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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
To: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	akpm@linux-foundation.org
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Christoph Hellwig <hch@lst.de>,
	David Hildenbrand <david@redhat.com>, Zi Yan <ziy@nvidia.com>
Subject: [PATCH 1/8] mm: Optimise nth_page for contiguous memmap
Date: Fri, 30 Apr 2021 15:55:42 +0100	[thread overview]
Message-ID: <20210430145549.2662354-2-willy@infradead.org> (raw)
In-Reply-To: <20210430145549.2662354-1-willy@infradead.org>

If the memmap is virtually contiguous (either because we're using
a virtually mapped memmap or because we don't support a discontig
memmap at all), then we can implement nth_page() by simple addition.
Contrary to popular belief, the compiler is not able to optimise this
itself for a vmemmap configuration.  This reduces one example user (sg.c)
by four instructions:

        struct page *page = nth_page(rsv_schp->pages[k], offset >> PAGE_SHIFT);

before:
   49 8b 45 70             mov    0x70(%r13),%rax
   48 63 c9                movslq %ecx,%rcx
   48 c1 eb 0c             shr    $0xc,%rbx
   48 8b 04 c8             mov    (%rax,%rcx,8),%rax
   48 2b 05 00 00 00 00    sub    0x0(%rip),%rax
           R_X86_64_PC32      vmemmap_base-0x4
   48 c1 f8 06             sar    $0x6,%rax
   48 01 d8                add    %rbx,%rax
   48 c1 e0 06             shl    $0x6,%rax
   48 03 05 00 00 00 00    add    0x0(%rip),%rax
           R_X86_64_PC32      vmemmap_base-0x4

after:
   49 8b 45 70             mov    0x70(%r13),%rax
   48 63 c9                movslq %ecx,%rcx
   48 c1 eb 0c             shr    $0xc,%rbx
   48 c1 e3 06             shl    $0x6,%rbx
   48 03 1c c8             add    (%rax,%rcx,8),%rbx

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/mm.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 25b9041f9925..2327f99b121f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -234,7 +234,11 @@ int overcommit_policy_handler(struct ctl_table *, int, void *, size_t *,
 int __add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 		pgoff_t index, gfp_t gfp, void **shadowp);
 
+#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
 #define nth_page(page,n) pfn_to_page(page_to_pfn((page)) + (n))
+#else
+#define nth_page(page,n) ((page) + (n))
+#endif
 
 /* to align the pointer to the (next) page boundary */
 #define PAGE_ALIGN(addr) ALIGN(addr, PAGE_SIZE)
-- 
2.30.2


  reply	other threads:[~2021-04-30 14:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-30 14:55 [PATCH 0/8] Folio Prequel patches Matthew Wilcox (Oracle)
2021-04-30 14:55 ` Matthew Wilcox (Oracle) [this message]
2021-04-30 14:55 ` [PATCH 2/8] mm: Make __dump_page static Matthew Wilcox (Oracle)
2021-04-30 14:55 ` [PATCH 3/8] mm/debug: Factor PagePoisoned out of __dump_page Matthew Wilcox (Oracle)
2021-05-12  3:29   ` Kefeng Wang
2021-05-12  3:38     ` Matthew Wilcox
2021-05-12  3:53       ` Kefeng Wang
2021-04-30 14:55 ` [PATCH 4/8] mm/page_owner: Constify dump_page_owner Matthew Wilcox (Oracle)
2021-04-30 14:55 ` [PATCH 5/8] mm: Make compound_head const-preserving Matthew Wilcox (Oracle)
2021-04-30 14:55 ` [PATCH 6/8] mm: Constify get_pfnblock_flags_mask and get_pfnblock_migratetype Matthew Wilcox (Oracle)
2021-04-30 14:55 ` [PATCH 7/8] mm: Constify page_count and page_ref_count Matthew Wilcox (Oracle)
2021-04-30 14:55 ` [PATCH 8/8] mm: Fix struct page layout on 32-bit systems Matthew Wilcox (Oracle)
2021-05-10 16:12 ` [PATCH 0/8] Folio Prequel patches Matteo Croce
2021-05-10 16:29   ` Matthew Wilcox

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