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unix: constrained_memory should return UINT64_MAX (#3753)

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Document that we return UINT64_MAX if the cgroup limit is set to the
max. For cgroupv2, that happens if we encounter `max`, while cgroupv1
returns 9223372036854771712 when no limit is set (which according to
[this StackExchange discussion] is derived from LONG_MAX and
PAGE_SIZE). So make sure we also detect this case for cgroupv1.

[this StackExchange discussion]: https://unix.stackexchange.com/questions/420906/what-is-the-value-for-the-cgroups-limit-in-bytes-if-the-memory-is-not-restricte

Addresses: https://github.com/libuv/libuv/pull/3744/files#r974062912
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Tim Besard 2023-05-12 20:34:20 +02:00 committed by GitHub
parent 748d894e82
commit 6ad347fae4
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2 changed files with 16 additions and 4 deletions
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5
docs/src/misc.rst
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@ -586,8 +586,9 @@ API
Gets the total amount of memory available to the process (in bytes) based on
limits imposed by the OS. If there is no such constraint, or the constraint
is unknown, `0` is returned. Note that it is not unusual for this value to
be less than or greater than :c:func:`uv_get_total_memory`.
is unknown, `0` is returned. If there is a constraining mechanism, but there
is no constraint set, `UINT64_MAX` is returned. Note that it is not unusual
for this value to be less than or greater than :c:func:`uv_get_total_memory`.
.. note::
This function currently only returns a non-zero value on Linux, based

15
src/unix/linux.c
View File

@ -1841,7 +1841,7 @@ static uint64_t uv__read_uint64(const char* filename) {
if (0 == uv__slurp(filename, buf, sizeof(buf)))
if (1 != sscanf(buf, "%" PRIu64, &rc))
if (0 == strcmp(buf, "max\n"))
rc = ~0ull;
rc = UINT64_MAX;
return rc;
}
@ -1877,6 +1877,7 @@ static void uv__get_cgroup1_memory_limits(char buf[static 1024], uint64_t* high,
char filename[4097];
char* p;
int n;
uint64_t cgroup1_max;
/* Find out where the controller is mounted. */
p = uv__cgroup1_find_memory_controller(buf, &n);
@ -1893,12 +1894,22 @@ static void uv__get_cgroup1_memory_limits(char buf[static 1024], uint64_t* high,
* as indicated by uv__read_uint64 returning 0.
*/
if (*high != 0 && *max != 0)
return;
goto update_limits;
}
/* Fall back to the limits of the global memory controller. */
*high = uv__read_uint64("/sys/fs/cgroup/memory/memory.soft_limit_in_bytes");
*max = uv__read_uint64("/sys/fs/cgroup/memory/memory.limit_in_bytes");
/* uv__read_uint64 detects cgroup2's "max", so we need to separately detect
* cgroup1's maximum value (which is derived from LONG_MAX and PAGE_SIZE).
*/
update_limits:
cgroup1_max = LONG_MAX & ~(sysconf(_SC_PAGESIZE) - 1);
if (*high == cgroup1_max)
*high = UINT64_MAX;
if (*max == cgroup1_max)
*max = UINT64_MAX;
}
static void uv__get_cgroup2_memory_limits(char buf[static 1024], uint64_t* high,