Messages in this thread | | | Subject | Re: [PATCH 1/5] mm: Introduce mm_struct.has_pinned | From | John Hubbard <> | Date | Mon, 21 Sep 2020 17:01:19 -0700 |
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On 9/21/20 4:53 PM, John Hubbard wrote: > 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*()
arggh, correction: please make that:
"...whether or not a page is part of an mm struct that...".
(Present tense.) Otherwise, people start wondering about the checkered past of a page's past lives, and it badly distracts from the main point here. :)
thanks, -- John Hubbard NVIDIA
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