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mm: store compound_nr as well as compound_order
Patch series "THP prep patches". These are some generic cleanups and improvements, which I would like merged into mmotm soon. The first one should be a performance improvement for all users of compound pages, and the others are aimed at getting code to compile away when CONFIG_TRANSPARENT_HUGEPAGE is disabled (ie small systems). Also better documented / less confusing than the current prefix mixture of compound, hpage and thp. This patch (of 7): This removes a few instructions from functions which need to know how many pages are in a compound page. The storage used is either page->mapping on 64-bit or page->index on 32-bit. Both of these are fine to overlay on tail pages. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: William Kucharski <william.kucharski@oracle.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Cc: David Hildenbrand <david@redhat.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Link: http://lkml.kernel.org/r/20200629151959.15779-1-willy@infradead.org Link: http://lkml.kernel.org/r/20200629151959.15779-2-willy@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -922,12 +922,15 @@ static inline int compound_pincount(struct page *page)
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static inline void set_compound_order(struct page *page, unsigned int order)
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{
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page[1].compound_order = order;
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page[1].compound_nr = 1U << order;
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}
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/* Returns the number of pages in this potentially compound page. */
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static inline unsigned long compound_nr(struct page *page)
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{
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return 1UL << compound_order(page);
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if (!PageHead(page))
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return 1;
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return page[1].compound_nr;
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}
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/* Returns the number of bytes in this potentially compound page. */
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@ -134,6 +134,7 @@ struct page {
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unsigned char compound_dtor;
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unsigned char compound_order;
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atomic_t compound_mapcount;
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unsigned int compound_nr; /* 1 << compound_order */
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};
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struct { /* Second tail page of compound page */
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unsigned long _compound_pad_1; /* compound_head */
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@ -666,8 +666,6 @@ void prep_compound_page(struct page *page, unsigned int order)
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int i;
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int nr_pages = 1 << order;
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set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
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set_compound_order(page, order);
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__SetPageHead(page);
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for (i = 1; i < nr_pages; i++) {
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struct page *p = page + i;
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@ -675,6 +673,9 @@ void prep_compound_page(struct page *page, unsigned int order)
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p->mapping = TAIL_MAPPING;
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set_compound_head(p, page);
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}
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set_compound_page_dtor(page, COMPOUND_PAGE_DTOR);
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set_compound_order(page, order);
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atomic_set(compound_mapcount_ptr(page), -1);
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if (hpage_pincount_available(page))
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atomic_set(compound_pincount_ptr(page), 0);
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