On 05/10/2012 04:59 PM, InKi Dae wrote: > 2012/5/10, Minchan Kim <minchan@xxxxxxxxxx>: >> On 05/10/2012 03:57 PM, Inki Dae wrote: >> >>> >>> >>>> -----Original Message----- >>>> From: Minchan Kim [mailto:minchan@xxxxxxxxxx] >>>> Sent: Thursday, May 10, 2012 1:58 PM >>>> To: Inki Dae >>>> Cc: 'Jerome Glisse'; 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 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? >>>> 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? >> > > let's assume that one application want to allocate user space memory > region using malloc() and then write something on the region. as you > may know, user space buffer doen't have real physical pages once > malloc() call so if user tries to access the region then page fault > handler would be triggered Understood. > and then in turn next process like swap in to fill physical frame number into entry of the page faulted. Sorry, I can't understand your point due to my poor English. Could you rewrite it easiliy? :) Thanks. > of course,if user never access the buffer and requested userptr then > handle_mm_fault would be called by __get_user_pages. please give me > any comments if there is my missing point. > > Thanks, > Inki Dae > > >>> 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@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> >>> >> >> >> >> -- >> 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> >> > > -- > 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> > -- 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>