JUjulian37·Oct 1, 2021
You can do mmap on Windows, eg. https://github.com/danburkert/memmap-rs
In Freqfs: In-memory filesystem cache for Rustdanburkert
memmap-rs
Rust2016–2021
danburkert / memmap-rs
memmap-rs
cross-platform Rust API for memory mapped IO
2Distinct people
2Mentions
0Explicit recommenders
577GitHub stars
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What it is
cross-platform Rust API for memory mapped IO
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This week on Hacker News
Nov 7–Nov 14 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/14/2026, 3:56:07 PM UTC.
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HN mentions by year2 dated mentions
Observed mentions: 2016-09-24 19:30:00 UTC to 2021-10-01 21:35:39 UTC.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 1 | 0 | 1 |
What Hacker News says
2 sourcesI did some experimentation last night as well. I suspected a lot of the cost came from the unmapping the files and the required invalidations and TLB shootdowns required to do so.
I made rg simply not munmap files when it was done with them (I made this drop do nothing: https://github.com/danburkert/memmap-rs/blob/master/src/unix...)
Searching for PM_RESUME in the Linux source gave me these results:
--no-mmap: ~400ms
--mmap (with munmap): ~750ms
--mmap (without munmap): ~550ms
So eliding munmap made a big difference, but it was still not enough to beat out reading the files. perf shows that the mmap syscall itself is just too expensive (this is --mmap (with munmap)):
Children Self Command Shared Object Symbol
- 81.88% 0.00% rg rg [.] __rust_try
- __rust_try
Read the rest
- 50.57% std::panicking::try::call::ha112cda315d6c57d
- 47.73% rg::Worker::search_mmap::h5179a76c63e344d0
- 23.91% __GI___munmap
6.08% smp_call_function_many
3.14% rwsem_spin_on_owner
1.86% native_queued_spin_lock_slowpath
0.94% osq_lock
0.67% native_write_msr_safe
0.52% unmap_page_range
+ 21.41% _$LT$rg..search_buffer..BufferSearcher$LT$$u27$a$C$$u20$W$GT$$GT$::run::hd0f8b2830716be0c
0.80% memchr
- 17.99% __mmap64
5.20% rwsem_down_write_failed
1.96% rwsem_spin_on_owner
0.77% osq_lock
0.59% native_queued_spin_lock_slowpath
+ 6.79% 0x1080d
1.72% __GI___libc_close
1.27% __memcpy_sse2_unaligned
0.98% __fxstat64
0.56% __GI___ioctl