From: Dan Williams <dan.j.williams@intel.com>
To: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Ingo Molnar <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>, Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Logan Gunthorpe <logang@deltatee.com>,
Kirill Shutemov <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference
Date: Sun, 30 Apr 2017 19:40:25 -0700 [thread overview]
Message-ID: <CAPcyv4hnDDeAZDEH_8=1xZY99pTW+wh8V714jLEg5J-s2NW6rw@mail.gmail.com> (raw)
In-Reply-To: <20170501015403.GA16181@redhat.com>
On Sun, Apr 30, 2017 at 6:54 PM, Jerome Glisse <jglisse@redhat.com> wrote:
> On Sun, Apr 30, 2017 at 06:42:02PM -0700, Dan Williams wrote:
>> On Sun, Apr 30, 2017 at 4:14 PM, Jerome Glisse <jglisse@redhat.com> wrote:
>> > On Sat, Apr 29, 2017 at 01:17:26PM +0300, Kirill A. Shutemov wrote:
>> >> On Fri, Apr 28, 2017 at 03:33:07PM -0400, Jerome Glisse wrote:
>> >> > On Fri, Apr 28, 2017 at 12:22:24PM -0700, Dan Williams wrote:
>> >> > > Are you sure about needing to hook the 2 -> 1 transition? Could we
>> >> > > change ZONE_DEVICE pages to not have an elevated reference count when
>> >> > > they are created so you can keep the HMM references out of the mm hot
>> >> > > path?
>> >> >
>> >> > 100% sure on that :) I need to callback into driver for 2->1 transition
>> >> > no way around that. If we change ZONE_DEVICE to not have an elevated
>> >> > reference count that you need to make a lot more change to mm so that
>> >> > ZONE_DEVICE is never use as fallback for memory allocation. Also need
>> >> > to make change to be sure that ZONE_DEVICE page never endup in one of
>> >> > the path that try to put them back on lru. There is a lot of place that
>> >> > would need to be updated and it would be highly intrusive and add a
>> >> > lot of special cases to other hot code path.
>> >>
>> >> Could you explain more on where the requirement comes from or point me to
>> >> where I can read about this.
>> >>
>> >
>> > HMM ZONE_DEVICE pages are use like other pages (anonymous or file back page)
>> > in _any_ vma. So i need to know when a page is freed ie either as result of
>> > unmap, exit or migration or anything that would free the memory. For zone
>> > device a page is free once its refcount reach 1 so i need to catch refcount
>> > transition from 2->1
>> >
>> > This is the only way i can inform the device that the page is now free. See
>> >
>> > https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v21&id=52da8fe1a088b87b5321319add79e43b8372ed7d
>> >
>> > There is _no_ way around that.
>>
>> Ok, but I need to point out that this not a ZONE_DEVICE requirement.
>> This is an HMM-specific need. So, this extra reference counting should
>> be clearly delineated as part of the MEMORY_DEVICE_PRIVATE use case.
>
> And it already is delimited, i think you even gave your review by on
> the patch.
>
I gave my reviewed-by to the patch that leveraged
{get,put}_zone_device_page(), but now those are gone and HMM needs a
new patch. I'm just saying these reference counts should not come back
as {get,put}_zone_device_page() because now they're HMM specific.
>> Can we hide the extra reference counting behind a static branch so
>> that the common case fast path doesn't get slower until a HMM device
>> shows up?
>
> Like i already did With likely()/unlikely() ? Or something else ?
>
> https://cgit.freedesktop.org/~glisse/linux/commit/?h=hmm-v21&id=e84778e9db0672e371eb6599dfcb812512118842
Something different:
http://lxr.free-electrons.com/source/Documentation/static-keys.txt
next prev parent reply other threads:[~2017-05-01 2:40 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-20 21:46 [tip:x86/mm] x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation Dan Williams
2017-04-21 14:16 ` Kirill A. Shutemov
2017-04-21 19:30 ` Dan Williams
2017-04-23 9:52 ` [PATCH] Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation" Ingo Molnar
2017-04-23 23:31 ` get_zone_device_page() in get_page() and page_cache_get_speculative() Kirill A. Shutemov
2017-04-24 17:23 ` Dan Williams
2017-04-24 17:30 ` Kirill A. Shutemov
2017-04-24 17:47 ` Dan Williams
2017-04-24 18:01 ` Kirill A. Shutemov
2017-04-24 18:25 ` Kirill A. Shutemov
2017-04-24 18:41 ` Dan Williams
2017-04-25 13:19 ` Kirill A. Shutemov
2017-04-25 16:44 ` Dan Williams
2017-04-27 0:55 ` [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Dan Williams
2017-04-27 8:33 ` Kirill A. Shutemov
2017-04-28 6:39 ` Ingo Molnar
2017-04-28 8:14 ` [PATCH] mm, zone_device: Replace " Kirill A. Shutemov
2017-04-28 17:23 ` [PATCH v2] mm, zone_device: replace " Dan Williams
2017-04-28 17:34 ` Jerome Glisse
2017-04-28 17:41 ` Dan Williams
2017-04-28 18:00 ` Jerome Glisse
2017-04-28 19:02 ` Dan Williams
2017-04-28 19:16 ` Jerome Glisse
2017-04-28 19:22 ` Dan Williams
2017-04-28 19:33 ` Jerome Glisse
2017-04-29 10:17 ` Kirill A. Shutemov
2017-04-30 23:14 ` Jerome Glisse
2017-05-01 1:42 ` Dan Williams
2017-05-01 1:54 ` Jerome Glisse
2017-05-01 2:40 ` Dan Williams [this message]
2017-05-01 3:48 ` Logan Gunthorpe
2017-05-01 10:23 ` Kirill A. Shutemov
2017-05-01 13:55 ` Jerome Glisse
2017-05-01 20:19 ` Dan Williams
2017-05-01 20:32 ` Jerome Glisse
2017-05-02 11:37 ` Kirill A. Shutemov
2017-05-02 13:22 ` Jerome Glisse
2017-04-29 14:18 ` Ingo Molnar
2017-05-01 2:45 ` Dan Williams
2017-05-01 7:12 ` Ingo Molnar
2017-05-01 9:33 ` Kirill A. Shutemov
2017-05-01 8:28 ` [tip:x86/mm] mm, zone_device: Replace {get, put}_zone_device_page() with a single reference to fix pmem crash tip-bot for Dan Williams
2017-04-27 16:11 ` [PATCH] mm, zone_device: replace {get, put}_zone_device_page() with a single reference Logan Gunthorpe
2017-04-27 16:14 ` Dan Williams
2017-04-27 16:33 ` Logan Gunthorpe
2017-04-27 16:38 ` Dan Williams
2017-04-27 16:45 ` Logan Gunthorpe
2017-04-27 16:46 ` Dan Williams
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