From 4b359de75fe85f481d889d0c0ace4086cb130088 Mon Sep 17 00:00:00 2001
From: "Erik M. Bray" <erik.bray@lri.fr>
Date: Thu, 28 Feb 2019 12:15:26 +0100
Subject: [PATCH] Trac #27214: Patch GAP to allocate its memory pool using
 MAP_NORESERVE on Cygwin

---
 ...cPool-0-for-Cygwin-but-do-use-MAP_NO.patch | 78 +++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 build/pkgs/gap/patches/0004-Don-t-set-SyAllocPool-0-for-Cygwin-but-do-use-MAP_NO.patch

diff --git a/build/pkgs/gap/patches/0004-Don-t-set-SyAllocPool-0-for-Cygwin-but-do-use-MAP_NO.patch b/build/pkgs/gap/patches/0004-Don-t-set-SyAllocPool-0-for-Cygwin-but-do-use-MAP_NO.patch
new file mode 100644
index 00000000000..262f16f68ad
--- /dev/null
+++ b/build/pkgs/gap/patches/0004-Don-t-set-SyAllocPool-0-for-Cygwin-but-do-use-MAP_NO.patch
@@ -0,0 +1,78 @@
+From 78506f0a4fba05a238ec6e752c6d3cf2c8336bc8 Mon Sep 17 00:00:00 2001
+From: "Erik M. Bray" <erik.bray@lri.fr>
+Date: Tue, 26 Feb 2019 13:26:11 +0100
+Subject: [PATCH] Don't set SyAllocPool = 0 for Cygwin, but do use
+ MAP_NORESERVE for mmaps on Cygwin
+
+Using MAP_NORESERVE on Cygwin prevents the need to commit physical pages
+for the entirety of mmap'd regions until they are actually used.
+---
+ src/sysmem.c | 16 +++++++++++-----
+ src/system.c |  4 ----
+ 2 files changed, 11 insertions(+), 9 deletions(-)
+
+diff --git a/src/sysmem.c b/src/sysmem.c
+index 68a397b2f..995765828 100644
+--- a/src/sysmem.c
++++ b/src/sysmem.c
+@@ -282,6 +282,12 @@ int SyTryToIncreasePool(void)
+ #define MAP_ANONYMOUS MAP_ANON
+ #endif
+ 
++#ifdef SYS_IS_CYGWIN32
++#define GAP_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE
++#else
++#define GAP_MMAP_FLAGS MAP_PRIVATE|MAP_ANONYMOUS
++#endif
++
+ static void *SyMMapStart = NULL;   /* Start of mmap'ed region for POOL */
+ static void *SyMMapEnd;            /* End of mmap'ed region for POOL */
+ static void *SyMMapAdvised;        /* We have already advised about non-usage
+@@ -342,15 +348,15 @@ void *SyAnonMMap(size_t size) {
+     size = SyRoundUpToPagesize(size);
+ #ifdef SYS_IS_64_BIT
+     /* The following is at 16 Terabyte: */
+-    result = mmap((void *) (16L*1024*1024*1024*1024), size, 
+-                  PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
++    result = mmap((void *) (16L*1024*1024*1024*1024), size,
++                  PROT_READ|PROT_WRITE, GAP_MMAP_FLAGS, -1, 0);
+     if (result == MAP_FAILED) {
+         result = mmap(NULL, size, PROT_READ|PROT_WRITE,
+-            MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
++            GAP_MMAP_FLAGS, -1, 0);
+     }
+ #else
+     result = mmap(NULL, size, PROT_READ|PROT_WRITE,
+-        MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
++        GAP_MMAP_FLAGS, -1, 0);
+ #endif
+     if (result == MAP_FAILED)
+         result = NULL;
+@@ -371,7 +377,7 @@ int SyTryToIncreasePool(void)
+     size = (Int) SyMMapEnd - (Int) SyMMapStart;
+     newchunk = SyRoundUpToPagesize(size/2);
+     result = mmap(SyMMapEnd, newchunk, PROT_READ|PROT_WRITE,
+-                  MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
++                  GAP_MMAP_FLAGS, -1, 0);
+     if (result == MAP_FAILED) return -1;
+     if (result != SyMMapEnd) {
+         munmap(result,newchunk);
+diff --git a/src/system.c b/src/system.c
+index 7423d76bc..6f4c03517 100644
+--- a/src/system.c
++++ b/src/system.c
+@@ -1133,11 +1133,7 @@ void InitSystem (
+ #else
+     SyStorMin = 64 * 1024L;
+     SyStorMax = 1024*1024L;          /* This is in kB! */
+-#ifdef SYS_IS_CYGWIN32
+-    SyAllocPool = 0;                 /* works better on cygwin */
+-#else
+     SyAllocPool = 1536L*1024*1024;   /* Note this is in bytes! */
+-#endif
+ #endif
+     SyStorOverrun = 0;
+     SyStorKill = 0;
+-- 
+2.15.1
+