On 9/21/20 2:17 PM, Peter Xu wrote:
(Commit message collected from Jason Gunthorpe)
Reduce the chance of false positive from page_maybe_dma_pinned() by keeping
Not yet, it doesn't. :) More:
track if the mm_struct has ever been used with pin_user_pages(). mm_structs
that have never been passed to pin_user_pages() cannot have a positive
page_maybe_dma_pinned() by definition. This allows cases that might drive up
the page ref_count to avoid any penalty from handling dma_pinned pages.
Due to complexities with unpining this trivial version is a permanent sticky
bit, future work will be needed to make this a counter.
How about this instead:
Subsequent patches intend to reduce the chance of false positives from
page_maybe_dma_pinned(), by also considering whether or not a page has
even been part of an mm struct that has ever had pin_user_pages*()