linux-kernel - Re: Multi-page folio issues in 5.19-rc4 (was [PATCH v3 25/25] xfs: Support large folios)

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Date:   Tue, 28 Jun 2022 12:27:40 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org
Subject: Re: Multi-page folio issues in 5.19-rc4 (was [PATCH v3 25/25] xfs:
 Support large folios)

On Tue, Jun 28, 2022 at 05:31:20PM +1000, Dave Chinner wrote:
> So using this technique, I've discovered that there's a dirty page
> accounting leak that eventually results in fsx hanging in
> balance_dirty_pages().

Alas, I think this is only an accounting error, and not related to
the problem(s) that Darrick & Zorro are seeing.  I think what you're
seeing is dirty pages being dropped at truncation without the
appropriate accounting.  ie this should be the fix:

+++ b/mm/huge_memory.c
@@ -2443,6 +2443,8 @@ static void __split_huge_page(struct page *page, struct list_head *list,
                        __delete_from_page_cache(head + i, NULL);
                        if (shmem_mapping(head->mapping))
                                shmem_uncharge(head->mapping->host, 1);
+                       else
+                               folio_account_cleaned(page_folio(head + i));
                        put_page(head + i);
                } else if (!PageAnon(page)) {
                        __xa_store(&head->mapping->i_pages, head[i].index,