On Tue, Dec 07, 2021 at 01:39:06PM -0800, Jaegeuk Kim wrote:
> On 12/07, Matthew Wilcox wrote:
> > > > Call Trace:
> > > > <TASK>
> > > > folio_mark_dirty+0x136/0x270 mm/page-writeback.c:2639
> >
> > if (likely(mapping)) {
> > ...
> > if (folio_test_reclaim(folio))
> > folio_clear_reclaim(folio);
> > return mapping->a_ops->set_page_dirty(&folio->page);
> >
> > how do we get to a NULL ->set_page_dirty for a metadata page's
> > mapping->a_ops? This is definitely an f2fs expert question.
>
> I can't find anything in f2fs, since that page was got by f2fs_grab_meta_page
> along with grab_cache_page() that we never unlocked it.
>
> 40 struct page *f2fs_grab_meta_page(struct f2fs_sb_info *sbi, pgoff_t index)
> 41 {
> 42 struct address_space *mapping = META_MAPPING(sbi);
> 43 struct page *page;
> 44 repeat:
> 45 page = f2fs_grab_cache_page(mapping, index, false);
>
> -> grab_cache_page(mapping, index);
>
> 46 if (!page) {
> 47 cond_resched();
> 48 goto repeat;
> 49 }
> 50 f2fs_wait_on_page_writeback(page, META, true, true);
> 51 if (!PageUptodate(page))
> 52 SetPageUptodate(page);
> 53 return page;
> 54 }
>
>
> Suspecting something in folio wrt folio_mapping()?
>
> 81 bool set_page_dirty(struct page *page)
> 82 {
> 83 return folio_mark_dirty(page_folio(page));
> 84 }
... huh? How could folio_mapping() be getting this wrong?
page_folio() does the same thing as compound_head() -- as far as I know
you don't use compound pages for f2fs metadata, so this basically just
casts the page to a struct folio.
folio_mapping() is just like the old page_mapping() (see commit
2f52578f9c64). Unless you've done something like set the swapcache
bit on your metadata page, it's just going to return folio->mapping
(ie the same as page->mapping).
