On 8/31/21 03:56, Miaohe Lin wrote: > On 2021/8/30 22:24, Matthew Wilcox wrote: >> On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote: >>> Don't use with __GFP_HIGHMEM because page_address() cannot represent >>> highmem pages without kmap(). Newly allocated pages would leak as >>> page_address() will return NULL for highmem pages here. But It works >>> now because the only caller does not specify __GFP_HIGHMEM now. >> >> This is a misunderstanding of how alloc_pages_exact() / >> alloc_pages_exact_nid() work. You simply can't call them with >> GFP_HIGHMEM. >> > > Yep, they can't work with GFP_HIGHMEM. So IMO it might be better to > get rid of GFP_HIGHMEM explicitly or add a comment to clarify this > situation to avoid future misbehavior. But this may be a unnecessary > worry... Do you prefer to not change anything here? I agree with the suggestion below... > Many thanks. > >> If you really must change anything here, >> s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both >> alloc_pages_exact() and alloc_pages_exact_nid(). ... which means __GFP_HIGHMEM would be stripped and additionally there would be a warning.
