1 files changed, 63 insertions, 0 deletions
diff --git a/community/ghc/0006-fix-madvise.patch b/community/ghc/0006-fix-madvise.patch
new file mode 100644
index 0000000000..0672001722
--- /dev/null
+++ b/community/ghc/0006-fix-madvise.patch
@@ -0,0 +1,63 @@
+From 6576bf83cdf4eac05eb88a24aa934a736c91e3da Mon Sep 17 00:00:00 2001
+From: Ben Gamari <bgamari.foss@gmail.com>
+Date: Thu, 1 Dec 2016 12:55:23 -0500
+Subject: [PATCH] rts: Ensure we always give MADV_DONTNEED a chance in
+ osDecommitMemory
+
+As described in #12865, newer Linux kernels support both MADV_FREE and
+MADV_DONTNEED. Previously a runtime would fail to try MADV_DONTNEED if
+MADV_FREE failed (e.g. since the kernel which the image is running on
+doesn't support the latter). Now we try MADV_DONTNEED if MADV_FREE
+failed to ensure that binaries compiled on a kernel supporting MADV_FREE
+don't fail on decommit.
+
+Test Plan: Validate
+
+Reviewers: austin, erikd, simonmar
+
+Reviewed By: simonmar
+
+Subscribers: thomie
+
+Differential Revision: https://phabricator.haskell.org/D2780
+
+GHC Trac Issues: #12865
+---
+ rts/posix/OSMem.c | 19 ++++++++++++++++---
+ 1 file changed, 16 insertions(+), 3 deletions(-)
+
+diff --git a/rts/posix/OSMem.c b/rts/posix/OSMem.c
+index 5291745..beffeda 100644
+--- 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");
+ }
+-- 
+1.9.1
+