linux-kernel - [patch for-4.12] mm, thp: remove cond_resched from __collapse_huge_page

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Date:   Mon, 19 Jun 2017 13:43:11 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Larry Finger <Larry.Finger@...inger.net>
cc:     Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: [patch for-4.12] mm, thp: remove cond_resched from
 __collapse_huge_page_copy

This is a partial revert of commit 338a16ba1549 ("mm, thp: copying user
pages must schedule on collapse") which added a cond_resched() to
__collapse_huge_page_copy().

On x86 with CONFIG_HIGHPTE, __collapse_huge_page_copy is called in atomic
context and thus scheduling is not possible.  This is only a possible
config on arm and i386.

Although need_resched has been shown to be set for over 100 jiffies while
doing the iteration in __collapse_huge_page_copy, this is better than
doing

	if (in_atomic())
		cond_resched()

to cover only non-CONFIG_HIGHPTE configs.

Reported-by: Larry Finger <Larry.Finger@...inger.net>
Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 Note: Larry should be back as of June 17 to test if this fixes the
 reported issue.

 mm/khugepaged.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -652,7 +652,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 			spin_unlock(ptl);
 			free_page_and_swap_cache(src_page);
 		}
-		cond_resched();
 	}
 }