From: Keith Busch <keith.busch@intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Kirill Shutemov <kirill.shutemov@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH 0/7] mm: faster get user pages
Date: Wed, 19 Sep 2018 16:26:22 -0600 [thread overview]
Message-ID: <20180919222621.GA29003@localhost.localdomain> (raw)
In-Reply-To: <40b392d0-0642-2d9b-5325-664a328ff677@intel.com>
On Wed, Sep 19, 2018 at 02:15:28PM -0700, Dave Hansen wrote:
> On 09/19/2018 02:02 PM, Keith Busch wrote:
> > Pinning user pages out of nvdimm dax memory is significantly slower
> > compared to system ram. Analysis points to software overhead incurred
> > from a radix tree lookup. This patch series fixes that by removing the
> > relatively costly dev_pagemap lookup that was repeated for each page,
> > significantly increasing gup time.
>
> Could you also remind us why DAX pages are such special snowflakes and
> *require* radix tree lookups in the first place?
Yeah, ZONE_DEVICE memory is special. It has struct page mappings, but
not for online general use. The dev_pagemap is the metadata to the zone
device memory, and that metadata is stashed in a radix tree.
We're looking up the dev_pagemap in this path to take a reference so
the zone device can't be unmapped.
next prev parent reply other threads:[~2018-09-19 22:26 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 21:02 [PATCH 0/7] mm: faster get user pages Keith Busch
2018-09-19 21:02 ` [PATCH 1/7] mm/gup_benchmark: Time put_page Keith Busch
2018-09-19 21:02 ` [PATCH 2/7] mm/gup_benchmark: Add additional pinning methods Keith Busch
2018-09-19 21:02 ` [PATCH 3/7] tools/gup_benchmark: Fix 'write' flag usage Keith Busch
2018-09-19 21:02 ` [PATCH 4/7] tools/gup_benchmark: Allow user specified file Keith Busch
2018-09-19 21:02 ` [PATCH 5/7] tools/gup_benchmark: Add parameter for hugetlb Keith Busch
2018-09-19 21:02 ` [PATCH 6/7] mm/gup: Combine parameters into struct Keith Busch
2018-09-19 22:40 ` Keith Busch
2018-09-21 2:34 ` kbuild test robot
2018-09-21 2:34 ` kbuild test robot
2018-09-21 2:58 ` kbuild test robot
2018-09-21 2:58 ` kbuild test robot
2018-09-19 21:02 ` [PATCH 7/7] mm/gup: Cache dev_pagemap while pinning pages Keith Busch
2018-09-19 21:15 ` [PATCH 0/7] mm: faster get user pages Dave Hansen
2018-09-19 22:26 ` Keith Busch [this message]
2018-09-19 22:27 ` Dan Williams
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