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Subject: Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for
 our internal use
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org
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From:   Chao Yu <chao@kernel.org>
Message-ID: <fc0de0c2-a3b6-df91-5b90-524768a85d82@kernel.org>
Date:   Sat, 10 Jul 2021 16:11:38 +0800
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On 2021/7/7 17:57, Mel Gorman wrote:
> I think it would work but it would be preferable to find out why the
> tail page has an order set in the first place. I've looked over

Agreed.

> mm/page_alloc.c and mm/compaction.c a few times and did not spot where
> set_private_page(page, 0) is missed when it should be covered by
> clear_page_guard or del_page_from_free_list :(

I didn't enable CONFIG_DEBUG_PAGEALLOC, so we will expect page private
should be cleared by del_page_from_free_list(), but I guess it only clears
the buddy's private field rather than original page's, so I added below
diff and check the dmesg, it looks stall private value in original page
will be left commonly... Let me know if I missed something?

---
  mm/page_alloc.c | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a06bcfe6f786..1e7031ff548e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1029,6 +1029,7 @@ static inline void __free_one_page(struct page *page,
  	unsigned long combined_pfn;
  	unsigned int max_order;
  	struct page *buddy;
+	struct page *orig_page = page;
  	bool to_tail;

  	max_order = min_t(unsigned int, MAX_ORDER - 1, pageblock_order);
@@ -1097,6 +1098,10 @@ static inline void __free_one_page(struct page *page,

  done_merging:
  	set_buddy_order(page, order);
+	if (orig_page != page) {
+		if (WARN_ON_ONCE(orig_page->private))
+			pr_info("2order:%x, origpage.private:%x", order, orig_page->private);
+	}

  	if (fpi_flags & FPI_TO_TAIL)
  		to_tail = true;
-- 
2.22.1


>