diff options
Diffstat (limited to 'users/Profpatsch/blog/notes')
| -rw-r--r-- | users/Profpatsch/blog/notes/preventing-oom.md | 33 | ||||
| -rw-r--r-- | users/Profpatsch/blog/notes/rust-string-conversions.md | 53 |
2 files changed, 86 insertions, 0 deletions
diff --git a/users/Profpatsch/blog/notes/preventing-oom.md b/users/Profpatsch/blog/notes/preventing-oom.md new file mode 100644 index 000000000000..59ea4f747700 --- /dev/null +++ b/users/Profpatsch/blog/notes/preventing-oom.md @@ -0,0 +1,33 @@ +tags: linux +date: 2020-01-25 +certainty: likely +status: initial +title: Preventing out-of-memory (OOM) errors on Linux + +# Preventing out-of-memory (OOM) errors on Linux + +I’ve been running out of memory more and more often lately. I don’t use any swap space because I am of the opinion that 16GB of memory should be sufficient for most daily and professional tasks. Which is generally true, however sometimes I have a runaway filling my memory. Emacs is very good at doing this for example, prone to filling your RAM when you open json files with very long lines. + +In theory, the kernel OOM killer should come in and save the day, but the Linux OOM killer is notorious for being extremely … conservative. It will try to free every internal structure it can before even thinking about touching any userspace processes. At that point, the desktop usually stopped responding minutes ago. + +Luckily the kernel provides memory statistics for the whole system, as well as single process, and the [`earlyoom`](https://github.com/rfjakob/earlyoom) tool uses those to keep memory usage under a certain limit. It will start killing processes, “heaviest” first, until the given upper memory limit is satisfied again. + +On NixOS, I set: + +```nix +{ + services.earlyoom = { + enable = true; + freeMemThreshold = 5; # <%5 free + }; +} +``` + +and after activation, this simple test shows whether the daemon is working: + +```shell +$ tail /dev/zero +fish: “tail /dev/zero” terminated by signal SIGTERM (Polite quit request) +``` + +`tail /dev/zero` searches for the last line of the file `/dev/zero`, and since it cannot know that there is no next line and no end to the stream of `\0` this file produces, it will fill the RAM as quickly as physically possible. Before it can fill it completely, `earlyoom` recognizes that the limit was breached, singles out the `tail` command as the process using the most amount of memory, and sends it a `SIGTERM`. diff --git a/users/Profpatsch/blog/notes/rust-string-conversions.md b/users/Profpatsch/blog/notes/rust-string-conversions.md new file mode 100644 index 000000000000..99071ef9d370 --- /dev/null +++ b/users/Profpatsch/blog/notes/rust-string-conversions.md @@ -0,0 +1,53 @@ +# Converting between different String types in Rust + +``` +let s: String = ... +let st: &str = ... +let u: &[u8] = ... +let b: [u8; 3] = b"foo" +let v: Vec<u8> = ... +let os: OsString = ... +let ost: OsStr = ... + +From To Use Comment +---- -- --- ------- +&str -> String String::from(st) +&str -> &[u8] st.as_bytes() +&str -> Vec<u8> st.as_bytes().to_owned() via &[u8] +&str -> &OsStr OsStr::new(st) + +String -> &str &s alt. s.as_str() +String -> &[u8] s.as_bytes() +String -> Vec<u8> s.into_bytes() +String -> OsString OsString::from(s) + +&[u8] -> &str str::from_utf8(u).unwrap() +&[u8] -> String String::from_utf8(u).unwrap() +&[u8] -> Vec<u8> u.to_owned() +&[u8] -> &OsStr OsStr::from_bytes(u) use std::os::unix::ffi::OsStrExt; + +[u8; 3] -> &[u8] &b[..] byte literal +[u8; 3] -> &[u8] "foo".as_bytes() alternative via utf8 literal + +Vec<u8> -> &str str::from_utf8(&v).unwrap() via &[u8] +Vec<u8> -> String String::from_utf8(v) +Vec<u8> -> &[u8] &v +Vec<u8> -> OsString OsString::from_vec(v) use std::os::unix::ffi::OsStringExt; + +&OsStr -> &str ost.to_str().unwrap() +&OsStr -> String ost.to_os_string().into_string() via OsString + .unwrap() +&OsStr -> Cow<str> ost.to_string_lossy() Unicode replacement characters +&OsStr -> OsString ost.to_os_string() +&OsStr -> &[u8] ost.as_bytes() use std::os::unix::ffi::OsStringExt; + +OsString -> String os.into_string().unwrap() returns original OsString on failure +OsString -> &str os.to_str().unwrap() +OsString -> &OsStr os.as_os_str() +OsString -> Vec<u8> os.into_vec() use std::os::unix::ffi::OsStringExt; +``` + + +## Source + +Original source is [this document on Pastebin](https://web.archive.org/web/20190710121935/https://pastebin.com/Mhfc6b9i) |