When HUGETLB_SHARE=1, read-only text segments are copied to a file on
a hugetlbfs mount and shared between multiple processes. However with
kernel 2.6.27 and later, the expectation is that pages will be reserved for
MAP_PRIVATE mappings as well as MAP_SHARED. This will render HUGETLB_SHARE
ineffective as huge pages will be reserved that already exist in the page
cache. This patch disables reservations for read-only mappings when sharing
is enabled on the assumption mprotect() will never be called for remapped
read-only segments.
Signed-off-by: Mel Gorman <[EMAIL PROTECTED]>
---
diff --git a/elflink.c b/elflink.c
index 2816f8f..fdb5698 100644
--- a/elflink.c
+++ b/elflink.c
@@ -1035,6 +1035,7 @@ static void remap_segments(struct seg_info *seg, int num)
unsigned long start, offset, mapsize;
long page_size = getpagesize();
long hpage_size = gethugepagesize();
+ int mmap_flags;
/*
* XXX: The bogus call to mmap below forces ld.so to resolve the
@@ -1064,9 +1065,19 @@ static void remap_segments(struct seg_info *seg, int num)
start = ALIGN_DOWN((unsigned long)seg[i].vaddr, hpage_size);
offset = (unsigned long)(seg[i].vaddr - start);
mapsize = ALIGN(offset + seg[i].memsz, hpage_size);
+ mmap_flags = MAP_PRIVATE|MAP_FIXED;
+
+ /*
+ * If HUGETLB_SHARE is enabled and this is a read-only
+ * segment, then use MAP_NORESERVE. The assumption is that
+ * the pages already exist in the hugetlbfs file and that
+ * mprotect() will not be called requiring a COW
+ */
+ if (sharing && !(seg[i].prot & PROT_WRITE))
+ mmap_flags |= MAP_NORESERVE;
p = mmap((void *) start, mapsize, seg[i].prot,
- MAP_PRIVATE|MAP_FIXED, seg[i].fd, 0);
+ mmap_flags, seg[i].fd, 0);
if (p == MAP_FAILED)
unmapped_abort("Failed to map hugepage segment %u: "
"%p-%p (errno=%u)\n", i, start,
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