From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Will Deacon <will@kernel.org>,
Muchun Song <muchun.song@linux.dev>,
linux-mm@kvack.org, npiggin@gmail.com,
Catalin Marinas <catalin.marinas@arm.com>,
Dan Williams <dan.j.williams@intel.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
linuxppc-dev@lists.ozlabs.org,
Joao Martins <joao.m.martins@oracle.com>,
Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64
Date: Thu, 27 Jul 2023 11:07:18 +0530 [thread overview]
Message-ID: <87bkfxx6cx.fsf@linux.ibm.com> (raw)
In-Reply-To: <20230726115246.b6ed2a08aa7b648671107a8a@linux-foundation.org>
Andrew Morton <akpm@linux-foundation.org> writes:
> On Wed, 26 Jul 2023 10:59:32 +0530 Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> wrote:
>
>> On 7/26/23 12:59 AM, Andrew Morton wrote:
>> > On Tue, 25 Jul 2023 00:37:46 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:
>> >
>> >> This patch series implements changes required to support DAX vmemmap
>> >> optimization for ppc64.
>> >
>> > Do we have any measurements to help us understand the magnitude
>> > of this optimization?
>> >
>> > And any documentation which helps users understand whether and
>> > why they should enable this feature?
>>
>> That is memory space optimization due to kernel reusing the tail page struct pages. The details
>> of the optimization is documented in patch 11. We document there the impact with both 4k and
>> 64K page size.
>
> I suppose that with sufficient arithmetic one could use
> Documentation/powerpc/vmemmap_dedup.rst to figure out the bottom-line
> savings.
>
> I was more expecting a straightforward statement in the [0/N] overview
> to help people understand why they're reading this patchset at all.
> Like "saves 5% of total memory on my XXX machine".
This is specific to devdax usage and also depends on devdax alignment.
The actual saving details are also documented in mm/vmemmap_dedup.rst.
The saving will be based on the devdax device memory size and aligment.
With 64K page size for 16384 pages added (1G) we save 14 pages
With 4K page size for 262144 pages added (1G) we save 4094 pages
With 4K page size for 512 pages added (2M) we save 6 pages
-aneesh
WARNING: multiple messages have this Message-ID (diff)
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, mpe@ellerman.id.au,
linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com,
christophe.leroy@csgroup.eu, Oscar Salvador <osalvador@suse.de>,
Mike Kravetz <mike.kravetz@oracle.com>,
Dan Williams <dan.j.williams@intel.com>,
Joao Martins <joao.m.martins@oracle.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Muchun Song <muchun.song@linux.dev>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64
Date: Thu, 27 Jul 2023 11:07:18 +0530 [thread overview]
Message-ID: <87bkfxx6cx.fsf@linux.ibm.com> (raw)
In-Reply-To: <20230726115246.b6ed2a08aa7b648671107a8a@linux-foundation.org>
Andrew Morton <akpm@linux-foundation.org> writes:
> On Wed, 26 Jul 2023 10:59:32 +0530 Aneesh Kumar K V <aneesh.kumar@linux.ibm.com> wrote:
>
>> On 7/26/23 12:59 AM, Andrew Morton wrote:
>> > On Tue, 25 Jul 2023 00:37:46 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote:
>> >
>> >> This patch series implements changes required to support DAX vmemmap
>> >> optimization for ppc64.
>> >
>> > Do we have any measurements to help us understand the magnitude
>> > of this optimization?
>> >
>> > And any documentation which helps users understand whether and
>> > why they should enable this feature?
>>
>> That is memory space optimization due to kernel reusing the tail page struct pages. The details
>> of the optimization is documented in patch 11. We document there the impact with both 4k and
>> 64K page size.
>
> I suppose that with sufficient arithmetic one could use
> Documentation/powerpc/vmemmap_dedup.rst to figure out the bottom-line
> savings.
>
> I was more expecting a straightforward statement in the [0/N] overview
> to help people understand why they're reading this patchset at all.
> Like "saves 5% of total memory on my XXX machine".
This is specific to devdax usage and also depends on devdax alignment.
The actual saving details are also documented in mm/vmemmap_dedup.rst.
The saving will be based on the devdax device memory size and aligment.
With 64K page size for 16384 pages added (1G) we save 14 pages
With 4K page size for 262144 pages added (1G) we save 4094 pages
With 4K page size for 512 pages added (2M) we save 6 pages
-aneesh
next prev parent reply other threads:[~2023-07-27 5:38 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-24 19:07 [PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64 Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 01/13] mm/hugepage pud: Allow arch-specific helper function to check huge page pud support Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-26 10:52 ` [PATCH v6 01/13 -fix] " Aneesh Kumar K.V
2023-07-26 10:52 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 02/13] mm: Change pudp_huge_get_and_clear_full take vm_area_struct as arg Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 03/13] mm/vmemmap: Improve vmemmap_can_optimize and allow architectures to override Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 04/13] mm/vmemmap: Allow architectures to override how vmemmap optimization works Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 05/13] mm: Add pud_same similar to __HAVE_ARCH_P4D_SAME Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 06/13] mm/huge pud: Use transparent huge pud helpers only with CONFIG_TRANSPARENT_HUGEPAGE Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 07/13] mm/vmemmap optimization: Split hugetlb and devdax vmemmap optimization Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 08/13] powerpc/mm/trace: Convert trace event to trace event class Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 09/13] powerpc/book3s64/mm: Enable transparent pud hugepage Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 10/13] powerpc/book3s64/vmemmap: Switch radix to use a different vmemmap handling function Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-27 5:06 ` [PATCH v6 10/13 -fix] " Aneesh Kumar K.V
2023-07-27 5:06 ` Aneesh Kumar K.V
2023-07-28 10:22 ` [PATCH v6 10/13 -fix2] " Aneesh Kumar K.V
2023-07-28 10:22 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 11/13] powerpc/book3s64/radix: Add support for vmemmap optimization for radix Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-26 14:05 ` [PATCH v6 11/13 -fix] " Aneesh Kumar K.V
2023-07-26 14:05 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 12/13] powerpc/book3s64/radix: Remove mmu_vmemmap_psize Aneesh Kumar K.V
2023-07-28 10:23 ` [PATCH v6 12/13 -fix] " Aneesh Kumar K.V
2023-07-28 10:23 ` Aneesh Kumar K.V
2023-07-24 19:07 ` [PATCH v6 13/13] powerpc/book3s64/radix: Add debug message to give more details of vmemmap allocation Aneesh Kumar K.V
2023-07-24 19:07 ` Aneesh Kumar K.V
2023-07-25 19:29 ` [PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64 Andrew Morton
2023-07-25 19:29 ` Andrew Morton
2023-07-26 5:29 ` Aneesh Kumar K V
2023-07-26 5:29 ` Aneesh Kumar K V
2023-07-26 18:52 ` Andrew Morton
2023-07-26 18:52 ` Andrew Morton
2023-07-27 5:37 ` Aneesh Kumar K.V [this message]
2023-07-27 5:37 ` Aneesh Kumar K.V
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