system, because this 45 00:03:02,979 --> 00:03:04,779 is a pseudo file system. 46 00:03:04,779 --> 00:03:08,660 It's not a real file system, so different rules apply. 47 00:03:08,660 --> 00:03:12,699 When I use my cat, I see the new value, and this is where I can do my testing. 48 00:03:12,699 --> 00:03:17,979 For instance, I can use 3 minus m to see if this changes the situation, where we still 49 00:03:17,979 --> 00:03:22,380 see that not a lot of swap is used at all. 50 00:03:22,380 --> 00:03:28,259 That kind of makes sense, because we have still two gigs in available memory. 51 00:03:28,259 --> 00:03:34,740 But maybe if we start Firefox as a background process, maybe that is working, and yeah, 52 00:03:34,740 --> 00:03:38,259 that's not working at all, because I'm trying to start it as root. 53 00:03:38,259 --> 00:03:42,699 Let me try to start it from the graphical user interface. 54 00:03:42,699 --> 00:03:46,740 And then I do my 3 minus m, and what is it showing? 55 00:03:46,779 --> 00:03:49,779 Well, it's showing that still no swap is being used. 56 00:03:49,779 --> 00:03:54,820 It's going off of the available memory, and it doesn't change anything. 57 00:03:54,820 --> 00:03:57,699 That's the thing with these settings in proc sys. 58 00:03:57,699 --> 00:04:01,580 You might think that you're on the wrong track, but there's one way to find out only, and 59 00:04:01,580 --> 00:04:03,339 that is by testing. 60 00:04:03,339 --> 00:04:07,460 Now I'm going to ignore my tests, and I'm going to assume that this is the setting that 61 00:04:07,460 --> 00:04:09,139 I want to have anyway. 62 00:04:09,139 --> 00:04:10,139 Then what would I do? 63 00:04:10,380 --> 00:04:20,100 Well, I would create etc sysctl.d slash swappiness.conf. 64 00:04:20,100 --> 00:04:24,540 It's a good convention to use the name of the parameter followed by .conf, but that's 65 00:04:24,540 --> 00:04:25,899 just a recommendation. 66 00:04:25,899 --> 00:04:28,779 Feel free to do it differently if you want to. 67 00:04:28,779 --> 00:04:37,420 So here I'm putting vm.swappiness is 150. 68 00:04:37,420 --> 00:04:41,260 And next, well, do I need to use sysctl minus b? 69 00:04:41,260 --> 00:04:45,059 Honestly, not really, because I manually set it already. 70 00:04:45,059 --> 00:04:47,540 What is nice is sysctl minus a. 71 00:04:47,540 --> 00:04:52,859 There you can see an overview of all these different tunables, and there is a lot of 72 00:04:52,859 --> 00:04:53,859 them. 73 00:04:53,859 --> 00:04:57,019 On this system, 1,080 in total. 74 00:04:57,019 --> 00:05:02,059 You'll always be around 1,000 parameters, so there's a lot going on there. 75 00:05:02,059 --> 00:05:07,500 Thank you so much that knowing how to optimize your system by using these parameters is really 76 00:05:07,500 --> 00:05:12,899 an art by itself, an art that we are not going to further explore in this video.