[PATCH 09/26] mm: Provide a means of invalidation without using launder_folio

David Howells
2024-03-28T16:36:48Z

Implement a replacement for launder_folio. The key feature of
invalidate_inode_pages2() is that it locks each folio individually, unmaps
it to prevent mmap'd accesses interfering and calls the ->launder_folio()
address_space op to flush it. This has problems: firstly, each folio is
written individually as one or more small writes; secondly, adjacent folios
cannot be added so easily into the laundry; thirdly, it's yet another op to
implement.

Instead, use the invalidate lock to cause anyone wanting to add a folio to
the inode to wait, then unmap all the folios if we have mmaps, then,
conditionally, use ->writepages() to flush any dirty data back and then
discard all pages.

The invalidate lock prevents ->read_iter(), ->write_iter() and faulting
through mmap all from adding pages for the duration.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Miklos Szeredi <miklos@szeredi.hu>
cc: Trond Myklebust <trond.myklebust@hammerspace.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Christian Brauner <brauner@kernel.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
cc: netfs@lists.linux.dev
cc: v9fs@lists.linux.dev
cc: linux-afs@lists.infradead.org
cc: ceph-devel@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: devel@lists.orangefs.org
---
include/linux/pagemap.h | 1 +
mm/filemap.c | 46 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 47 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2df35e65557d..4eb3d4177a53 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -40,6 +40,7 @@ int filemap_fdatawait_keep_errors(struct address_space *mapping);
int filemap_fdatawait_range(struct address_space *, loff_t lstart, loff_t lend);
int filemap_fdatawait_range_keep_errors(struct address_space *mapping,
loff_t start_byte, loff_t end_byte);
+int filemap_invalidate_inode(struct inode *inode, bool flush);

static inline int filemap_fdatawait(struct address_space *mapping)
{
diff --git a/mm/filemap.c b/mm/filemap.c
index 25983f0f96e3..087f685107a5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4134,6 +4134,52 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
}
EXPORT_SYMBOL(filemap_release_folio);

+/**
+ * filemap_invalidate_inode - Invalidate/forcibly write back an inode's pagecache
+ * @inode: The inode to flush
+ * @flush: Set to write back rather than simply invalidate.
+ *
+ * Invalidate all the folios on an inode, possibly writing them back first.
+ * Whilst the operation is undertaken, the invalidate lock is held to prevent
+ * new folios from being installed.
+ */
+int filemap_invalidate_inode(struct inode *inode, bool flush)
+{
+ struct address_space *mapping = inode->i_mapping;
+
+ if (!mapping || !mapping->nrpages)
+ goto out;
+
+ /* Prevent new folios from being added to the inode. */
+ filemap_invalidate_lock(mapping);
+
+ if (!mapping->nrpages)
+ goto unlock;
+
+ unmap_mapping_pages(mapping, 0, ULONG_MAX, false);
+
+ /* Write back the data if we're asked to. */
+ if (flush) {
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_ALL,
+ .nr_to_write = LONG_MAX,
+ .range_start = 0,
+ .range_end = LLONG_MAX,
+ };
+
+ filemap_fdatawrite_wbc(mapping, &wbc);
+ }
+
+ /* Wait for writeback to complete on all folios and discard. */
+ truncate_inode_pages_range(mapping, 0, LLONG_MAX);
+
+unlock:
+ filemap_invalidate_unlock(mapping);
+out:
+ return filemap_check_errors(mapping);
+}
+EXPORT_SYMBOL(filemap_invalidate_inode);
+
#ifdef CONFIG_CACHESTAT_SYSCALL
/**
* filemap_cachestat() - compute the page cache statistics of a mapping