On 05/10/2012 03:53 PM, KOSAKI Motohiro wrote: > (5/10/12 12:58 AM), Minchan Kim wrote: >> On 05/10/2012 10:39 AM, Inki Dae wrote: >> >>> Hi Jerome, >>> >>>> -----Original Message----- >>>> From: Jerome Glisse [mailto:j.glisse@xxxxxxxxx] >>>> Sent: Wednesday, May 09, 2012 11:46 PM >>>> To: Inki Dae >>>> Cc: airlied@xxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; >>>> kyungmin.park@xxxxxxxxxxx; sw0312.kim@xxxxxxxxxxx; linux-mm@xxxxxxxxx >>>> Subject: Re: [PATCH 2/2 v3] drm/exynos: added userptr feature. >>>> >>>> On Wed, May 9, 2012 at 2:17 AM, Inki Dae<inki.dae@xxxxxxxxxxx> 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@xxxxxxxxxxx> >>>>> Signed-off-by: Kyungmin Park<kyungmin.park@xxxxxxxxxxx> >>>> >>>> >>>> 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? > > Maybe because get_user_pages() is fork unsafe? dunno. If there is such problem, I think user program should handle it by MADV_DONTFORK and make to allow write by only parent process. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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@xxxxxxxxx";> email@xxxxxxxxx </a>