On Tue, Mar 09, 2021 at 11:14:58PM +1100, Alistair Popple wrote:
-static inline struct page *migration_entry_to_page(swp_entry_t entry) -{
- struct page *p = pfn_to_page(swp_offset(entry));
- /*
* Any use of migration entries may only occur while the* corresponding page is locked*/- BUG_ON(!PageLocked(compound_head(p)));
- return p;
-}
+static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry) +{
- struct page *p = pfn_to_page(swp_offset(entry));
- /*
* Any use of migration entries may only occur while the* corresponding page is locked*/- BUG_ON(is_migration_entry(entry) && !PageLocked(compound_head(p)));
- return p;
+}
I appreciate you're only moving this code, but PageLocked includes an implicit compound_head():
1. __PAGEFLAG(Locked, locked, PF_NO_TAIL)
2. #define __PAGEFLAG(uname, lname, policy) \ TESTPAGEFLAG(uname, lname, policy) \
3. #define TESTPAGEFLAG(uname, lname, policy) \ static __always_inline int Page##uname(struct page *page) \ { return test_bit(PG_##lname, &policy(page, 0)->flags); }
4. #define PF_NO_TAIL(page, enforce) ({ \ VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page); \ PF_POISONED_CHECK(compound_head(page)); })
5. #define PF_POISONED_CHECK(page) ({ \ VM_BUG_ON_PGFLAGS(PagePoisoned(page), page); \ page; })
This macrology isn't easy to understand the first time you read it (nor, indeed, the tenth time), so let me decode it:
Substitute 5 into 4 and remove irrelevancies:
6. #define PF_NO_TAIL(page, enforce) compound_head(page)
Expand 1 in 2:
7. TESTPAGEFLAG(Locked, locked, PF_NO_TAIL)
Expand 7 in 3:
8. static __always_inline int PageLocked(struct page *page) { return test_bit(PG_locked, &PF_NO_TAIL(page, 0)->flags); }
Expand 6 in 8:
9. static __always_inline int PageLocked(struct page *page) { return test_bit(PG_locked, &compound_head(page)->flags); }
(in case it's not clear, compound_head() is idempotent. that is: f(f(a)) == f(a))