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Subject[PATCH] mm: page-writeback: simplify memcg handling in test_clear_page_writeback()
Date
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.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
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
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