memsup: prefer platform-specifc used memory calculation over sysconf #10030
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Specially this fixes an issue where the `system_memory_high_watermark`
alarm was being set on Linux since `get_basic_mem` was using the less
accurate sysconf strategy. Despite the comments, `__SC_AVPHYS_PAGES` is
defined in glibc.
Here's an example from before the change. `memsup:get_memory_data()`
calls the C `get_basic_mem` function. The second element in the return
tuple is the used memory (~222 MB) that it was reporting. It should
have returned ~140 MB (254 MB - 114 MB) which also would not have set
the `system_memory_high_watermark` alarm.
```
> memsup:get_memory_data().
{254287872, 222711808, {<0.3654.0>, 3819324}}
> memsup:get_system_memory_data().
[{available_memory,114470912},
{buffered_memory,139264},
{cached_memory,89665536},
{free_memory,33357824},
{free_swap,0},
{system_total_memory,254287872},
{total_memory,254287872},
{total_swap,0}]
```
For consistency, the `__SC_AVPHYS_PAGES` check is done after the
platform-specific checks in both places.
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This fixes an issue where the
system_memory_high_watermarkalarm was being set on Linux sinceget_basic_memwas using the less accurate sysconf strategy. Despite the comments,__SC_AVPHYS_PAGESis defined in glibc (but not musl libc).Here's an example from before the change.
memsup:get_memory_data()calls the Cget_basic_memfunction. The second element in the return tuple is the used memory (~222 MB) that it was reporting. It should have returned ~140 MB (254 MB - 114 MB) which also would not have set thesystem_memory_high_watermarkalarm.For consistency, the
__SC_AVPHYS_PAGEScheck is done after the platform-specific checks in both places.