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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 27 Nov 2018 08:58:30 -0800
Message-ID: <CAHk-=wisu7SHwHYo6TKo6t5CM6Da66jGsMgXKdrfNa-fDzdP5g@mail.gmail.com>
Subject: Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is migrated
To:     Christoph Lameter <cl@linux.com>
Cc:     rppt@linux.ibm.com, Matthew Wilcox <willy@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, bhe@redhat.com,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Andrea Arcangeli <aarcange@redhat.com>, david@redhat.com,
        mgorman@techsingularity.net,
        David Herrmann <dh.herrmann@gmail.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, kan.liang@intel.com,
        Andi Kleen <ak@linux.intel.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Nick Piggin <npiggin@gmail.com>, pifang@redhat.com,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org
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On Tue, Nov 27, 2018 at 8:49 AM Christopher Lameter <cl@linux.com> wrote:
>
> A process has no refcount on a page struct and is waiting for it to become
> unlocked? Why? Should it not simply ignore that page and continue?

The problem isn't that you can just "continue".

You need to *retry*.

And you can't just busy-loop. You want to wait until the page state
has changed, and _then_ retry.

                  Linus