From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Ram Pai <linuxram@us.ibm.com>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com,
dave.hansen@intel.com, hbabu@us.ibm.com
Subject: Re: [RFC v2 01/12] powerpc: Free up four 64K PTE bits in 4K backed hpte pages.
Date: Thu, 22 Jun 2017 14:37:27 +0530 [thread overview]
Message-ID: <7348e178-b79e-421a-8dd5-4cfbcd56027a@linux.vnet.ibm.com> (raw)
In-Reply-To: <1497671564-20030-2-git-send-email-linuxram@us.ibm.com>
On 06/17/2017 09:22 AM, Ram Pai wrote:
> Rearrange 64K PTE bits to free up bits 3, 4, 5 and 6
> in the 4K backed hpte pages. These bits continue to be used
> for 64K backed hpte pages in this patch, but will be freed
> up in the next patch.
>
> The patch does the following change to the 64K PTE format
>
> H_PAGE_BUSY moves from bit 3 to bit 9
> H_PAGE_F_SECOND which occupied bit 4 moves to the second part
> of the pte.
> H_PAGE_F_GIX which occupied bit 5, 6 and 7 also moves to the
> second part of the pte.
>
> the four bits((H_PAGE_F_SECOND|H_PAGE_F_GIX) that represent a slot
> is initialized to 0xF indicating an invalid slot. If a hpte
> gets cached in a 0xF slot(i.e 7th slot of secondary), it is
> released immediately. In other words, even though 0xF is a
> valid slot we discard and consider it as an invalid
> slot;i.e hpte_soft_invalid(). This gives us an opportunity to not
> depend on a bit in the primary PTE in order to determine the
> validity of a slot.
>
> When we release a hpte in the 0xF slot we also release a
> legitimate primary slot and unmap that entry. This is to
> ensure that we do get a legimate non-0xF slot the next time we
> retry for a slot.
>
> Though treating 0xF slot as invalid reduces the number of available
> slots and may have an effect on the performance, the probabilty
> of hitting a 0xF is extermely low.
>
> Compared to the current scheme, the above described scheme reduces
> the number of false hash table updates significantly and has the
> added advantage of releasing four valuable PTE bits for other
> purpose.
>
> This idea was jointly developed by Paul Mackerras, Aneesh, Michael
> Ellermen and myself.
>
> 4K PTE format remain unchanged currently.
Scanned through the PTE format again for hash 64K and 4K. It seems
to me that there might be 5 free bits already present on the PTE
format. I might have seriously mistaken something here :) Please
correct me if that is not the case. _RPAGE_RPN* I think is applicable
only for hash page table format and will not be available for radix
later.
+#define _PAGE_FREE_1 0x0000000000000040UL /* Not used */
+#define _RPAGE_SW0 0x2000000000000000UL /* Not used */
+#define _RPAGE_SW1 0x0000000000000800UL /* Not used */
+#define _RPAGE_RPN42 0x0040000000000000UL /* Not used */
+#define _RPAGE_RPN41 0x0020000000000000UL /* Not used */
next prev parent reply other threads:[~2017-06-22 9:07 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-17 3:52 [RFC v2 00/12] powerpc: Memory Protection Keys Ram Pai
2017-06-17 3:52 ` [RFC v2 01/12] powerpc: Free up four 64K PTE bits in 4K backed hpte pages Ram Pai
2017-06-20 10:20 ` Anshuman Khandual
2017-06-20 23:23 ` Ram Pai
2017-06-21 5:35 ` Anshuman Khandual
2017-06-21 6:34 ` Ram Pai
2017-06-21 6:41 ` Aneesh Kumar K.V
2017-06-21 9:30 ` Ram Pai
2017-06-22 9:07 ` Anshuman Khandual [this message]
2017-06-22 16:20 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 02/12] powerpc: Free up four 64K PTE bits in 64K " Ram Pai
2017-06-20 10:51 ` Anshuman Khandual
2017-06-20 23:25 ` Ram Pai
2017-06-21 6:50 ` Aneesh Kumar K.V
2017-06-21 6:54 ` Aneesh Kumar K.V
2017-06-21 20:14 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 03/12] powerpc: Implement sys_pkey_alloc and sys_pkey_free system call Ram Pai
2017-06-19 12:18 ` Michael Ellerman
2017-06-20 22:45 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 04/12] powerpc: store and restore the pkey state across context switches Ram Pai
2017-06-17 3:52 ` [RFC v2 05/12] powerpc: Implementation for sys_mprotect_pkey() system call Ram Pai
2017-06-21 7:16 ` Aneesh Kumar K.V
2017-06-17 3:52 ` [RFC v2 06/12] powerpc: Program HPTE key protection bits Ram Pai
2017-06-20 8:21 ` Anshuman Khandual
2017-06-20 23:26 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 07/12] powerpc: Macro the mask used for checking DSI exception Ram Pai
2017-06-20 8:14 ` Anshuman Khandual
2017-06-20 23:28 ` Ram Pai
2017-06-21 7:25 ` Aneesh Kumar K.V
2017-06-21 9:17 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 08/12] powerpc: Handle exceptions caused by violation of pkey protection Ram Pai
2017-06-20 7:24 ` Anshuman Khandual
2017-06-20 23:43 ` Ram Pai
2017-06-21 3:54 ` Anshuman Khandual
2017-06-21 6:26 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 09/12] powerpc: Deliver SEGV signal on pkey violation Ram Pai
2017-06-20 6:54 ` Anshuman Khandual
2017-06-20 23:56 ` Ram Pai
2017-06-21 3:18 ` Anshuman Khandual
2017-06-21 6:10 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 10/12] powerpc: Read AMR only if pkey-violation caused the exception Ram Pai
2017-06-19 11:06 ` Michael Ellerman
2017-06-19 17:59 ` Ram Pai
2017-06-20 6:46 ` Anshuman Khandual
2017-06-20 23:58 ` Ram Pai
2017-06-20 23:56 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 11/12]Documentation: Documentation updates Ram Pai
2017-06-20 6:18 ` Anshuman Khandual
2017-06-21 0:04 ` Ram Pai
2017-06-17 3:52 ` [RFC v2 12/12]selftest: Updated protection key selftest Ram Pai
2017-06-19 11:04 ` Michael Ellerman
2017-06-20 6:26 ` Anshuman Khandual
2017-06-21 0:10 ` Ram Pai
2017-06-20 5:10 ` [RFC v2 00/12] powerpc: Memory Protection Keys Balbir Singh
2017-06-20 6:05 ` Anshuman Khandual
2017-06-20 9:56 ` Benjamin Herrenschmidt
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