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

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Message-ID: <CAPcyv4jGPaoZAHSUqWg+2yqN=jCBTEivJauKa-Mr58cFkDF+CQ@mail.gmail.com>
Date:	Thu, 22 Oct 2015 15:29:33 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jeff Moyer <jmoyer@...hat.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@...r.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()

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 ;-).
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