From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Alexey Kardashevskiy <aik@au1.ibm.com>,
linuxppc-dev@lists.ozlabs.org, paulus@samba.org
Subject: Re: [PATCH -V10 00/15] THP support for PPC64
Date: Wed, 19 Jun 2013 09:00:05 +0530 [thread overview]
Message-ID: <87zjumhj5u.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1371593004.21896.199.camel@pasglop>
Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:
> On Wed, 2013-06-19 at 00:16 +0530, Aneesh Kumar K.V wrote:
>
>> But will that by anonymous memory ? ie, will we find them suitable for
>> THP allocation ?
>
> The 4k pages themselves with 4k_PFN no, but the segment yes. A single of
> these will demote the whole segment, ie 256M or 1T.
>
>> > * If you find a THP in hash_page and the segment size is 4k, fault
>> >
>> > * In do_page_fault, re-check for that condition (or maybe we can make
>> > hash_page return a specific bit that gets ORed into the error_code into
>> > do_page_fault ?) and split huge pages there.
>> >
>> > But that's just an idea off the top of my mind, there might be a better
>> > way. Of course this needs to be tested.
>> >
>> > BTW. For the subpage protection, similarily, you need to make sure you
>> > properly map the entire segment as "no THP", not just the range
>> > passed-in by the user.
>>
>> Can you explain that more, why should the entire segment be marked no THP ?
>> The segment can work with 4K base page size and we still be able to
>> allocate a hugepage in that segment.
>
> Will we be able to track all the possible hashings of the huge page on a
> 4k segment ?
Yes. The comment above hpte_valid explains that
* The linux hugepage PMD now include the pmd entries followed by the address
* to the stashed pgtable_t. The stashed pgtable_t contains the hpte bits.
* [ 1 bit secondary | 3 bit hidx | 1 bit valid | 000]. We use one byte per
* each HPTE entry. With 16MB hugepage and 64K HPTE we need 256 entries and
* with 4K HPTE we need 4096 entries. Both will fit in a 4K pgtable_t.
-aneesh
next prev parent reply other threads:[~2013-06-19 3:30 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-05 15:28 [PATCH -V10 00/15] THP support for PPC64 Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 01/15] powerpc/mm: handle hugepage size correctly when invalidating hpte entries Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 02/15] powerpc/THP: Double the PMD table size for THP Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 03/15] powerpc/THP: Implement transparent hugepages for ppc64 Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 04/15] powerpc: move find_linux_pte_or_hugepte and gup_hugepte to common code Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 05/15] powerpc: Update find_linux_pte_or_hugepte to handle transparent hugepages Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 06/15] powerpc: Replace find_linux_pte with find_linux_pte_or_hugepte Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 07/15] powerpc: Update gup_pmd_range to handle transparent hugepages Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 08/15] powerpc/THP: Add code to handle HPTE faults for hugepages Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 09/15] powerpc: Make linux pagetable walk safe with THP enabled Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 10/15] powerpc: Prevent gcc to re-read the pagetables Aneesh Kumar K.V
2013-06-05 15:41 ` David Laight
2013-06-05 22:39 ` Benjamin Herrenschmidt
2013-06-05 15:28 ` [PATCH -V10 11/15] powerpc/THP: Enable THP on PPC64 Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 12/15] powerpc: Optimize hugepage invalidate Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 13/15] powerpc: disable assert_pte_locked for collapse_huge_page Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 14/15] powerpc: use smp_rmb when looking at deposisted pgtable to store hash index Aneesh Kumar K.V
2013-06-05 15:28 ` [PATCH -V10 15/15] powerpc: split hugepage when using subpage protection Aneesh Kumar K.V
2013-06-05 23:31 ` [PATCH -V10 00/15] THP support for PPC64 Benjamin Herrenschmidt
2013-06-06 0:13 ` Andrew Morton
2013-06-06 6:05 ` Aneesh Kumar K.V
2013-06-06 7:20 ` Andrew Morton
2013-06-16 2:00 ` Benjamin Herrenschmidt
2013-06-16 3:37 ` Benjamin Herrenschmidt
2013-06-16 4:06 ` Benjamin Herrenschmidt
2013-06-16 23:02 ` Benjamin Herrenschmidt
2013-06-18 18:46 ` Aneesh Kumar K.V
2013-06-18 22:03 ` Benjamin Herrenschmidt
2013-06-19 3:30 ` Aneesh Kumar K.V [this message]
2013-06-18 17:54 ` Aneesh Kumar K.V
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