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SubjectRe: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem) FS
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> 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.

Thanks,
Song
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