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Date: Wed, 6 Mar 2019 11:26:49 +0100 From: Arnd Bergmann <arnd@...db.de> To: Anshuman Khandual <anshuman.khandual@....com> Cc: Jérôme Glisse <jglisse@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Ralph Campbell <rcampbell@...dia.com>, Stephen Rothwell <sfr@...b.auug.org.au>, John Hubbard <jhubbard@...dia.com>, Dan Williams <dan.j.williams@...el.com>, Linux-MM <linux-mm@...ck.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] mm/hmm: fix unused variable warnings On Tue, Mar 5, 2019 at 1:18 PM Anshuman Khandual <anshuman.khandual@....com> wrote: > On 03/05/2019 01:30 AM, Arnd Bergmann wrote: > > When CONFIG_HUGETLB_PAGE is disabled, the only use of the variable 'h' > > is compiled out, and the compiler thinks it is unnecessary: > > > > mm/hmm.c: In function 'hmm_range_snapshot': > > mm/hmm.c:1015:19: error: unused variable 'h' [-Werror=unused-variable] > > struct hstate *h = hstate_vma(vma); > > After doing some Kconfig hacks like (ARCH_WANT_GENERAL_HUGETLB = n) on an > X86 system I got (HUGETLB_PAGE = n and HMM = y) config. But was unable to > hit the build error. Helper is_vm_hugetlb_page() seems to always return > false when HUGETLB_PAGE = n. Would not the compiler remove the entire code > block including the declaration for 'h' ? > > #ifdef CONFIG_HUGETLB_PAGE > #include <linux/mm.h> > static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma) > { > return !!(vma->vm_flags & VM_HUGETLB); > } > #else > static inline bool is_vm_hugetlb_page(struct vm_area_struct *vma) > { > return false; > } > #endif The is_vm_hugetlb_page() check is unrelated to the warning here, the problem is that huge_page_shift() is defined as #define huge_page_shift(h) PAGE_SHIFT when CONFIG_HUGETLB_PAGE is disabled, so after preprocessing, the only reference to the variable is removed. Arnd
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