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Zheng Luo htfy96

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htfy96 /
Last active Jun 21, 2020
How to delete a bunch of files on server without interrupting other workload in 2020

What doesn't work


Two reasons:

  • Common answer: Many modern OS doesn't use BFQ scheduler, and deadline-related schedulers ignore ionice: check this with cat /sys/block/sda/queue/scheduler
  • In kernel, the IO on writeback pages isn't accounted to the actual process until cgroup v2 OR blkio scheduler. So, if you deleted some files which updates the dentry page cache of parent directory, the writeback page cache won't be accounted to the user and thus stay unlimited

What does work


htfy96 / install_dep_and_build
Created Dec 5, 2019
Install conan packages and build with cmake_multi generator
View install_dep_and_build
# Usage:
# Assuming you are in ROOT/build
# and ROOT contains conanfile.txt and CMakeLists.txt
# ./install_dep_and_build [Debug|Release|RelWithDebInfo]
# Prerequisite:
# Make sure you have
# [generators]
_deps/wasiclang-src/opt/wasi-sdk/bin/clang --sysroot _deps/wasiclang-src/opt/wasi-sdk/share/wasi-sysroot stb_vorbis.c -c -o stb_vorbis.
_deps/wasiclang-src/opt/wasi-sdk/bin/clang -Wl,--export-all --sysroot _deps/wasiclang-src/opt/wasi-sdk/share/wasi-sysroot *.o -o lib.wasm
cargo/release/lucetc --bindings _deps/mod_lucet-src/lucet-wasi/bindings.json --reserved-size 256MiB lib.wasm -o --opt-level 2
htfy96 / childexit-pipe.c
Created Sep 23, 2019
Detecting child exit with pipe
View childexit-pipe.c
#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>
#include <sys/select.h>
#include <stdbool.h>
htfy96 / cdq.cpp
Last active Dec 19, 2018
Solution to CF Educational Round 56 Problem E, with CDQ divide-and-conquer (CDQ分治)
View cdq.cpp
#include <bits/stdc++.h>
Convert all modification and query into single-point events (t, x, y). Initially sort by t,
for each interval, recursively handle independent two parts. Then calc the interference
between part one and two: only mod in part 1 can affect result in part 2. Therefore, we can
sort part1 and 2 respectively by x, then process all mod event in part 1 and all query events in
part 2 in a sort-merge-like way. The Y-dimension is maintained with a fenwick tree.
In the end all elements will be sorted by x.
View discrete.cpp
#include <bits/stdc++.h>
using namespace std;
int main()
vector<int> a {1, 3, 3, 2, 5};
vector<int> b;
for (int i=0; i<a.size(); ++i)
htfy96 /
Created Sep 19, 2018
Proof of identication

I hereby claim:

  • I am the person who sends Wechat messages and moments at Sept 18 22:07 - 22:17 PDT from account @VicLuo96

To claim this, I sign this message with my pubkey 0x98809CA08BF5662A:

I hereby claim:

- I am the person who sends Wechat messages and moments at Sept 18 22:07 - 22:17 PDT from account @VicLuo96
htfy96 / A-small-attempt-3.out
Created Jul 29, 2018
GCJ Kickstart Round D Problem A: Solution and sample data
View A-small-attempt-3.out
Case #1: 13
Case #3: 2
Case #4: 386239
Case #8: 84609596512776
Case #9: 0
Case #10: 1155268877829
htfy96 / feeds.opml
Created Jun 27, 2018
My feedly feeds collection
View feeds.opml
<?xml version="1.0" encoding="UTF-8"?>
<opml version="1.0">
<title>Vic subscriptions in feedly Cloud</title>
<outline text="news" title="news">
<outline type="rss" text="路透: 时事要闻" title="路透: 时事要闻" xmlUrl="" htmlUrl=""/>
<outline type="rss" text="Washington Post: Breaking News, World, US, DC News &amp; Analysis" title="Washington Post: Breaking News, World, US, DC News &amp; Analysis" xmlUrl="" htmlUrl=""/>
htfy96 /
Last active Dec 19, 2018
Restrict C++ unsafe behaviors in unsafe{} block using clang-query and simple commands

C++ has a lot of dark corners. Unfortunately, sometimes we need to allow inexperienced developers to write some C++ code to meet the deadline. The intersection of the two cases often makes things worse: programmers used to delegate memory management to garbage collection tend to throw off new everywhere in the source, and those stuck with compile error will use every evil hack to get around with it. Code review is a feasible way to ensure code quality in this case, but a better choice is to restrict them into a relatively safe subset of the language.

In this article, I will show how to use clang-query and a simple script to restrict some unsafe behaviors in unsafe block/namespace using simple commands:

#include "common.hpp"

struct X {
    int f: 2; // error: use of bit field without enclosing Unsafe
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