From: Christoph Hellwig <hch@lst.de>
To: linux-xfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org,
Piotr Jaroszynski <pjaroszynski@nvidia.com>
Subject: [PATCH] iomap: get/put the page in iomap_page_create/release()
Date: Mon, 21 Jan 2019 16:17:02 +0100 [thread overview]
Message-ID: <20190121151702.28863-1-hch@lst.de> (raw)
From: Piotr Jaroszynski <pjaroszynski@nvidia.com>
migrate_page_move_mapping() expects pages with private data set to have
a page_count elevated by 1. This is what used to happen for xfs through
the buffer_heads code before the switch to iomap in commit 82cb14175e7d
("xfs: add support for sub-pagesize writeback without buffer_heads").
Not having the count elevated causes move_pages() to fail on memory
mapped files coming from xfs.
Make iomap compatible with the migrate_page_move_mapping() assumption by
elevating the page count as part of iomap_page_create() and lowering it
in iomap_page_release().
It causes the move_pages() syscall to misbehave on memory mapped files
from xfs. It does not not move any pages, which I suppose is "just" a
perf issue, but it also ends up returning a positive number which is out
of spec for the syscall. Talking to Michal Hocko, it sounds like
returning positive numbers might be a necessary update to move_pages()
anyway though.
Fixes: 82cb14175e7d ("xfs: add support for sub-pagesize writeback without buffer_heads")
Signed-off-by: Piotr Jaroszynski <pjaroszynski@nvidia.com>
[hch: actually get/put the page iomap_migrate_page() to make it work
properly]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/iomap.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/fs/iomap.c b/fs/iomap.c
index 987fefc054b4..47362397cb82 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -116,6 +116,12 @@ iomap_page_create(struct inode *inode, struct page *page)
atomic_set(&iop->read_count, 0);
atomic_set(&iop->write_count, 0);
bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
+
+ /*
+ * migrate_page_move_mapping() assumes that pages with private data have
+ * their count elevated by 1.
+ */
+ get_page(page);
set_page_private(page, (unsigned long)iop);
SetPagePrivate(page);
return iop;
@@ -132,6 +138,7 @@ iomap_page_release(struct page *page)
WARN_ON_ONCE(atomic_read(&iop->write_count));
ClearPagePrivate(page);
set_page_private(page, 0);
+ put_page(page);
kfree(iop);
}
@@ -569,8 +576,10 @@ iomap_migrate_page(struct address_space *mapping, struct page *newpage,
if (page_has_private(page)) {
ClearPagePrivate(page);
+ get_page(newpage);
set_page_private(newpage, page_private(page));
set_page_private(page, 0);
+ put_page(page);
SetPagePrivate(newpage);
}
--
2.20.1
next reply other threads:[~2019-01-21 15:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-21 15:17 Christoph Hellwig [this message]
2019-01-31 23:28 ` [PATCH] iomap: get/put the page in iomap_page_create/release() Darrick J. Wong
-- strict thread matches above, loose matches on Subject: below --
2018-11-15 0:30 p.jaroszynski
2018-11-15 9:30 ` Christoph Hellwig
2018-11-15 18:44 ` Piotr Jaroszynski
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