Messages in this thread | | | Date | Wed, 04 Mar 2015 13:09:51 +0100 | From | Vlastimil Babka <> | Subject | Re: [PATCHv3 04/24] rmap: add argument to charge compound page |
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On 03/04/2015 12:52 PM, Kirill A. Shutemov wrote: > On Mon, Feb 23, 2015 at 05:21:31PM +0100, Vlastimil Babka wrote: >> On 02/12/2015 05:18 PM, Kirill A. Shutemov wrote: >>> @@ -1052,21 +1052,24 @@ void page_add_anon_rmap(struct page *page, >>> * Everybody else should continue to use page_add_anon_rmap above. >>> */ >>> void do_page_add_anon_rmap(struct page *page, >>> - struct vm_area_struct *vma, unsigned long address, int exclusive) >>> + struct vm_area_struct *vma, unsigned long address, int flags) >>> { >>> int first = atomic_inc_and_test(&page->_mapcount); >>> if (first) { >>> + bool compound = flags & RMAP_COMPOUND; >>> + int nr = compound ? hpage_nr_pages(page) : 1; >> >> hpage_nr_pages(page) is: >> >> static inline int hpage_nr_pages(struct page *page) >> { >> if (unlikely(PageTransHuge(page))) >> return HPAGE_PMD_NR; >> return 1; >> } >> >> and later... >> >>> /* >>> * We use the irq-unsafe __{inc|mod}_zone_page_stat because >>> * these counters are not modified in interrupt context, and >>> * pte lock(a spinlock) is held, which implies preemption >>> * disabled. >>> */ >>> - if (PageTransHuge(page)) >>> + if (compound) { >>> + VM_BUG_ON_PAGE(!PageTransHuge(page), page); >> >> this means that we could assume that >> (compound == true) => (PageTransHuge(page) == true) >> >> and simplify above to: >> >> int nr = compound ? HPAGE_PMD_NR : 1; >> >> Right? > > No. HPAGE_PMD_NR is defined based on HPAGE_PMD_SHIFT which is BUILD_BUG() > without CONFIG_TRANSPARENT_HUGEPAGE. We will get compiler error without > the helper.
Oh, OK. But that doesn't mean there couldn't be another helper that would work in this case, or even open-coded #ifdefs in these functions. Apparently "compound" has to be always false for !CONFIG_TRANSPARENT_HUGEPAGE, as in that case PageTransHuge is defined as 0 and the VM_BUG_ON would trigger if compound was true. So without such ifdefs or wrappers, you are also adding dead code and pointless tests for !CONFIG_TRANSPARENT_HUGEPAGE?
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