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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2013-04-28 09:37:33 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2013-04-30 16:00:07 +1000
commit5c1f6ee9a31cbdac90bbb8ae1ba4475031ac74b4 (patch)
tree9b68dca4f1968199567b2fe631f346795d8eee69 /arch/powerpc/kernel/setup_64.c
parentd614bb041209fd7cb5e4b35e11a7b2f6ee8f62b8 (diff)
downloadop-kernel-dev-5c1f6ee9a31cbdac90bbb8ae1ba4475031ac74b4.zip
op-kernel-dev-5c1f6ee9a31cbdac90bbb8ae1ba4475031ac74b4.tar.gz
powerpc: Reduce PTE table memory wastage
We allocate one page for the last level of linux page table. With THP and large page size of 16MB, that would mean we are wasting large part of that page. To map 16MB area, we only need a PTE space of 2K with 64K page size. This patch reduce the space wastage by sharing the page allocated for the last level of linux page table with multiple pmd entries. We call these smaller chunks PTE page fragments and allocated page, PTE page. In order to support systems which doesn't have 64K HPTE support, we also add another 2K to PTE page fragment. The second half of the PTE fragments is used for storing slot and secondary bit information of an HPTE. With this we now have a 4K PTE fragment. We use a simple approach to share the PTE page. On allocation, we bump the PTE page refcount to 16 and share the PTE page with the next 16 pte alloc request. This should help in the node locality of the PTE page fragment, assuming that the immediate pte alloc request will mostly come from the same NUMA node. We don't try to reuse the freed PTE page fragment. Hence we could be waisting some space. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/kernel/setup_64.c')
-rw-r--r--arch/powerpc/kernel/setup_64.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 75fbaceb..e379d3f 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -583,7 +583,9 @@ void __init setup_arch(char **cmdline_p)
init_mm.end_code = (unsigned long) _etext;
init_mm.end_data = (unsigned long) _edata;
init_mm.brk = klimit;
-
+#ifdef CONFIG_PPC_64K_PAGES
+ init_mm.context.pte_frag = NULL;
+#endif
irqstack_early_init();
exc_lvl_early_init();
emergency_stack_init();
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