On Wed, Feb 24, 2021 at 05:15:58AM -0800, Andrew Morton wrote: > Here's what the preprocessor produces for an allmodconfig version of > PageActive(): > > static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((no_instrument_function)) __attribute__((__always_inline__)) int PageActive(struct page *page) > { > return test_bit(PG_active, &({ do { if (__builtin_expect(!!(PagePoisoned(compound_head(page))), 0)) { dump_page(compound_head(page), "VM_BUG_ON_PAGE(" "PagePoisoned(compound_head(page))"")"); do { ({ asm volatile("%c0: nop\n\t" ".pushsection .discard.instr_begin\n\t" ".long %c0b - .\n\t" ".popsection\n\t" : : "i" (373)); }); do { asm volatile("1:\t" ".byte 0x0f, 0x0b" "\n" ".pushsection __bug_table,\"aw\"\n" "2:\t" ".long " "1b" " - 2b" "\t# bug_entry::bug_addr\n" "\t" ".long " "%c0" " - 2b" "\t# bug_entry::file\n" "\t.word %c1" "\t# bug_entry::line\n" "\t.word %c2" "\t# bug_entry::flags\n" "\t.org 2b+%c3\n" ".popsection" : : "i" ("./include/linux/page-flags.h"), "i" (338), "i" (0), "i" (sizeof(struct bug_entry))); } while (0); do { ({ asm volatile("%c0:\n\t" ".pushsection .discard.unreachable\n\t" ".long %c0b - .\n\t" ".popsection\n\t" : : "i" (374)); }); asm volatile(""); __builtin_unreachable(); } while (0); } while (0); } } while (0); compound_head(page); })->flags); > > } > > That's all to test a single bit! > > Four calls to compound_head(). If only somebody were working on a patch series to get rid of all those calls to compound_head()! Some reviews on https://lore.kernel.org/linux-mm/20210128070404.1922318-2-willy@xxxxxxxxxxxxx/ would be nice. So, I haven't done page_lru() yet in my folio tree. What I would do is: diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 355ea1ee32bd..3895cfe6502b 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -63,22 +63,27 @@ static __always_inline void __clear_page_lru_flags(struct page *page) * Returns the LRU list a page should be on, as an index * into the array of LRU lists. */ -static __always_inline enum lru_list page_lru(struct page *page) +static __always_inline enum lru_list folio_lru(struct folio *folio) { enum lru_list lru; - VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page); + VM_BUG_ON_PAGE(FolioActive(folio) && FolioUnevictable(folio), folio); - if (PageUnevictable(page)) + if (FolioUnevictable(folio)) return LRU_UNEVICTABLE; - lru = page_is_file_lru(page) ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON; - if (PageActive(page)) + lru = page_is_file_lru(&folio->page) ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON; + if (FolioActive(folio)) lru += LRU_ACTIVE; return lru; } +static __always_inline enum lru_list page_lru(struct page *page) +{ + return folio_lru(page_folio(page)); +} + static __always_inline void add_page_to_lru_list(struct page *page, struct lruvec *lruvec) { That would cause compound_head() to be called once instead of four times (assuming VM_BUG_ON is enabled). It can be reduced down to zero times when the callers are converted from being page-based to being folio-based. There is a further problem with PageFoo() being a READ_ONCE() of page->flags, so the compiler can't CSE it. I have ideas in that direction too; essentially ... unsigned long page_flags = PageFlags(page); if (PageFlagUnevictable(flags)) ... if (PageFlagsActive(flags)) ... and we can generate the PageFlagsFoo macros with the same machinery in page-flags.h that generates PageFoo and FolioFoo. This strikes me as less critical than the folio work to remove all the unnecessary calls to compound_head(). > movq %rbx, %rbp # page, _14 > # ./include/linux/page-flags.h:184: unsigned long head = READ_ONCE(page->compound_head); > call __sanitizer_cov_trace_pc # It's a bit unfair to complain about code generation with a sanitizer-enabled build ...