On 9/22/20 3:33 AM, Jan Kara wrote:
On Mon 21-09-20 23:41:16, John Hubbard wrote:
On 9/21/20 2:20 PM, Peter Xu wrote:
...
+ if (unlikely(READ_ONCE(src_mm->has_pinned) &&
+ page_maybe_dma_pinned(src_page))) {
This condition would make a good static inline function. It's used in 3
places, and the condition is quite special and worth documenting, and
having a separate function helps with that, because the function name
adds to the story. I'd suggest approximately:
page_likely_dma_pinned()
for the name.
Well, but we should also capture that this really only works for anonymous
pages. For file pages mm->has_pinned does not work because the page may be
still pinned by completely unrelated process as Jann already properly
pointed out earlier in the thread. So maybe anon_page_likely_pinned()?
Possibly also assert PageAnon(page) in it if we want to be paranoid...
Honza
The file-backed case doesn't really change anything, though:
page_maybe_dma_pinned() is already a "fuzzy yes" in the same sense: you
can get a false positive. Just like here, with an mm->has_pinned that
could be a false positive for a process.
And for that reason, I'm also not sure an "assert PageAnon(page)" is
desirable. That assertion would prevent file-backed callers from being
able to call a function that provides a fuzzy answer, but I don't see
why you'd want or need to do that. The goal here is to make the fuzzy
answer a little bit more definite, but it's not "broken" just because
the result is still fuzzy, right?
Apologies if I'm missing a huge point here... :)
thanks,
--
John Hubbard
NVIDIA
