Re: [PATCH 2/2 v3] drm/exynos: added userptr feature.

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(5/10/12 8:50 PM), Minchan Kim wrote:
Hi KOSAKI,

On 05/11/2012 02:53 AM, KOSAKI Motohiro wrote:

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? :)


Simply saying, handle_mm_fault would be called to update pte after
finding
vma and checking access right. and as you know, there are many cases to
process page fault such as COW or demand paging.

Hmm. If I understand correctly, you guys misunderstand mlock. it doesn't
page pinning
nor prevent pfn change. It only guarantee to don't make swap out. e.g.


Symantic point of view, you're right but the implementation makes sure page pinning.

memory campaction
feature may automatically change page physical address.


I tried it last year but decided drop by realtime issue.
https://lkml.org/lkml/2011/8/29/295

so I think mlock is a kind of page pinning. If elsewhere I don't realized is doing, that place should be fixed.
Or my above patch should go ahead.

Thanks pointing out. I didn't realized your patch didn't merged. I think it should go ahead. think autonuma case,
if mlock disable autonuma migration, that's bug.  I don't think we can promise mlock don't change physical page.
I wonder if any realtime guys page migration is free lunch. they should disable both auto migration and compaction.

And, think if application explictly use migrate_pages(2) or admins uses cpusets. driver code can't assume such scenario
doesn't occur, yes?


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