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SubjectRe: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem) FS
On Mon, Jun 24, 2019 at 02:42:13PM +0000, Song Liu wrote:
>
>
> > On Jun 24, 2019, at 7:27 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> >
> > On Mon, Jun 24, 2019 at 02:01:05PM +0000, Song Liu wrote:
> >>>> @@ -1392,6 +1403,23 @@ static void collapse_file(struct mm_struct *mm,
> >>>> result = SCAN_FAIL;
> >>>> goto xa_unlocked;
> >>>> }
> >>>> + } else if (!page || xa_is_value(page)) {
> >>>> + xas_unlock_irq(&xas);
> >>>> + page_cache_sync_readahead(mapping, &file->f_ra, file,
> >>>> + index, PAGE_SIZE);
> >>>> + lru_add_drain();
> >>>
> >>> Why?
> >>
> >> isolate_lru_page() is likely to fail if we don't drain the pagevecs.
> >
> > Please add a comment.
>
> Will do.
>
> >
> >>>> + page = find_lock_page(mapping, index);
> >>>> + if (unlikely(page == NULL)) {
> >>>> + result = SCAN_FAIL;
> >>>> + goto xa_unlocked;
> >>>> + }
> >>>> + } else if (!PageUptodate(page)) {
> >>>
> >>> Maybe we should try wait_on_page_locked() here before give up?
> >>
> >> Are you referring to the "if (!PageUptodate(page))" case?
> >
> > Yes.
>
> I think this case happens when another thread is reading the page in.
> I could not think of a way to trigger this condition for testing.
>
> On the other hand, with current logic, we will retry the page on the
> next scan, so I guess this is OK.

What I meant that calling wait_on_page_locked() on !PageUptodate() page
will likely make it up-to-date and we don't need to SCAN_FAIL the attempt.

--
Kirill A. Shutemov

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