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authorAnton Blanchard <anton@samba.org>2009-09-21 16:52:35 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2009-09-24 15:31:44 +1000
commit8bbde7a7062facf8af35bcc9a64cbafe8f36f3cf (patch)
tree4d41cfa5b9a65a39f46933f650e930019346201c /arch/powerpc
parent738ef42e32fe95553a424c04016b936c9f6c9afb (diff)
downloadlwn-8bbde7a7062facf8af35bcc9a64cbafe8f36f3cf.tar.gz
lwn-8bbde7a7062facf8af35bcc9a64cbafe8f36f3cf.zip
powerpc: Move 64bit heap above 1TB on machines with 1TB segments
If we are using 1TB segments and we are allowed to randomise the heap, we can put it above 1TB so it is backed by a 1TB segment. Otherwise the heap will be in the bottom 1TB which always uses 256MB segments and this may result in a performance penalty. This functionality is disabled when heap randomisation is turned off: echo 1 > /proc/sys/kernel/randomize_va_space which may be useful when trying to allocate the maximum amount of 16M or 16G pages. On a microbenchmark that repeatedly touches 32GB of memory with a stride of 256MB + 4kB (designed to stress 256MB segments while still mapping nicely into the L1 cache), we see the improvement: Force malloc to use heap all the time: # export MALLOC_MMAP_MAX_=0 MALLOC_TRIM_THRESHOLD_=-1 Disable heap randomization: # echo 1 > /proc/sys/kernel/randomize_va_space # time ./test 12.51s Enable heap randomization: # echo 2 > /proc/sys/kernel/randomize_va_space # time ./test 1.70s Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/kernel/process.c17
1 files changed, 16 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 0a3216433051..1168c5f440ab 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1165,7 +1165,22 @@ static inline unsigned long brk_rnd(void)
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
- unsigned long ret = PAGE_ALIGN(mm->brk + brk_rnd());
+ unsigned long base = mm->brk;
+ unsigned long ret;
+
+#ifdef CONFIG_PPC64
+ /*
+ * If we are using 1TB segments and we are allowed to randomise
+ * the heap, we can put it above 1TB so it is backed by a 1TB
+ * segment. Otherwise the heap will be in the bottom 1TB
+ * which always uses 256MB segments and this may result in a
+ * performance penalty.
+ */
+ if (!is_32bit_task() && (mmu_highuser_ssize == MMU_SEGSIZE_1T))
+ base = max_t(unsigned long, mm->brk, 1UL << SID_SHIFT_1T);
+#endif
+
+ ret = PAGE_ALIGN(base + brk_rnd());
if (ret < mm->brk)
return mm->brk;