Dan Williams <dan.j.williams@xxxxxxxxx> writes: [...] >> >> > > How on earth can a free'd page have both a 0 and 1 refcount?? >> >> > >> >> > This is residual wonkiness from memremap_pages() handing out pages with >> >> > elevated reference counts at the outset. >> >> >> >> I think the answer to my question is the above troubled code where we >> >> still set the page refcount back to 1 even in the page_free path, so >> >> there is some consistency "a freed paged may have a refcount of 1" for >> >> the driver. >> >> >> >> So, I guess this patch makes sense but I would put more noise around >> >> INIT_PAGEMAP_BUSY (eg annotate every driver that is using it with the >> >> explicit constant) and alert people that they need to fix their stuff >> >> to get rid of it. >> > >> > Sounds reasonable. >> > >> >> We should definately try to fix hmm_test as well so people have a good >> >> reference code to follow in fixing the other drivers :( >> > >> > Oh, that's a good idea. I can probably fix that up and leave it to the >> > GPU driver folks to catch up with that example so we can kill off >> > INIT_PAGEMAP_BUSY. >> >> I'm hoping to send my series that fixes up all drivers using device >> coherent/private later this week or early next. So you could also just >> wait for that and remove INIT_PAGEMAP_BUSY entirely. > > Oh, perfect, thanks! See https://lore.kernel.org/linux-mm/3d74bb439723c7e46cbe47d1711795308aee4ae3.1664171943.git-series.apopple@xxxxxxxxxx/ I already had this in a series because the change was motivated by a later patch there, but it's a standalone change and there's no reason it couldn't be split out into it's own patch if that's better for you. - Alistair
