memory: Avoid estimating available memory, use kernel estimate instead #2160
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`/proc/meminfo` states that it's report values are in KB, when they actually are in KiB. Previously, this inconsistency leaked into the whole code for this block (which had to add `* 1024` after nearly every assignment). Now this inconsistency is contained to the `Memstate` structure.
`free`, `btop` and other tools (like the `sysinfo` rust library) use `mem_total - mem_avail` to calculate the used memory. As explained in the already linked [kernel commit][1], `mem_avail` is an estimate of the available memory based on the current way the kernel handles memory. The previous logic for calculating used memory tried to estimate this based on `mem_free`, `buffers`, `pagecache` and `reclaimable`. Unfortunately, as the kernel commit message predicts, this user space estimate bitrots, as the kernel memory usage patterns change. Thus, we now simply use the kernel estimate `mem_avail` as we know that that is in-sync with the relevant kernel internals. [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773
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free,btopand other tools (like thesysinforust library) usemem_total - mem_availto calculate the used memory. As explained in the already linked kernel commit,mem_availis an estimate of the available memory based on the current way the kernel handles memory.The previous logic for calculating used memory tried to estimate this based on
mem_free,buffers,pagecacheandreclaimable. Unfortunately, as the kernel commit message predicts, this user space estimate bitrots, as the kernel memory usage patterns change.Thus, we now simply use the kernel estimate
mem_availas we know that that is in-sync with the relevant kernel internals.