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authorH.J. Lu <hjl.tools@gmail.com>2016-04-23 06:05:01 -0700
committerH.J. Lu <hjl.tools@gmail.com>2016-04-23 06:05:15 -0700
commit2bc983b78c215765979a29a2e98b0cc01791c2d1 (patch)
treedd39b724f90f6a70a28ee4fd06d1edf8aae743f2
parent00277a3f81bf023d4562da485f62efe5b5b30388 (diff)
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Reduce number of mmap calls from __libc_memalign in ld.so
__libc_memalign in ld.so allocates one page at a time and tries to optimize consecutive __libc_memalign calls by hoping that the next mmap is after the current memory allocation. However, the kernel hands out mmap addresses in top-down order, so this optimization in practice never happens, with the result that we have more mmap calls and waste a bunch of space for each __libc_memalign. This change makes __libc_memalign to mmap one page extra. Worst case, the kernel never puts a backing page behind it, but best case it allows __libc_memalign to operate much much better. For elf/tst-align --direct, it reduces number of mmap calls from 12 to 9. * elf/dl-minimal.c (__libc_memalign): Mmap one extra page.
-rw-r--r--ChangeLog4
-rw-r--r--elf/dl-minimal.c12
2 files changed, 9 insertions, 7 deletions
diff --git a/ChangeLog b/ChangeLog
index 5cd8c4012b..744c0c0fb7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2016-04-23 H.J. Lu <hongjiu.lu@intel.com>
+
+ * elf/dl-minimal.c (__libc_memalign): Mmap one extra page.
+
2016-04-23 Mike Frysinger <vapier@gentoo.org>
* locale/programs/ld-time.c (time_finish): Set week_1stweek to 7
diff --git a/elf/dl-minimal.c b/elf/dl-minimal.c
index 762e65b4d0..c8a8f8dc93 100644
--- a/elf/dl-minimal.c
+++ b/elf/dl-minimal.c
@@ -66,15 +66,13 @@ __libc_memalign (size_t align, size_t n)
if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
{
- /* Insufficient space left; allocate another page. */
+ /* Insufficient space left; allocate another page plus one extra
+ page to reduce number of mmap calls. */
caddr_t page;
size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
- if (__glibc_unlikely (nup == 0))
- {
- if (n)
- return NULL;
- nup = GLRO(dl_pagesize);
- }
+ if (__glibc_unlikely (nup == 0 && n != 0))
+ return NULL;
+ nup += GLRO(dl_pagesize);
page = __mmap (0, nup, PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, -1, 0);
if (page == MAP_FAILED)