linux-kernel - Re: [PATCH] numa: fix /proc/<pid>/numa

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Message-Id: <20160120122631.e9c8a842d36d6dba4bb25964@linux-foundation.org>
Date:	Wed, 20 Jan 2016 12:26:31 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	kbuild test robot <lkp@...el.com>
Cc:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>, kbuild-all@...org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	linux-mm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] numa: fix /proc/<pid>/numa_maps on s390

On Thu, 21 Jan 2016 03:32:41 +0800 kbuild test robot <lkp@...el.com> wrote:

> Hi Michael,
> 
> [auto build test ERROR on next-20160120]
> [cannot apply to v4.4-rc8 v4.4-rc7 v4.4-rc6 v4.4]
> [if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Michael-Holzheu/numa-fix-proc-pid-numa_maps-on-s390/20160121-022313
> config: ia64-alldefconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=ia64 
> 
> All errors (new ones prefixed by >>):
> 
>    fs/proc/task_mmu.c: In function 'gather_pte_stats':
> >> fs/proc/task_mmu.c:1523:3: error: implicit declaration of function 'huge_ptep_get' [-Werror=implicit-function-declaration]
>       pte_t huge_pte = huge_ptep_get((pte_t *)pmd);
>       ^

hm.

That whole code block in gather_pte_stats() just shouldn't exist when
CONFIG_TRANSPARENT_HUGEPAGE=n.  And because pmd_trans_huge_lock()
returns NULL, the compiler will nuke it all anyway.

So instead of doing the obvious:

--- a/fs/proc/task_mmu.c~numa-fix-proc-pid-numa_maps-on-s390-fix
+++ a/fs/proc/task_mmu.c
@@ -1524,7 +1524,11 @@ static int gather_pte_stats(pmd_t *pmd,
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
+#ifdef CONFIG_HUGETLB_PAGE
 		pte_t huge_pte = huge_ptep_get((pte_t *)pmd);
+#else
+		pte_t huge_pte = *(pte_t *)pmd;
+#endif
 		struct page *page;
 
 		page = can_gather_numa_stats(huge_pte, vma, addr);

I'm thinking we should do

--- a/fs/proc/task_mmu.c~numa-fix-proc-pid-numa_maps-on-s390-fix
+++ a/fs/proc/task_mmu.c
@@ -1523,6 +1523,7 @@ static int gather_pte_stats(pmd_t *pmd,
 	pte_t *pte;
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (ptl) {
 		pte_t huge_pte = huge_ptep_get((pte_t *)pmd);
 		struct page *page;
@@ -1534,6 +1535,7 @@ static int gather_pte_stats(pmd_t *pmd,
 		spin_unlock(ptl);
 		return 0;
 	}
+#endif
 
 	if (pmd_trans_unstable(pmd))
 		return 0;
_