From 5c1f6ee9a31cbdac90bbb8ae1ba4475031ac74b4 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Sun, 28 Apr 2013 09:37:33 +0000 Subject: 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 Acked-by: Paul Mackerras Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/include/asm/mmu-book3e.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/powerpc/include/asm/mmu-book3e.h') diff --git a/arch/powerpc/include/asm/mmu-book3e.h b/arch/powerpc/include/asm/mmu-book3e.h index 99d43e0c1e4a..8bd560c5fe84 100644 --- a/arch/powerpc/include/asm/mmu-book3e.h +++ b/arch/powerpc/include/asm/mmu-book3e.h @@ -231,6 +231,10 @@ typedef struct { u64 high_slices_psize; /* 4 bits per slice for now */ u16 user_psize; /* page size index */ #endif +#ifdef CONFIG_PPC_64K_PAGES + /* for 4K PTE fragment support */ + void *pte_frag; +#endif } mm_context_t; /* Page size definitions, common between 32 and 64-bit -- cgit v1.2.3