Am 17.06.2016 um 20:27 schrieb Michal Hocko:
> On Fri 17-06-16 18:55:45, Richard Weinberger wrote:
>> Am 17.06.2016 um 18:28 schrieb Michal Hocko:
>>> But doesn't this disable the page migration and so potentially reduce
>>> the compaction success rate for the large pile of filesystems? Without
>>> any hint about that?
>>
>> The WARN_ON_ONCE() is the hint. ;)
>
> Right. My reply turned a different way than I meant... I meant to say
> that there might be different regressions caused by this change without much
> hint that a particular warning would be the smoking gun...
>
Okay, what about something like that?
That way everything works as before and we don't have regressions
but FS maintainers will notice the WARN_ON_ONCE() and hopefully review
whether generic_migrate_page() is really suitable.
If so, they can set their a_ops->migratepage to generic_migrate_page().
@@ -771,8 +773,15 @@ static int move_to_new_page(struct page *newpage, struct page *page,
* is the most common path for page migration.
*/
rc = mapping->a_ops->migratepage(mapping, newpage, page, mode);
- else
- rc = fallback_migrate_page(mapping, newpage, page, mode);
+ else {
+ /*
+ * Dear filesystem maintainer, please verify whether
+ * generic_migrate_page() is suitable for your
+ * filesystem, especially wrt. page flag handling.
+ */
+ WARN_ON_ONCE(1);
+ rc = generic_migrate_page(mapping, newpage, page, mode);
+ }
/*
* When successful, old pagecache page->mapping must be cleared before
Thanks,
//richard
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