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From:   Song Liu <songliubraving@fb.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
CC:     open list <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
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        "william.kucharski@oracle.com" <william.kucharski@oracle.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "Hugh Dickins" <hughd@google.com>
Subject: Re: [PATCH v2] mm,thp: recheck each page before collapsing file THP
Thread-Topic: [PATCH v2] mm,thp: recheck each page before collapsing file THP
Thread-Index: AQHVhdJpENZJXtqpok2fOupB1uQ0i6dgnG+AgAAChQCAAAf0AA==
Date:   Fri, 18 Oct 2019 17:27:12 +0000
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 <20191018164943.GA179426@cmpxchg.org> <20191018165844.GB179426@cmpxchg.org>
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> On Oct 18, 2019, at 9:58 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
>=20
> On Fri, Oct 18, 2019 at 12:49:46PM -0400, Johannes Weiner wrote:
>> On Fri, Oct 18, 2019 at 09:37:54AM -0700, Song Liu wrote:
>>> In collapse_file(), after locking the page, it is necessary to recheck
>>> that the page is up-to-date. Add PageUptodate() check for both shmem TH=
P
>>> and file THP.
>>>=20
>>> Current khugepaged should not try to collapse dirty file THP, because i=
t
>>> is limited to read only text. Add a PageDirty check and warning for fil=
e
>>> THP. This is added after page_mapping() check, because if the page is
>>> truncated, it might be dirty.
>>>=20
>>> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem)=
 FS")
>>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>> Cc: Hugh Dickins <hughd@google.com>
>>> Cc: William Kucharski <william.kucharski@oracle.com>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Signed-off-by: Song Liu <songliubraving@fb.com>
>>=20
>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>=20
> We should also be able to remove the unlocked tests for those two
> conditions, right?

Yeah, I think we can remove them.=20

Thanks,
Song

>=20
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 0a1b4b484ac5..a3ef6ce86bfa 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1601,17 +1601,6 @@ static void collapse_file(struct mm_struct *mm,
> 					result =3D SCAN_FAIL;
> 					goto xa_unlocked;
> 				}
> -			} else if (!PageUptodate(page)) {
> -				xas_unlock_irq(&xas);
> -				wait_on_page_locked(page);
> -				if (!trylock_page(page)) {
> -					result =3D SCAN_PAGE_LOCK;
> -					goto xa_unlocked;
> -				}
> -				get_page(page);
> -			} else if (PageDirty(page)) {
> -				result =3D SCAN_FAIL;
> -				goto xa_locked;
> 			} else if (trylock_page(page)) {
> 				get_page(page);
> 				xas_unlock_irq(&xas);