linux-kernel - Re: [PATCH v2 1/5] mm/migrate.c: remove unnecessary VM_BUG_ON_PAGE on putback_movable

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Message-ID: <CAHbLzkrde4fMZtt7g+5HJ8PftwwDBvg-8b=W4F_64_EK-CusUA@mail.gmail.com>
Date:   Tue, 23 Mar 2021 10:58:45 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Rafael Aquini <aquini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Alistair Popple <apopple@...dia.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/5] mm/migrate.c: remove unnecessary VM_BUG_ON_PAGE on putback_movable_page()

On Tue, Mar 23, 2021 at 6:54 AM Miaohe Lin <linmiaohe@...wei.com> wrote:
>
> The !PageLocked() check is implicitly done in PageMovable(). Remove this
> explicit one.

TBH, I'm a little bit reluctant to have this kind change. If "locked"
check is necessary we'd better make it explicit otherwise just remove
it.

And why not just remove all the 3 VM_BUG_ON_PAGE since
putback_movable_page() is just called by putback_movable_pages() and
we know the page is locked and both PageMovable and PageIsolated is
checked right before calling putback_movable_page().

And you also could make putback_movable_page() static.

> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/migrate.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 47df0df8f21a..facec65c7374 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -145,7 +145,6 @@ void putback_movable_page(struct page *page)
>  {
>         struct address_space *mapping;
>
> -       VM_BUG_ON_PAGE(!PageLocked(page), page);
>         VM_BUG_ON_PAGE(!PageMovable(page), page);
>         VM_BUG_ON_PAGE(!PageIsolated(page), page);
>
> --
> 2.19.1
>