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From: Minchan Kim <minchan@kernel.org>
To: Inki Dae <inki.dae@samsung.com>
Cc: 'Jerome Glisse' <j.glisse@gmail.com>,
	airlied@linux.ie, dri-devel@lists.freedesktop.org,
	kyungmin.park@samsung.com, sw0312.kim@samsung.com,
	linux-mm@kvack.org
Subject: Re: [PATCH 2/2 v3] drm/exynos: added userptr feature.
Date: Thu, 10 May 2012 16:05:51 +0900	[thread overview]
Message-ID: <4FAB68CF.8000404@kernel.org> (raw)
In-Reply-To: <002401cd2e7a$1e8b0ed0$5ba12c70$%dae@samsung.com>

On 05/10/2012 03:57 PM, Inki Dae wrote:

> 
> 
>> -----Original Message-----
>> From: Minchan Kim [mailto:minchan@kernel.org]
>> Sent: Thursday, May 10, 2012 1:58 PM
>> To: Inki Dae
>> Cc: 'Jerome Glisse'; airlied@linux.ie; dri-devel@lists.freedesktop.org;
>> kyungmin.park@samsung.com; sw0312.kim@samsung.com; linux-mm@kvack.org
>> Subject: Re: [PATCH 2/2 v3] drm/exynos: added userptr feature.
>>
>> On 05/10/2012 10:39 AM, Inki Dae wrote:
>>
>>> Hi Jerome,
>>>
>>>> -----Original Message-----
>>>> From: Jerome Glisse [mailto:j.glisse@gmail.com]
>>>> Sent: Wednesday, May 09, 2012 11:46 PM
>>>> To: Inki Dae
>>>> Cc: airlied@linux.ie; dri-devel@lists.freedesktop.org;
>>>> kyungmin.park@samsung.com; sw0312.kim@samsung.com; linux-mm@kvack.org
>>>> Subject: Re: [PATCH 2/2 v3] drm/exynos: added userptr feature.
>>>>
>>>> On Wed, May 9, 2012 at 2:17 AM, Inki Dae <inki.dae@samsung.com> wrote:
>>>>> this feature is used to import user space region allocated by malloc()
>>>> or
>>>>> mmaped into a gem. and to guarantee the pages to user space not to be
>>>>> swapped out, the VMAs within the user space would be locked and then
>>>> unlocked
>>>>> when the pages are released.
>>>>>
>>>>> but this lock might result in significant degradation of system
>>>> performance
>>>>> because the pages couldn't be swapped out so we limit user-desired
>>>> userptr
>>>>> size to pre-defined.
>>>>>
>>>>> Signed-off-by: Inki Dae <inki.dae@samsung.com>
>>>>> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
>>>>
>>>>
>>>> Again i would like feedback from mm people (adding cc). I am not sure
>>>
>>> Thank you, I missed adding mm as cc.
>>>
>>>> locking the vma is the right anwser as i said in my previous mail,
>>>> userspace can munlock it in your back, maybe VM_RESERVED is better.
>>>
>>> I know that with VM_RESERVED flag, also we can avoid the pages from
>> being
>>> swapped out. but these pages should be unlocked anytime we want because
>> we
>>> could allocate all pages on system and lock them, which in turn, it may
>>> result in significant deterioration of system performance.(maybe other
>>> processes requesting free memory would be blocked) so I used VM_LOCKED
>> flags
>>> instead. but I'm not sure this way is best also.
>>>
>>>> Anyway even not considering that you don't check at all that process
>>>> don't go over the limit of locked page see mm/mlock.c RLIMIT_MEMLOCK
>>>
>>> Thank you for your advices.
>>>
>>>> for how it's done. Also you mlock complete vma but the userptr you get
>>>> might be inside say 16M vma and you only care about 1M of userptr, if
>>>> you mark the whole vma as locked than anytime a new page is fault in
>>>> the vma else where than in the buffer you are interested then it got
>>>> allocated for ever until the gem buffer is destroy, i am not sure of
>>>> what happen to the vma on next malloc if it grows or not (i would
>>>> think it won't grow at it would have different flags than new
>>>> anonymous memory).
>>
>>
>> I don't know history in detail because you didn't have sent full patches
>> to linux-mm and
>> I didn't read the below code, either.
>> Just read your description and reply of Jerome. Apparently, there is
>> something I missed.
>>
>> Your goal is to avoid swap out some user pages which is used in kernel at
>> the same time. Right?
>> Let's use get_user_pages. Is there any issue you can't use it?
>> It increases page count so reclaimer can't swap out page.
>> Isn't it enough?
>> Marking whole VMA into MLCOKED is overkill.
>>
> 
> As I mentioned, we are already using get_user_pages. as you said, this
> function increases page count but just only things to the user address space
> cpu already accessed. other would be allocated by page fault hander once
> get_user_pages call. if so... ok, after that refcount(page->_count) of the


Not true. Look __get_user_pages.
It handles case you mentioned by handle_mm_fault.
Do I miss something?

> pages user already accessed would have 2 and just 1 for other all pages. so
> we may have to consider only pages never accessed by cpu to be locked to
> avoid from swapped out.
> 
> Thanks,
> Inki Dae
> 
>> --
>> Kind regards,
>> Minchan Kim
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
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> 



-- 
Kind regards,
Minchan Kim

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2012-05-10  7:05 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1335188594-17454-4-git-send-email-inki.dae@samsung.com>
     [not found] ` <1336544259-17222-1-git-send-email-inki.dae@samsung.com>
     [not found]   ` <1336544259-17222-3-git-send-email-inki.dae@samsung.com>
2012-05-09 14:45     ` [PATCH 2/2 v3] drm/exynos: added userptr feature Jerome Glisse
2012-05-09 18:32       ` Jerome Glisse
2012-05-10  2:44         ` Inki Dae
2012-05-10 15:05           ` Jerome Glisse
2012-05-10 15:31             ` Daniel Vetter
2012-05-10 15:52               ` Jerome Glisse
2012-05-11  1:47                 ` Inki Dae
2012-05-11  2:08                   ` Minchan Kim
2012-05-10  1:39       ` Inki Dae
2012-05-10  4:58         ` Minchan Kim
2012-05-10  6:53           ` KOSAKI Motohiro
2012-05-10  7:27             ` Minchan Kim
2012-05-10  7:31               ` Kyungmin Park
2012-05-10  7:56                 ` Minchan Kim
2012-05-10  7:58                   ` Minchan Kim
2012-05-10  6:57           ` Inki Dae
2012-05-10  7:05             ` Minchan Kim [this message]
2012-05-10  7:59               ` InKi Dae
2012-05-10  8:11                 ` Minchan Kim
2012-05-10  8:44                   ` Inki Dae
2012-05-10 17:53                     ` KOSAKI Motohiro
2012-05-11  0:50                       ` Minchan Kim
2012-05-11  2:51                         ` KOSAKI Motohiro
2012-05-11  3:01                           ` Jerome Glisse
2012-05-11 21:20                             ` KOSAKI Motohiro
2012-05-11 22:22                               ` Jerome Glisse
2012-05-11 22:59                                 ` KOSAKI Motohiro
2012-05-11 23:29                                   ` Jerome Glisse
2012-05-11 23:39                                     ` KOSAKI Motohiro
2012-05-12  4:48                                       ` InKi Dae
2012-05-14  4:29                                         ` Minchan Kim
     [not found]   ` <1336976268-14328-1-git-send-email-inki.dae@samsung.com>
2012-05-14  8:12     ` [PATCH 0/2 v4] " Inki Dae
     [not found]     ` <1336976268-14328-2-git-send-email-inki.dae@samsung.com>
2012-05-14  8:12       ` [PATCH 1/2 v4] drm/exynos: added userptr limit ioctl Inki Dae
     [not found]     ` <1336976268-14328-3-git-send-email-inki.dae@samsung.com>
     [not found]       ` <CAHGf_=qv45_uuO_JWMXOQp4VymyOxVq76rGXghoNMmDh7mURKQ@mail.gmail.com>
     [not found]         ` <003001cd319e$263c9230$72b5b690$%dae@samsung.com>
     [not found]           ` <4FB0AE87.60800@gmail.com>
2012-05-14  8:13             ` [PATCH 2/2 v4] drm/exynos: added userptr feature Inki Dae
     [not found]       ` <CAH3drwb13T2RXgEuauGchoZUDAgL+wrv3SR66sZNyGk_6tRTFw@mail.gmail.com>
2012-05-15  4:33         ` Inki Dae
2012-05-15 14:31           ` Jerome Glisse
2012-05-16  8:49             ` Inki Dae

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