linux-kernel - Re: [Question Resend] About z3fold page migration

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Date:   Mon, 12 Oct 2020 15:04:41 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Question Resend] About z3fold page migration

On Mon, Oct 12, 2020 at 02:00:17PM +0000, linmiaohe wrote:
> Hi all:
> 
> 	Many thanks for brilliant z3fold code. I am reading it and have some questions about it. It's very nice of you if you can explain it for me.
> 	1.page->private is used in z3fold but PagePrivate flag is never set, should we SetPagePrivate for it?

No.  SetPagePrivate and page->private are related in interesting and
complicated ways.  I'm working on some documentation for it at the moment,
but the short answer is: no.

> 	2.Since PagePrivate flag is never set, why we ClearPagePrivate in free_z3fold_page and z3fold_page_migrate?

That's probably a bug.

> 	3.Should we add page to the unbuddied list in z3fold_page_putback() when zhdr->refcount does not reach 0 since we remove it from unbuddied list
> in z3fold_page_isolate? Or When we will add page to the unbuddied list after z3fold_page_putback?

This one I do not know the answer to.