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ghc/ghc-Debian-osdecommitmemory...

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Description: rts: Ensure we always give MADV_DONTNEED a chance in osDecommitMemory
Author: Ben Gamari <bgamari.foss@gmail.com>
Origin: upstream, https://phabricator.haskell.org/D2780
Bug: https://ghc.haskell.org/trac/ghc/ticket/12865
Bug-Debian: https://bugs.debian.org/847677
---
This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
Index: ghc-8.0.2/rts/posix/OSMem.c
===================================================================
--- ghc-8.0.2.orig/rts/posix/OSMem.c
+++ ghc-8.0.2/rts/posix/OSMem.c
@@ -522,11 +522,24 @@
#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");
}