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SubjectRe: [PATCH v2] mm,thp: recheck each page before collapsing file THP
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> On Oct 18, 2019, at 9:58 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
>
> 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 THP
>>> and file THP.
>>>
>>> Current khugepaged should not try to collapse dirty file THP, because it
>>> is limited to read only text. Add a PageDirty check and warning for file
>>> THP. This is added after page_mapping() check, because if the page is
>>> truncated, it might be dirty.
>>>
>>> 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>
>>
>> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>
> We should also be able to remove the unlocked tests for those two
> conditions, right?

Yeah, I think we can remove them.

Thanks,
Song

>
> 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 = SCAN_FAIL;
> goto xa_unlocked;
> }
> - } else if (!PageUptodate(page)) {
> - xas_unlock_irq(&xas);
> - wait_on_page_locked(page);
> - if (!trylock_page(page)) {
> - result = SCAN_PAGE_LOCK;
> - goto xa_unlocked;
> - }
> - get_page(page);
> - } else if (PageDirty(page)) {
> - result = SCAN_FAIL;
> - goto xa_locked;
> } else if (trylock_page(page)) {
> get_page(page);
> xas_unlock_irq(&xas);

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