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From: Zhan Chen <zhanc1@andrew.cmu.edu>
Date: Tue, 19 Jul 2016 15:53:16 -0700
Message-ID: <CAAs6xrzboZpT9o+u+xwnjVJHn_bip2jkZAg7gbQRVmv6VhAxxA@mail.gmail.com>
Subject: migration failure in 3.10 kernel
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To: n-horiguchi@ah.jp.nec.com
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Hi Naoya,

I encounter the issue that page migration fails due to page ref count != 1
thus return -EAGAIN in migrate_page_move_mapping().
And it turns out that in page fault handling, __migration_entry_wait()
calls get_page_unless_zero() to get an extra ref count before
wait_on_page_locked().

Is there a fix that can safely wait for migration to complete without
taking the ref on page?
Thanks.

-Zhan

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<div dir=3D"ltr">Hi Naoya,<div><br><div>I encounter the issue that page mig=
ration fails due to page ref count !=3D 1 thus return -EAGAIN in=C2=A0migra=
te_page_move_mapping().</div><div>And it turns out that in page fault handl=
ing,=C2=A0__migration_entry_wait() calls=C2=A0get_page_unless_zero() to get=
 an extra ref count before wait_on_page_locked().</div><div><br></div><div>=
Is there a fix that can safely wait for migration to complete without takin=
g the ref on page?</div><div>Thanks.</div><div><br></div><div>-Zhan</div></=
div></div>

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