On Thu, Apr 20, 2023 at 02:35:00PM -0700, Suren Baghdasaryan wrote: > On Thu, Apr 20, 2023 at 1:34 PM Carlos Llamas <cmllamas@xxxxxxxxxx> wrote: > > > > Instead of caching page pointers, I believe binder could make use of > > get_user_pages_remote() and trigger a page fault as needed. Basically, > > implement something similar to access_remote_vm() but that instead does > > a copy_from_user(). However, I don't see many in-tree users of these > > routines, so I wonder if I'm overlooking something in this approach? > > Sounds doable but there might be GUP details I'm missing... > > > > > One more reason for the page caching in binder is being able to free > > pages from the shrinker's callback. Unused pages are added to an LRU > > list and we manually zap/free them when they are reclaimed. It is not > > evident to me how can binder mark a range within the vma region as > > reclaimable? > > I think you would have to release the individual pages using > put_page(). Also note that get_user_pages_remote() is being > deprecated, see: > https://elixir.bootlin.com/linux/latest/source/mm/gup.c#L2171 Yeah, I remember reading that comment but it doesn't make sense since the suggested alternatives do not support operations on _remote_ mm. I actually tracked this down and it seems the original comment was made for get_user_pages() instead, in commit f0818f472d8d ("mm: gup: add get_user_pages_locked and get_user_pages_unlocked"). The whole comment block was then carried over without update into get_user_pages_remote() in commit 1e9877902dc7 ("mm/gup: Introduce get_user_pages_remote()"). The comment block was finally switched to use the "_remote" portion in commit adc8cb406e52 ("mm/gup.c: update the documentation"). In reality, this comment should be relocated to the get_user_pages() section. > > > > > Any pointers are appreciated! > > > > -- > > Carlos Llamas
