From: Andrew Morton <akpm@linux-foundation.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [PATCH] mm: Make PageType more efficient
Date: Tue, 10 Mar 2020 18:10:27 -0700 [thread overview]
Message-ID: <20200310181027.232cff5b00600e1f056a4177@linux-foundation.org> (raw)
In-Reply-To: <20200310185609.5401-1-willy@infradead.org>
On Tue, 10 Mar 2020 11:56:09 -0700 Matthew Wilcox <willy@infradead.org> wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> PageType is a little hard for GCC to reason about, By checking
> ((~A) & flag) instead of (flag & (A | MASK) == MASK), GCC can do
> better optimisations, saving 652 bytes in page_alloc.o (which is
> a heavy user of PageBuddy).
>
> ...
>
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -725,14 +725,14 @@ PAGEFLAG_FALSE(DoubleMap)
> #define PG_table 0x00000400
> #define PG_guard 0x00000800
>
> -#define PageType(page, flag) \
> - ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
> -
> static inline int page_has_type(struct page *page)
> {
> return (int)page->page_type < PAGE_MAPCOUNT_RESERVE;
> }
>
> +#define PageType(page, flag) \
> + (page_has_type(page) && (~page->page_type & flag))
> +
`flag' should be parenthesized here. As should `page' if one is even
more paranoid.
I tried this:
--- a/include/linux/page-flags.h~mm-make-pagetype-more-efficient-fix
+++ a/include/linux/page-flags.h
@@ -731,7 +731,7 @@ static inline int page_has_type(struct p
}
#define PageType(page, flag) \
- (page_has_type(page) && (~page->page_type & flag))
+ (page_has_type(page) && !(page->page_type & ~(flag)))
#define PAGE_TYPE_OPS(uname, lname) \
static __always_inline int Page##uname(struct page *page) \
and page_alloc.o shrunk by 6782 bytes, half of it in
get_page_from_freelist(). Something crazy is going on. gcc-7.2.0.
next prev parent reply other threads:[~2020-03-11 1:10 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-10 18:56 [PATCH] mm: Make PageType more efficient Matthew Wilcox
2020-03-10 20:17 ` Alexander Duyck
2020-03-10 20:37 ` Matthew Wilcox
2020-03-10 21:50 ` Alexander Duyck
2020-03-11 13:13 ` Matthew Wilcox
2020-03-11 17:14 ` Ira Weiny
2020-03-11 17:22 ` Alexander Duyck
2020-03-11 1:10 ` Andrew Morton [this message]
2020-03-11 13:21 ` Matthew Wilcox
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