linux-kernel - Re: [PATCH v2 1/5] pmem, dax: clean up clear

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Message-ID: <x49a8r2aes5.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 28 Oct 2015 17:01:30 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Jens Axboe <axboe@...com>, Jan Kara <jack@...e.cz>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	david <david@...morbit.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/5] pmem, dax: clean up clear_pmem()

Dan Williams <dan.j.williams@...el.com> writes:

> On Thu, Oct 22, 2015 at 1:48 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
>> Dan Williams <dan.j.williams@...el.com> writes:
>>
>>> Both, __dax_pmd_fault, and clear_pmem() were taking special steps to
>>> clear memory a page at a time to take advantage of non-temporal
>>> clear_page() implementations.  However, x86_64 does not use
>>> non-temporal instructions for clear_page(), and arch_clear_pmem() was
>>> always incurring the cost of __arch_wb_cache_pmem().
>>>
>>> Clean up the assumption that doing clear_pmem() a page at a time is more
>>> performant.
>>
>> Wouldn't another solution be to actually use non-temporal stores?
>
> Sure.
>
>> Why did you choose to punt?
>
> Just a priority call at this point.  Patches welcome of course ;-).

OK.  Patch is harmless.

Reviewed-by: Jeff Moyer <jmoyer@...hat.com>
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