From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Yu Zhao <yuzhao@google.com>,
vbabka@suse.cz, alex.shi@linux.alibaba.com, guro@fb.com,
hannes@cmpxchg.org, hughd@google.com,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
mhocko@kernel.org, vdavydov.dev@gmail.com
Subject: Re: [PATCH] mm: test page->flags directly in page_lru()
Date: Wed, 24 Feb 2021 21:56:39 +0000 [thread overview]
Message-ID: <20210224215639.GT2858050@casper.infradead.org> (raw)
In-Reply-To: <20210224051558.79e31c60eea2c088f4a1b300@linux-foundation.org>
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@infradead.org/
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 ...
next prev parent reply other threads:[~2021-02-24 21:57 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-22 22:05 [PATCH v2 00/10] mm: lru related cleanups Yu Zhao
2021-01-22 22:05 ` [PATCH v2 01/10] mm: use add_page_to_lru_list() Yu Zhao
2021-01-26 18:57 ` Vlastimil Babka
2021-01-27 2:12 ` Miaohe Lin
2021-01-22 22:05 ` [PATCH v2 02/10] mm: shuffle lru list addition and deletion functions Yu Zhao
2021-01-26 18:58 ` Vlastimil Babka
2021-01-27 2:14 ` Miaohe Lin
2021-01-22 22:05 ` [PATCH v2 03/10] mm: don't pass "enum lru_list" to lru list addition functions Yu Zhao
2021-01-26 19:13 ` Vlastimil Babka
2021-01-26 21:34 ` Yu Zhao
2021-01-27 10:51 ` Vlastimil Babka
2021-01-26 22:01 ` Matthew Wilcox
2021-01-26 22:14 ` Yu Zhao
2021-02-23 22:50 ` Andrew Morton
2021-02-24 5:29 ` Yu Zhao
2021-02-24 8:06 ` Alex Shi
2021-02-24 8:37 ` Yu Zhao
2021-02-24 9:01 ` Alex Shi
2021-01-22 22:05 ` [PATCH v2 04/10] mm: don't pass "enum lru_list" to trace_mm_lru_insertion() Yu Zhao
2021-01-22 22:05 ` [PATCH v2 05/10] mm: don't pass "enum lru_list" to del_page_from_lru_list() Yu Zhao
2021-01-22 22:05 ` [PATCH v2 06/10] mm: add __clear_page_lru_flags() to replace page_off_lru() Yu Zhao
2021-01-22 22:05 ` [PATCH v2 07/10] mm: VM_BUG_ON lru page flags Yu Zhao
2021-01-22 22:05 ` [PATCH v2 08/10] mm: fold page_lru_base_type() into its sole caller Yu Zhao
2021-01-22 22:05 ` [PATCH v2 09/10] mm: fold __update_lru_size() " Yu Zhao
2021-01-22 22:06 ` [PATCH v2 10/10] mm: make lruvec_lru_size() static Yu Zhao
2021-02-24 8:48 ` [PATCH] mm: test page->flags directly in page_lru() Yu Zhao
2021-02-24 13:15 ` Andrew Morton
2021-02-24 19:57 ` Yu Zhao
2021-02-24 21:56 ` Matthew Wilcox [this message]
2021-02-24 22:34 ` Yu Zhao
2021-02-24 22:48 ` Matthew Wilcox
2021-02-24 23:50 ` Yu Zhao
2021-02-25 3:55 ` Matthew Wilcox
2021-02-25 5:22 ` Yu Zhao
2021-02-25 12:12 ` Matthew Wilcox
2021-02-26 9:17 ` [PATCH v2 0/3] trim the uses of compound_head() Yu Zhao
2021-02-26 9:17 ` [PATCH v2 1/3] mm: bypass compound_head() for PF_NO_TAIL when enforce=1 Yu Zhao
2021-02-26 9:17 ` [PATCH v2 2/3] mm: use PF_NO_TAIL for PG_lru Yu Zhao
2021-02-26 20:22 ` Yu Zhao
2021-02-26 9:17 ` [PATCH v2 3/3] mm: use PF_ONLY_HEAD for PG_active and PG_unevictable Yu Zhao
2021-02-26 12:13 ` Matthew Wilcox
2021-02-26 19:49 ` Yu Zhao
2021-02-26 20:27 ` Matthew Wilcox
2021-03-01 11:50 ` Kirill A. Shutemov
2021-03-01 19:58 ` Yu Zhao
2021-03-01 20:16 ` Hugh Dickins
2021-03-01 20:26 ` Matthew Wilcox
2021-02-26 10:52 ` [PATCH v2 0/3] trim the uses of compound_head() Vlastimil Babka
2021-02-26 19:04 ` Yu Zhao
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