[PATCH v2 07/22] mm: Provide a means of invalidation without using launder_folio

David Howells
2024-04-30T14:01:40Z

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.

This is then used from netfslib to handle the flusing in unbuffered and
direct writes.

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
---

Notes:
Changes
=======
ver #2)
- Make filemap_invalidate_inode() take a range.
- Make netfs_unbuffered_write_iter() use filemap_invalidate_inode().

fs/netfs/direct_write.c | 28 ++++++++++++++++++---
include/linux/pagemap.h | 2 ++
mm/filemap.c | 54 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 80 insertions(+), 4 deletions(-)

diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index bee047e20f5d..2b81cd4aae6e 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -132,12 +132,14 @@ static ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov
ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
struct file *file = iocb->ki_filp;
- struct inode *inode = file->f_mapping->host;
+ struct address_space *mapping = file->f_mapping;
+ struct inode *inode = mapping->host;
struct netfs_inode *ictx = netfs_inode(inode);
- unsigned long long end;
ssize_t ret;
+ loff_t pos = iocb->ki_pos;
+ unsigned long long end = pos + iov_iter_count(from) - 1;

- _enter("%llx,%zx,%llx", iocb->ki_pos, iov_iter_count(from), i_size_read(inode));
+ _enter("%llx,%zx,%llx", pos, iov_iter_count(from), i_size_read(inode));

if (!iov_iter_count(from))
return 0;
@@ -157,7 +159,25 @@ ssize_t netfs_unbuffered_write_iter(struct kiocb *iocb, struct iov_iter *from)
ret = file_update_time(file);
if (ret < 0)
goto out;
- ret = kiocb_invalidate_pages(iocb, iov_iter_count(from));
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ /* We could block if there are any pages in the range. */
+ ret = -EAGAIN;
+ if (filemap_range_has_page(mapping, pos, end))
+ if (filemap_invalidate_inode(inode, true, pos, end))
+ goto out;
+ } else {
+ ret = filemap_write_and_wait_range(mapping, pos, end);
+ if (ret < 0)
+ goto out;
+ }
+
+ /*
+ * After a write we want buffered reads to be sure to go to disk to get
+ * the new data. We invalidate clean cached page from the region we're
+ * about to write. We do this *before* the write so that we can return
+ * without clobbering -EIOCBQUEUED from ->direct_IO().
+ */
+ ret = filemap_invalidate_inode(inode, true, pos, end);
if (ret < 0)
goto out;
end = iocb->ki_pos + iov_iter_count(from);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2df35e65557d..c5e33e2ca48a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -40,6 +40,8 @@ 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,
+ loff_t start, loff_t end);

static inline int filemap_fdatawait(struct address_space *mapping)
{
diff --git a/mm/filemap.c b/mm/filemap.c
index 9a2e28bf298a..53516305b4b4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4134,6 +4134,60 @@ bool filemap_release_folio(struct folio *folio, gfp_t gfp)
}
EXPORT_SYMBOL(filemap_release_folio);

+/**
+ * filemap_invalidate_inode - Invalidate/forcibly write back a range of an inode's pagecache
+ * @inode: The inode to flush
+ * @flush: Set to write back rather than simply invalidate.
+ * @start: First byte to in range.
+ * @end: Last byte in range (inclusive), or LLONG_MAX for everything from start
+ * onwards.
+ *
+ * Invalidate all the folios on an inode that contribute to the specified
+ * range, 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,
+ loff_t start, loff_t end)
+{
+ struct address_space *mapping = inode->i_mapping;
+ pgoff_t first = start >> PAGE_SHIFT;
+ pgoff_t last = end >> PAGE_SHIFT;
+ pgoff_t nr = end == LLONG_MAX ? ULONG_MAX : last - first + 1;
+
+ if (!mapping || !mapping->nrpages || end < start)
+ goto out;
+
+ /* Prevent new folios from being added to the inode. */
+ filemap_invalidate_lock(mapping);
+
+ if (!mapping->nrpages)
+ goto unlock;
+
+ unmap_mapping_pages(mapping, first, nr, 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 = first,
+ .range_end = last,
+ };
+
+ filemap_fdatawrite_wbc(mapping, &wbc);
+ }
+
+ /* Wait for writeback to complete on all folios and discard. */
+ truncate_inode_pages_range(mapping, first, last);
+
+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