linux-kernel - Re: [PATCHi v2] mm: put_and_wait_on_page

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Message-ID: <CAHk-=wisu7SHwHYo6TKo6t5CM6Da66jGsMgXKdrfNa-fDzdP5g@mail.gmail.com>
Date:   Tue, 27 Nov 2018 08:58:30 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Lameter <cl@...ux.com>
Cc:     rppt@...ux.ibm.com, Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, bhe@...hat.com,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>, david@...hat.com,
        mgorman@...hsingularity.net,
        David Herrmann <dh.herrmann@...il.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, kan.liang@...el.com,
        Andi Kleen <ak@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Piggin <npiggin@...il.com>, pifang@...hat.com,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [PATCHi v2] mm: put_and_wait_on_page_locked() while page is migrated

On Tue, Nov 27, 2018 at 8:49 AM Christopher Lameter <cl@...ux.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