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

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Message-ID: <Yrr/oBlf1Eig8uKS@casper.infradead.org>
Date:   Tue, 28 Jun 2022 14:18:24 +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 12:31:55PM +0100, Matthew Wilcox wrote:
> On Tue, Jun 28, 2022 at 12:27:40PM +0100, Matthew Wilcox wrote:
> > 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:
> 
> Argh, try one that actually compiles.

... that one's going to underflow the accounting.  Maybe I shouldn't
be writing code at 6am?

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f7248002dad9..4eec6ee83e44 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -18,6 +18,7 @@
 #include <linux/shrinker.h>
 #include <linux/mm_inline.h>
 #include <linux/swapops.h>
+#include <linux/backing-dev.h>
 #include <linux/dax.h>
 #include <linux/khugepaged.h>
 #include <linux/freezer.h>
@@ -2439,11 +2440,15 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 		__split_huge_page_tail(head, i, lruvec, list);
 		/* Some pages can be beyond EOF: drop them from page cache */
 		if (head[i].index >= end) {
-			ClearPageDirty(head + i);
-			__delete_from_page_cache(head + i, NULL);
+			struct folio *tail = page_folio(head + i);
+
 			if (shmem_mapping(head->mapping))
 				shmem_uncharge(head->mapping->host, 1);
-			put_page(head + i);
+			else if (folio_test_clear_dirty(tail))
+				folio_account_cleaned(tail,
+					inode_to_wb(folio->mapping->host));
+			__filemap_remove_folio(tail, NULL);
+			folio_put(tail);
 		} else if (!PageAnon(page)) {
 			__xa_store(&head->mapping->i_pages, head[i].index,
 					head + i, 0);