f6cccefed5
* gnu/packages/patches/ghc-8.0-fall-back-to-madv_dontneed.patch: New file. * gnu/local.mk (dist_patch_DATA): Add it. * gnu/packages/haskell.scm (ghc-8): Use it.
61 lines
2.3 KiB
Diff
61 lines
2.3 KiB
Diff
ghc runtime by default (otherwise depending on a "configure" option)
|
|
does memory allocation on their own by first mmapping a 1 TB range of
|
|
memory into the process and then parceling out chunks from it.
|
|
|
|
If one of the chunks is not needed, the kernel needs to be informed -
|
|
otherwise the system would quickly run out of available RAM.
|
|
|
|
ghc does that via madvise(2).
|
|
|
|
There are two options when doing this informing:
|
|
|
|
MADV_FREE - Means "I don't need this range or the data in it any more".
|
|
Kernel promises to fail later accesses to it.
|
|
|
|
MADV_DONTNEED - Means "I don't need this range right now - and I don't
|
|
need the data in it anymore". Kernel promises to make later accesses to
|
|
it succeed (if necessary by providing a new page initialized with zeroes).
|
|
|
|
MADV_FREE was introduced in Linux 4.5.
|
|
glibc 2.25 and later always define MADV_FREE.
|
|
|
|
Unpatched ghc 8.0.2 will use either MADV_FREE or MADV_DONTNEED, determined
|
|
at ghc compile time. Which of them will actually succeed is determined
|
|
by the Linux kernel at run time.
|
|
|
|
This patch makes ghc try MADV_FREE. If it doesn't work, it falls back to
|
|
MADV_DONTNEED.
|
|
|
|
The end result is that ghc programs free their memory with Linux < 4.5 again.
|
|
|
|
See https://git.haskell.org/ghc.git/commitdiff/6576bf83cdf4eac05eb88a24aa934a736c91e3da for more information.
|
|
--- a/rts/posix/OSMem.c
|
|
+++ b/rts/posix/OSMem.c
|
|
@@ -541,11 +541,24 @@ void osDecommitMemory(void *at, W_ size)
|
|
|
|
#ifdef MADV_FREE
|
|
// Try MADV_FREE first, FreeBSD has both and MADV_DONTNEED
|
|
- // just swaps memory out
|
|
+ // just swaps memory out. Linux >= 4.5 has both DONTNEED and FREE; either
|
|
+ // will work as they both allow the system to free anonymous pages.
|
|
+ // It is important that we try both methods as the kernel which we were
|
|
+ // built on may differ from the kernel we are now running on.
|
|
r = madvise(at, size, MADV_FREE);
|
|
-#else
|
|
- r = madvise(at, size, MADV_DONTNEED);
|
|
+ if(r < 0) {
|
|
+ if (errno == EINVAL) {
|
|
+ // Perhaps the system doesn't support MADV_FREE; fall-through and
|
|
+ // try MADV_DONTNEED.
|
|
+ } else {
|
|
+ sysErrorBelch("unable to decommit memory");
|
|
+ }
|
|
+ } else {
|
|
+ return;
|
|
+ }
|
|
#endif
|
|
+
|
|
+ r = madvise(at, size, MADV_DONTNEED);
|
|
if(r < 0)
|
|
sysErrorBelch("unable to decommit memory");
|
|
}
|