Yuka

Today I realized that my Linux Contabo VPS has a built-in script in /etc/cron.hourly that drops the cache every hour. I found it when I checked dmesg; there are so many "drop_caches: 1" lines.

I guess the memory is not dedicated, but shared via KVM memory ballooning.

It seems Contabo tries so hard to reclaim physical memory from its customers by dropping page caches every hour. I feel like Contabo is somewhat notorious for aggressive overprovisioning.

I will delete the free script.

#linux #contabo #mm #kvm #vps

@yonle@fedinet.waltuh.cyou It's not the bright side because unused RAM is wasted.

The Linux kernel will utilize a large amount of free RAM to cache disk r/w. It is a massive speed-up, especially for your database and frequent file reads.

Page caches will automatically be dropped when your processes require more memory. That is the ideal condition.

But given this free script, it's not ideal because Contabo forcibly drops the cache every hour. That means my disk I/O is not properly cached in RAM, even if I have a large amount of RAM.

Dropping the cache means forcing the kernel to read frequently accessed files from slower storage (disk) rather than RAM.

Eheheheh, I should lower my expectations from a cheap VPS. RE: https://casual.pending.io/@eht16/statuses/01KKF2M2HX9P3T5Z8ZD14N0KD8

@ammarfaizi2@hiradai.space @ammarfaizi2@social.gnuweeb.org LGTM, thanks for the fix! root@vmi3114076:~# ls -l /sys/bus/virtio/drivers/virtio_balloon/ total 0 --w------- 1 root root 4096 Mar 13 16:58 bind lrwxrwxrwx 1 root root 0 Mar 13 16:57 module -> ../../../../module/virtio_balloon --w------- 1 root root 4096 Mar 13 16:56 uevent --w------- 1 root root 4096 Mar 13 16:58 unbind lrwxrwxrwx 1 root root 0 Mar 13 16:58 virtio0 -> ../../../../devices/pci0000:00/0000:00:03.0/virtio0 root@vmi3114076:~# root@vmi3114076:~# echo virtio0 > /sys/bus/virtio/drivers/virtio_balloon/unbind root@vmi3114076:~# root@vmi3114076:~# ls -l /sys/bus/virtio/drivers/virtio_balloon/ total 0 --w------- 1 root root 4096 Mar 13 16:58 bind lrwxrwxrwx 1 root root 0 Mar 13 16:57 module -> ../../../../module/virtio_balloon --w------- 1 root root 4096 Mar 13 16:56 uevent --w------- 1 root root 4096 Mar 13 16:58 unbind root@vmi3114076:~# echo virtio0 > /sys/bus/virtio/drivers/virtio_balloon/bind root@vmi3114076:~# ls -l /sys/bus/virtio/drivers/virtio_balloon/ total 0 --w------- 1 root root 4096 Mar 13 16:59 bind lrwxrwxrwx 1 root root 0 Mar 13 16:57 module -> ../../../../module/virtio_balloon --w------- 1 root root 4096 Mar 13 16:56 uevent --w------- 1 root root 4096 Mar 13 16:58 unbind lrwxrwxrwx 1 root root 0 Mar 13 16:59 virtio0 -> ../../../../devices/pci0000:00/0000:00:03.0/virtio0 root@vmi3114076:~#

@ammarfaizi2@social.gnuweeb.org I tried to unbind the virtio balloon but hit by this Command: echo virtio0 > /sys/bus/virtio/drivers/virtio_balloon/unbind dmesg: [ 264.557828] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 264.558955] #PF: supervisor read access in kernel mode [ 264.559786] #PF: error_code(0x0000) - not-present page

@ammarfaizi2@social.gnuweeb.org [ 264.557828] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 264.558955] #PF: supervisor read access in kernel mode [ 264.559786] #PF: error_code(0x0000) - not-present page [ 264.561157] PGD 0 P4D 0 [ 264.561755] Oops: Oops: 0000 [#1] SMP [ 264.562402] CPU: 0 UID: 0 PID: 1345 Comm: bash Not tainted 6.19.3 #8 PREEMPT(none) 125ca1792cd5fca311f47992bbca238807cd563f [ 264.564488] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 264.566384] RIP: 0010:__list_del_entry_valid_or_report+0x5/0xf0 [ 264.567431] Code: 89 d3 49 89 f6 e8 3b 6e c3 ff 49 8b 16 48 c7 c7 b3 c6 63 82 48 89 de 4c 89 f1 e8 56 87 91 ff 0f 0b cc cc cc cc 41 57 41 56 53 <48> 8b 1f 48 85 db 74 38 4c 8b 77 08 4d 85 f6 74 40 49 bf 00 01 00 [ 264.570484] RSP: 0018:ffff888147397ce8 EFLAGS: 00010046 [ 264.571511] RAX: 0000000000000246 RBX: ffff888101c8d800 RCX: 0000000000000001 [ 264.572673] RDX: 000000000080007e RSI: ffffea000404d600 RDI: 0000000000000008 [ 264.573930] RBP: ffff888101c8d800 R08: 0000000000000001 R09: 0000000000000a61 [ 264.576526] R10: 000000000000000f R11: 000000000000000a R12: 0000000000000246 [ 264.578620] R13: ffff888101c8db20 R14: 0000000000000000 R15: ffff888101c8db20 [ 264.579679] FS: 00007fc982d0f740(0000) GS:ffff8883a5c3d000(0000) knlGS:0000000000000000 [ 264.580905] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 264.582218] CR2: 0000000000000008 CR3: 0000000306c67000 CR4: 00000000003506f0 [ 264.583854] Call Trace: [ 264.585550] [ 264.585994] vp_del_vqs+0x121/0x230 [ 264.587128] remove_common+0x135/0x150 [ 264.588097] virtballoon_remove+0xee/0x100 [ 264.589029] virtio_dev_remove+0x3b/0x80 [ 264.589895] device_release_driver_internal+0x187/0x2c0 [ 264.591266] unbind_store+0xb9/0xe0 [ 264.592142] kernfs_fop_write_iter.llvm.11660790530567441834+0xf6/0x180 [ 264.594328] vfs_write+0x2a9/0x3b0 [ 264.595265] ksys_write+0x5c/0xd0 [ 264.597236] do_syscall_64+0x54/0x230 [ 264.598679] entry_SYSCALL_64_after_hwframe+0x29/0x31 [ 264.599672] RIP: 0033:0x7fc982b14907 [ 264.600518] Code: 10 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 48 89 54 24 18 48 89 74 24 [ 264.606759] RSP: 002b:00007fff4dd79878 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 264.608546] RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00007fc982b14907 [ 264.609910] RDX: 0000000000000008 RSI: 000056309e029220 RDI: 0000000000000001 [ 264.611500] RBP: 000056309e029220 R08: 00007fc982bd1460 R09: 000000007fffffff [ 264.612937] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000008 [ 264.614527] R13: 00007fc982c1b780 R14: 00007fc982c17600 R15: 00007fc982c16a00 [ 264.615558]

mov is turing complete 😭 RE: https://infosec.exchange/@ashguy/116122847368289207

@ammarfaizi2@hiradai.space @ammarfaizi2@social.gnuweeb.org

The info pointer is dereferenced. That means the info pointer is expected not to be NULL.

If that is prone to become NULL, would it make sense to have a WARN_ON() in vp_del_vqs()?

In the past, a similar thing also happened on that path https://github.com/torvalds/linux/commit/97ee04feb682c906a1fa973ebe586fe91567d165

Lmao. RE: https://poa.st/objects/65a9bc12-754b-4755-8040-4347c5a0a8de

🍻 RE: https://poa.st/objects/a235c1fb-5477-4f20-ac62-11d648728ec6

I want to buy a bigger VPS, but no money.

😆 RE: https://infosec.exchange/@InsiderTreat/116150417408487190

Sleeping would fix me.

RE: https://mas.to/@returntosender/116191189725041163

Even though I used to really like spicy food, now my stomach can't even take a little bit of it.

@yonle@fedinet.waltuh.cyou Not quick. I don't understand the table structures in your tutorial. I have several questions, but it'll be a bit long to write them now. Not mood.

@yonle@fedinet.waltuh.cyou

good luck

Thanks!

what kind of service you will run here?

What I have planned: Blog, Mail server, web scraper, and Discord bot.

There are more in my backlog. But before that, I'll think about getting a bigger VPS. That means I should first think about how to earn more income.

@yonle@fedinet.waltuh.cyou what happened?

@yonle@fedinet.waltuh.cyou @meowski@fluf.club I see, sorry for the annoyance. I am still new to English. I often misunderstand implicit meaning behind English sentences.

@jimedrand@fedinet.waltuh.cyou it's better to pull rust via rustup rather than apt, because you can change between versions easily with rustup so maybe you want to apt remove rust, then get rustup installed

@ammarfaizi2@hiradai.space @ammarfaizi2@social.gnuweeb.org That works.

I am aware that I am not in good condition right now, and I am doing my best to survive. I am thinking very positively about my future.

@yonle@fedinet.waltuh.cyou I'm not sure if it has a mechanism to limit the cache size. Don't have a strong motivation to look for the answer.

@ammarfaizi2@social.gnuweeb.org @ammarfaizi2@hiradai.space Tested-by: Yuka