From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
paulus@samba.org, mpe@ellerman.id.au
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 18/31] powerpc/mm: Increase the pte frag size.
Date: Mon, 21 Sep 2015 14:15:08 +0530 [thread overview]
Message-ID: <87mvwgduuj.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <1442823285.2819.1.camel@kernel.crashing.org>
Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:
> On Mon, 2015-09-21 at 12:10 +0530, Aneesh Kumar K.V wrote:
>> /*
>> - * We use a 2K PTE page fragment and another 2K for storing
>> - * real_pte_t hash index
>> + * We use a 2K PTE page fragment and another 4K for storing
>> + * real_pte_t hash index. Rounding the entire thing to 8K
>> */
>
> Isn't this a LOT of memory wasted ? Page tables have a non-negligible
> footprint, we were already wasting half, now we are wasting 3/4 no ?
>
The actual math is, we used to allocate 16 PTE page from a 64K page
before. We now do 8 pte page from a 64K linux page.
> Ie, in most cases on modern machines we never use the other "half"...
>
That is true. We will use this only when we use 4K subpage. But I am
not sure there is a better solution. Also, we should find this slightly
imporve our contention on ptl lock. With SPLIT_PTLOCK we now have less
number of pte page using the same spin lock.
-aneesh
next prev parent reply other threads:[~2015-09-21 8:45 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-21 6:40 [PATCH 00/31] powerpc/mm: Update page table format for book3s 64 Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 01/31] powerpc/mm: move pte headers to book3s directory Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 02/31] powerpc/mm: move pte headers to book3s directory (part 2) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 03/31] powerpc/mm: make a separate copy for book3s Aneesh Kumar K.V
2015-09-21 21:58 ` Scott Wood
2015-09-22 6:42 ` Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 04/31] powerpc/mm: make a separate copy for book3s (part 2) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 05/31] powerpc/mm: Move hash specific pte width and other defines to book3s Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 06/31] powerpc/mm: Delete booke bits from book3s Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 07/31] powerpc/mm: Don't have generic headers introduce functions touching pte bits Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 08/31] powerpc/mm: Drop pte-common.h from BOOK3S 64 Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 09/31] powerpc/mm: Don't use pte_val as lvalue Aneesh Kumar K.V
2015-09-22 2:22 ` Scott Wood
2015-09-22 6:44 ` Aneesh Kumar K.V
2015-09-22 6:46 ` Scott Wood
2015-09-21 6:40 ` [PATCH 10/31] powerpc/mm: Don't use pmd_val, pud_val and pgd_val " Aneesh Kumar K.V
2015-09-22 2:23 ` Scott Wood
2015-09-22 6:45 ` Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 11/31] powerpc/mm: Move hash64 PTE bits from book3s/64/pgtable.h to hash.h Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 12/31] powerpc/mm: Move PTE bits from generic functions to hash64 functions Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 13/31] powerpc/booke: Move booke headers (part 1) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 14/31] powerpc/booke: Move booke headers (part 2) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 15/31] powerpc/booke: Move booke headers (part 3) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 16/31] powerpc/booke: Move booke headers (part 4) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 17/31] powerpc/booke: Move booke headers (part 5) Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 18/31] powerpc/mm: Increase the pte frag size Aneesh Kumar K.V
2015-09-21 8:14 ` Benjamin Herrenschmidt
2015-09-21 8:45 ` Aneesh Kumar K.V [this message]
2015-09-21 11:06 ` Benjamin Herrenschmidt
2015-09-21 11:53 ` Aneesh Kumar K.V
2015-09-23 21:37 ` Benjamin Herrenschmidt
2015-09-28 4:55 ` Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 19/31] powerpc/mm: Convert 4k hash insert to C Aneesh Kumar K.V
2015-09-21 8:16 ` Benjamin Herrenschmidt
2015-09-21 8:57 ` Aneesh Kumar K.V
2015-09-29 8:13 ` Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 20/31] powerpc/mm: update __real_pte to take address as argument Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 21/31] powerpc/mm: make pte page hash index slot 8 bits Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 22/31] powerpc/mm: Don't track subpage valid bit in pte_t Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 23/31] powerpc/mm: Increase the width of #define Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 24/31] powerpc/mm: Convert __hash_page_64K to C Aneesh Kumar K.V
2015-09-23 13:56 ` Anshuman Khandual
2015-09-28 4:58 ` Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 25/31] powerpc/mm: Convert 4k insert from asm " Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 26/31] powerpc/mm: Remove the dependency on pte bit position in asm code Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 27/31] powerpc/mm: Add helper for converting pte bit to hpte bits Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 28/31] powerpc/mm: Move WIMG update to helper Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 29/31] powerpc/mm: Move hugetlb related headers Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 30/31] powerpc/mm: Move THP headers around Aneesh Kumar K.V
2015-09-21 6:40 ` [PATCH 31/31] powerpc/mm: Add a _PAGE_PTE bit Aneesh Kumar K.V
2015-09-21 21:48 ` [PATCH 00/31] powerpc/mm: Update page table format for book3s 64 Scott Wood
2015-09-22 6:48 ` Aneesh Kumar K.V
2015-09-22 6:57 ` Scott Wood
2015-09-28 4:56 ` Aneesh Kumar K.V
2015-09-28 16:41 ` Scott Wood
2015-09-30 1:44 ` Michael Ellerman
2015-09-29 0:12 ` Benjamin Herrenschmidt
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