> -----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 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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
