linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Will Deacon <will@kernel.org>,
	Sudarshan Rajagopalan <sudaraja@codeaurora.org>
Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	David Hildenbrand <david@redhat.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Steven Price <steven.price@arm.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH 1/1] arm64/sparsemem: reduce SECTION_SIZE_BITS
Date: Fri, 22 Jan 2021 08:28:03 +0530	[thread overview]
Message-ID: <38f15b8e-6cb8-e28b-fb32-15a5312aa8e3@arm.com> (raw)
In-Reply-To: <20210121133652.GA22341@willie-the-truck>



On 1/21/21 7:06 PM, Will Deacon wrote:
> On Wed, Jan 20, 2021 at 09:29:13PM -0800, Sudarshan Rajagopalan wrote:
>> memory_block_size_bytes() determines the memory hotplug granularity i.e the
>> amount of memory which can be hot added or hot removed from the kernel. The
>> generic value here being MIN_MEMORY_BLOCK_SIZE (1UL << SECTION_SIZE_BITS)
>> for memory_block_size_bytes() on platforms like arm64 that does not override.
>>
>> Current SECTION_SIZE_BITS is 30 i.e 1GB which is large and a reduction here
>> increases memory hotplug granularity, thus improving its agility. A reduced
>> section size also reduces memory wastage in vmemmmap mapping for sections
>> with large memory holes. So we try to set the least section size as possible.
>>
>> A section size bits selection must follow:
>> (MAX_ORDER - 1 + PAGE_SHIFT) <= SECTION_SIZE_BITS
>>
>> CONFIG_FORCE_MAX_ZONEORDER is always defined on arm64 and so just following it
>> would help achieve the smallest section size.
>>
>> SECTION_SIZE_BITS = (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT)
>>
>> SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB   for 4K pages
>> SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB  for 16K pages without THP
>> SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB  for 16K pages with THP
>> SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB  for 64K pages without THP
>> SECTION_SIZE_BITS = 29 (14 - 1 + 16) i.e 512MB for 64K pages with THP
>>
>> But there are other problems in reducing SECTION_SIZE_BIT. Reducing it by too
>> much would over populate /sys/devices/system/memory/ and also consume too many
>> page->flags bits in the !vmemmap case. Also section size needs to be multiple
>> of 128MB to have PMD based vmemmap mapping with CONFIG_ARM64_4K_PAGES.
>>
>> Given these constraints, lets just reduce the section size to 128MB for 4K
>> and 16K base page size configs, and to 512MB for 64K base page size config.
>>
>> Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
>> Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Mike Rapoport <rppt@linux.ibm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Steven Price <steven.price@arm.com>
>> Cc: Suren Baghdasaryan <surenb@google.com>
>> ---
>>  arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++--
>>  1 file changed, 21 insertions(+), 2 deletions(-)
> 
> Anshuman -- are you happy with this now?

Yes.

A small nit. There are couple of extra lines in the patch which
can be dropped, probably while merging.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>


  reply	other threads:[~2021-01-22  2:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21  5:29 [PATCH 0/1] " Sudarshan Rajagopalan
2021-01-21  5:29 ` [PATCH 1/1] " Sudarshan Rajagopalan
2021-01-21 10:08   ` Christoph Lameter
2021-01-21 15:54     ` Catalin Marinas
2021-01-21 13:36   ` Will Deacon
2021-01-22  2:58     ` Anshuman Khandual [this message]
2021-01-21 13:45   ` David Hildenbrand
2021-01-21 14:16   ` Mike Rapoport
2021-01-21 16:04     ` David Hildenbrand
2021-01-21 15:51   ` Catalin Marinas
2021-01-21 18:26 ` [PATCH 0/1] " Will Deacon
2021-01-29  0:17   ` Pavel Tatashin

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=38f15b8e-6cb8-e28b-fb32-15a5312aa8e3@arm.com \
    --to=anshuman.khandual@arm.com \
    --cc=akpm@linux-foundation.org \
    --cc=catalin.marinas@arm.com \
    --cc=david@redhat.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=logang@deltatee.com \
    --cc=mark.rutland@arm.com \
    --cc=rppt@linux.ibm.com \
    --cc=steven.price@arm.com \
    --cc=sudaraja@codeaurora.org \
    --cc=surenb@google.com \
    --cc=will@kernel.org \
    --subject='Re: [PATCH 1/1] arm64/sparsemem: reduce SECTION_SIZE_BITS' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).