On 28.04.23 14:41, Jan Kara wrote:
If the page is pinned, there's no point in trying to reclaim it.
Furthermore if the page is from the page cache we don't want to reclaim
fs-private data from the page because the pinning process may be writing
to the page at any time and reclaiming fs private info on a dirty page
can upset the filesystem (see link below).
Link: https://lore.kernel.org/linux-mm/20180103100430.GE4911@xxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
mm/vmscan.c | 10 ++++++++++
1 file changed, 10 insertions(+)
This was the non-controversial part of my series [1] dealing with pinned pages
in filesystems. It is already a win as it avoids crashes in the filesystem and
we can drop workarounds for this in ext4. Can we merge it please?
[1] https://lore.kernel.org/all/20230209121046.25360-1-jack@xxxxxxx/
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bf3eedf0209c..401a379ea99a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1901,6 +1901,16 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
}
}
+ /*
+ * Folio is unmapped now so it cannot be newly pinned anymore.
+ * No point in trying to reclaim folio if it is pinned.
+ * Furthermore we don't want to reclaim underlying fs metadata
+ * if the folio is pinned and thus potentially modified by the
+ * pinning process as that may upset the filesystem.
+ */
+ if (folio_maybe_dma_pinned(folio))
+ goto activate_locked;
+
mapping = folio_mapping(folio);
if (folio_test_dirty(folio)) {
/*
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Thanks!
--
Thanks,
David / dhildenb
