On Thu, Nov 4, 2021 at 3:08 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Nov 04, 2021 at 02:46:35PM -0700, Mina Almasry wrote: > > Add PM_THP to allow userspace to detect whether a given virt address is > > currently mapped by a hugepage or not. > > Well, no, that's not what that means. > Sorry, that was the intention, but I didn't implement the intention correctly. > > @@ -1396,6 +1397,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm, > > flags |= PM_FILE; > > if (page && page_mapcount(page) == 1) > > flags |= PM_MMAP_EXCLUSIVE; > > + if (page && PageTransCompound(page)) > > + flags |= PM_THP; > > All that PageTransCompound() does is call PageCompound(). It doesn't > tell you if the underlying allocation is PMD sized, nor properly aligned. > > And you didn't answer my question about whether you want information about > whether a large page is being used that's not quite as large as a PMD. > Sorry, I thought the implementation would make it clear but I didn't do that correctly. Right now and for the foreseeable future what I want to know is whether the page is mapped by a PMD. All the below work for me: 1. Flag is set if the page is either a PMD size THP page. 2. Flag is set if the page is either a PMD size THP page or PMD size hugetlbfs page. 3. Flag is set if the page is either a PMD size THP page or PMD size hugetlbfs page or contig PTE size hugetlbfs page. I prefer #2 and I think it's maybe most extensible for future use cases that 1 flag tells whether the page is PMD hugepage and another flag is a large cont PTE page.
