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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 13:58:00 +0900	[thread overview]
Message-ID: <4FAB4AD8.2010200@kernel.org> (raw)
In-Reply-To: <001501cd2e4d$c7dbc240$579346c0$%dae@samsung.com>

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.

-- 
Kind regards,
Minchan Kim

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  reply	other threads:[~2012-05-10  4:57 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 [this message]
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
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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