Explicit GC.gc call does not reclaim memory on 1.11 and master #54020
Description
Here is a simple setup that makes julia memory leak until it is killed by the OS (x86 linux, glibc), on a single thread:
function bar(n)
x = [collect(1:n) for _ in 1:(900_000_000÷n)]
first(last(x))
endI have 8 GiB of RAM available after executing the above. Calling bar(n) once uses around 6.7GiB for any value of n between 1000 and 100_000. That's fine, and this memory used to create and fill x should be reclaimable by GC. But calling bar(n) a second time then crashes julia, even if the two calls are separated by GC.gc(false); GC.gc(true). This occurs on v1.11.0-alpha2 and master (d183ee1), but not on 1.10.2.
liozou@liozou:~$ julia-master/usr/bin/julia -t1 --startup-file=no -E 'bar(n) = (x = [collect(1:n) for _ in 1:(900_000_000÷n)]; first(last(x))); bar(9000);' # master: one call is fine
1
liozou@liozou:~$ julia-master/usr/bin/julia -t1 --startup-file=no -E 'bar(n) = (x = [collect(1:n) for _ in 1:(900_000_000÷n)]; first(last(x))); bar(9000); GC.gc(false); GC.gc(true); bar(9000)' # master: two calls crash
Killed
liozou@liozou:~$ julia-1.11.0-alpha2/bin/julia -t1 --startup-file=no -E 'bar(n) = (x = [collect(1:n) for _ in 1:(900_000_000÷n)]; first(last(x))); bar(9000);' # v1.11: one call is fine
1
liozou@liozou:~$ julia-1.11.0-alpha2/bin/julia -t1 --startup-file=no -E 'bar(n) = (x = [collect(1:n) for _ in 1:(900_000_000÷n)]; first(last(x))); bar(9000); GC.gc(false); GC.gc(true); bar(9000)' # v1.11: two calls crash
Killed
liozou@liozou:~$ julia-1.10.2/bin/julia -t1 --startup-file=no -E 'bar(n) = (x = [collect(1:n) for _ in 1:(900_000_000÷n)]; first(last(x))); bar(9000); bar(9000)' # v1.10 is fine even with two calls
1
(for the sake of completeness, this also used to work on v1.6.6 and v1.7.3, it crashed on v1.8.5 unless an explicit GC.gc() was called between the two bar(9000), and it crashed on v1.9.4 which might be related to #50345)
Irrespective of it being a regression without calling GC.gc, the fact that an explicit GC.gc call does not reclaim the free memory looks like a bug to me. See also #51818, but here function bar exited before the call to GC.gc.
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