linux-kernel - Re: [PATCH v4 2/3] thp: add HPAGE_PMD_* definitions for !CONFIG_TRANSPARENT

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Message-Id: <20120321154721.3b8884bd.akpm@linux-foundation.org>
Date:	Wed, 21 Mar 2012 15:47:21 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Hillf Danton <dhillf@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-next@...r.kernel.org
Subject: Re: [PATCH v4 2/3] thp: add HPAGE_PMD_* definitions for
 !CONFIG_TRANSPARENT_HUGEPAGE

On Wed, 21 Mar 2012 18:07:41 -0400
Paul Gortmaker <paul.gortmaker@...driver.com> wrote:

> On Mon, Mar 12, 2012 at 6:30 PM, Naoya Horiguchi
> <n-horiguchi@...jp.nec.com> wrote:
> > These macros will be used in later patch, where all usage are expected
> > to be optimized away without #ifdef CONFIG_TRANSPARENT_HUGEPAGE.
> > But to detect unexpected usages, we convert existing BUG() to BUILD_BUG().
> 
> Just a heads up that this showed up in linux-next today as the
> cause of a new build failure for an ARM board:
> 
> http://kisskb.ellerman.id.au/kisskb/buildresult/5930053/

The internet started working again.

mm/pgtable-generic.c: In function 'pmdp_clear_flush_young':
mm/pgtable-generic.c:76: error: call to '__build_bug_failed' declared with attribute error: BUILD_BUG failed

I guess we shouldn't be evaluating HPAGE_PMD_MASK at all if
!CONFIG_TRANSPARENT_HUGEPAGE, so...

--- a/mm/pgtable-generic.c~thp-add-hpage_pmd_-definitions-for-config_transparent_hugepage-fix
+++ a/mm/pgtable-generic.c
@@ -70,10 +70,11 @@ int pmdp_clear_flush_young(struct vm_are
 			   unsigned long address, pmd_t *pmdp)
 {
 	int young;
-#ifndef CONFIG_TRANSPARENT_HUGEPAGE
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
+#else
 	BUG();
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
-	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 	young = pmdp_test_and_clear_young(vma, address, pmdp);
 	if (young)
 		flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
_

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