From patchwork Tue Sep 22 02:52:35 2009 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anton Blanchard X-Patchwork-Id: 34031 X-Patchwork-Delegate: benh@kernel.crashing.org Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from bilbo.ozlabs.org (localhost [127.0.0.1]) by ozlabs.org (Postfix) with ESMTP id F18A1B7DD4 for ; Tue, 22 Sep 2009 12:54:04 +1000 (EST) Received: by ozlabs.org (Postfix, from userid 1010) id E771DB7B72; Tue, 22 Sep 2009 12:53:58 +1000 (EST) Date: Tue, 22 Sep 2009 12:52:35 +1000 From: Anton Blanchard To: benh@kernel.crashing.org, MELGOR@ie.ibm.com Subject: powerpc: Move 64bit heap above 1TB on machines with 1TB segments Message-ID: <20090922025235.GD31801@kryten> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Cc: linuxppc-dev@lists.ozlabs.org X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org 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 --- I've cc-ed Mel on this one. As you can see it definitely helps the base page size performance, but I'm a bit worried of the impact of taking away another of our 1TB slices. Index: linux.trees.git/arch/powerpc/kernel/process.c =================================================================== --- linux.trees.git.orig/arch/powerpc/kernel/process.c 2009-09-17 15:47:46.000000000 +1000 +++ linux.trees.git/arch/powerpc/kernel/process.c 2009-09-17 15:49:11.000000000 +1000 @@ -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;