Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup

From	Jungseok Lee <jungseoklee85@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup
Date	2015-11-03 15:20 +0100
Message-ID	<qqKBk-3MG-15@gated-at.bofh.it> (permalink)
References	<qpVyN-5qp-3@gated-at.bofh.it> <qpVyN-5qp-1@gated-at.bofh.it> <qqpZU-7ux-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Nov 3, 2015, at 1:10 AM, Christoph Lameter wrote:

Dear Christoph,

> On Sun, 1 Nov 2015, Jungseok Lee wrote:
> 
>> There is no room to adjust 'atom_size' now when a generic percpu area
>> is used. It would be redundant to write down an architecture-specific
>> setup_per_cpu_areas() in order to only change the 'atom_size'. Thus,
>> this patch adds a new definition, PERCPU_ATOM_SIZE, which is PAGE_SIZE
>> by default. The value could be updated if needed by architecture.
> 
> What is atom_size? Why would you want a difference allocation size here?
> The percpu area is virtually mapped regardless. So you will have
> contiguous addresses even without atom_size.

I think Catalin have already written down a perfect explanation. I'd like
memory with an alignment greater than PAGE_SIZE. But, __per_cpu_offset[]
is PAGE_SIZE aligned under a generic setup_per_cpu_areas(). That is,
secondary cores cannot get that kind of space.

Thanks for taking a look at this doubtable change!

Best Regards
Jungseok Lee
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-01 08:50 +0100
  Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Christoph Lameter <cl@linux.com> - 2015-11-02 17:20 +0100
    Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Catalin Marinas <catalin.marinas@arm.com> - 2015-11-02 17:30 +0100
      Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Christoph Lameter <cl@linux.com> - 2015-11-02 17:50 +0100
        Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Catalin Marinas <catalin.marinas@arm.com> - 2015-11-02 18:40 +0100
          Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Christoph Lameter <cl@linux.com> - 2015-11-02 19:20 +0100
            Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup Catalin Marinas <catalin.marinas@arm.com> - 2015-11-02 19:40 +0100
      Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-03 15:00 +0100
        Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu  area setup James Morse <james.morse@arm.com> - 2015-11-03 19:00 +0100
          Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-04 14:40 +0100
    Re: [PATCH v6 2/3] percpu: add PERCPU_ATOM_SIZE for a generic percpu area setup Jungseok Lee <jungseoklee85@gmail.com> - 2015-11-03 15:20 +0100

csiph-web