On Tue, 9 Feb 2021, Johannes Weiner wrote: > Page writeback doesn't hold a page reference, which allows truncate to > free a page the second PageWriteback is cleared. This used to require > special attention in test_clear_page_writeback(), where we had to be > careful not to rely on the unstable page->memcg binding and look up > all the necessary information before clearing the writeback flag. > > Since commit 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and > BUG_ON(PageWriteback)") test_clear_page_writeback() is called with an > explicit reference on the page, and this dance is no longer needed. > > Use unlock_page_memcg() and dec_lruvec_page_stat() directly.
s/stat()/state()/ This is a nice cleanup: I hadn't seen that connection at all. But I think you should take it further: __unlock_page_memcg() can then be static in mm/memcontrol.c, and its declarations deleted from include/linux/memcontrol.h? And further: delete __dec_lruvec_state() and dec_lruvec_state() from include/linux/vmstat.h - unless you feel that every "inc" ought to be matched by a "dec", even when unused. > > Signed-off-by: Johannes Weiner <han...@cmpxchg.org> Acked-by: Hugh Dickins <hu...@google.com> > --- > mm/page-writeback.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index eb34d204d4ee..f6c2c3165d4d 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -2722,12 +2722,9 @@ EXPORT_SYMBOL(clear_page_dirty_for_io); > int test_clear_page_writeback(struct page *page) > { > struct address_space *mapping = page_mapping(page); > - struct mem_cgroup *memcg; > - struct lruvec *lruvec; > int ret; > > - memcg = lock_page_memcg(page); > - lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page)); > + lock_page_memcg(page); > if (mapping && mapping_use_writeback_tags(mapping)) { > struct inode *inode = mapping->host; > struct backing_dev_info *bdi = inode_to_bdi(inode); > @@ -2755,11 +2752,11 @@ int test_clear_page_writeback(struct page *page) > ret = TestClearPageWriteback(page); > } > if (ret) { > - dec_lruvec_state(lruvec, NR_WRITEBACK); > + dec_lruvec_page_state(page, NR_WRITEBACK); > dec_zone_page_state(page, NR_ZONE_WRITE_PENDING); > inc_node_page_state(page, NR_WRITTEN); > } > - __unlock_page_memcg(memcg); > + unlock_page_memcg(page); > return ret; > } > > -- > 2.30.0