Messages in this thread | | | From | Ross Dickson <> | Subject | Re: locking user space memory in kernel | Date | Thu, 8 Apr 2004 16:20:11 +1000 |
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Libor Michalek wrote:
>----- Forwarded message from Manfred Spraul <manfred@colorfullife.com> ----- > > >>Date: Sun, 21 Mar 2004 12:31:59 +0100 >>From: Manfred Spraul <manfred@colorfullife.com> >>To: Eli Cohen <mlxk@mellanox.co.il> >>Cc: linux-kernel@vger.kernel.org >>Subject: Re: locking user space memory in kernel >> >>Hi Eli, >> >>I think just get_user_pages() should be sufficient: the pages won't be >>swapped out. You don't need to set VM_LOCKED in vma->vm_flags to prevent >>the swap out. In the worst case, the pte is cleared a that will cause a >>soft page fault, but the physical address won't change. Multiple >>get_user_pages() calls on overlapping regions are ok, the page count is >>an atomic_t, at least 24-bit large. >> >> > > The soft page fault is a problem if the device is going to write data >into the buffer and then notify the user that the buffer now contains >valid data. If the soft page fault occurs before the device has written >to the page list, once the user is notified of the write and reads the >buffer, it will no longer be the same pages as the ones to which the >device wrote. >
I know of an open source driver for image acquisition cards iti-fg that does "PAGEWISE transfer of image frames directly into user space". The release notes mention the memory locking.
It is available here http://oss.gom.com/
Regards Ross.
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