From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: paulus@samba.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org
Subject: Re: [RFC PATCH -V2 05/21] powerpc: Reduce PTE table memory wastage
Date: Fri, 22 Feb 2013 10:44:09 +0530 [thread overview]
Message-ID: <871uc9vske.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <20130222003235.GJ21011@truffula.fritz.box>
David Gibson <david@gibson.dropbear.id.au> writes:
> On Thu, Feb 21, 2013 at 10:17:12PM +0530, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>>
>> We now have PTE page consuming only 2K of the 64K page.This is in order to
>> facilitate transparent huge page support, which works much better if our PMDs
>> cover 16MB instead of 256MB.
>>
>> Inorder to reduce the wastage, we now have multiple PTE page fragment
>> from the same PTE page.
>
> This needs a much better description of what you're doing here to
> manage the allocations. It's certainly not easy to figure out from
> the code.
I will add more detailed description in the commit message.
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 be 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. We use the page->_mapcount as bitmap to indicate which
PTE fragments are free.
>
>
> [snip]
>> +#ifdef CONFIG_PPC_64K_PAGES
>> +typedef pte_t *pgtable_t;
>> +#else
>> typedef struct page *pgtable_t;
>> +#endif
>
> This looks really bogus. A pgtable_t is a pointer to PTEs on 64K, but
> a pointer to a struct page on 4k.
>
We enable all the above only with 64K Pages.
-aneesh
next prev parent reply other threads:[~2013-02-22 5:14 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-21 16:47 [RFC PATCH -V2 00/21] THP support for PPC64 Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 01/21] powerpc: Use signed formatting when printing error Aneesh Kumar K.V
2013-02-22 5:00 ` Paul Mackerras
2013-02-21 16:47 ` [RFC PATCH -V2 02/21] powerpc: Save DAR and DSISR in pt_regs on MCE Aneesh Kumar K.V
2013-02-22 5:03 ` Paul Mackerras
2013-02-21 16:47 ` [RFC PATCH -V2 03/21] powerpc: Don't hard code the size of pte page Aneesh Kumar K.V
2013-02-22 5:06 ` Paul Mackerras
2013-02-23 16:17 ` Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 04/21] powerpc: Reduce the PTE_INDEX_SIZE Aneesh Kumar K.V
2013-02-22 5:07 ` Paul Mackerras
2013-02-21 16:47 ` [RFC PATCH -V2 05/21] powerpc: Reduce PTE table memory wastage Aneesh Kumar K.V
2013-02-22 0:32 ` David Gibson
2013-02-22 5:14 ` Aneesh Kumar K.V [this message]
2013-02-22 5:23 ` Paul Mackerras
2013-02-22 17:20 ` Aneesh Kumar K.V
2013-02-23 16:38 ` Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 06/21] powerpc: Add size argument to pgtable_cache_add Aneesh Kumar K.V
2013-02-22 5:27 ` Paul Mackerras
2013-02-21 16:47 ` [RFC PATCH -V2 07/21] powerpc: Use encode avpn where we need only avpn values Aneesh Kumar K.V
2013-02-22 5:28 ` Paul Mackerras
2013-02-21 16:47 ` [RFC PATCH -V2 08/21] powerpc: Decode the pte-lp-encoding bits correctly Aneesh Kumar K.V
2013-02-22 5:37 ` Paul Mackerras
2013-02-24 16:51 ` Aneesh Kumar K.V
2013-02-24 17:45 ` Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 09/21] powerpc: Update tlbie/tlbiel as per ISA doc Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 10/21] powerpc: print both base and actual page size on hash failure Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 11/21] powerpc: Print page size info during boot Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 12/21] powerpc: Fix hpte_decode to use the correct decoding for page sizes Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 13/21] mm/THP: HPAGE_SHIFT is not a #define on some arch Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 14/21] mm/THP: Add pmd args to pgtable deposit and withdraw APIs Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 15/21] mm/THP: support for zerout withdraw Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 16/21] powerpc/THP: Implement transparent huge pages for ppc64 Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 17/21] powerpc/THP: Differentiate THP PMD entries from HUGETLB PMD entries Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 18/21] powerpc/THP: Add code to handle HPTE faults for large pages Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 19/21] powerpc/THP: hypervisor require few WIMG bit set Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 20/21] powerpc/THP: get_user_pages_fast changes Aneesh Kumar K.V
2013-02-21 16:47 ` [RFC PATCH -V2 21/21] powerpc/THP: Enable THP on PPC64 Aneesh Kumar K.V
2013-03-21 8:17 ` [RFC PATCH -V2 00/21] THP support for PPC64 Simon Jeons
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