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From: David Howells <dhowells@redhat.com>
In-Reply-To: <2318298.1711551844@warthog.procyon.org.uk>
References: <2318298.1711551844@warthog.procyon.org.uk>
To: dhowells@redhat.com
Cc: Matthew Wilcox <willy@infradead.org>,
    Miklos Szeredi <miklos@szeredi.hu>,
    Trond Myklebust <trond.myklebust@hammerspace.com>,
    Christoph Hellwig <hch@lst.de>,
    Andrew Morton <akpm@linux-foundation.org>,
    Alexander Viro <viro@zeniv.linux.org.uk>,
    Christian Brauner <brauner@kernel.org>,
    Jeff Layton <jlayton@kernel.org>, linux-mm@kvack.org,
    linux-fsdevel@vger.kernel.org, netfs@lists.linux.dev,
    v9fs@lists.linux.dev, linux-afs@lists.infradead.org,
    ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org,
    linux-nfs@vger.kernel.org, devel@lists.orangefs.org,
    linux-kernel@vger.kernel.org
Subject: [RFC PATCH v2] mm, netfs: Provide a means of invalidation without using launder_folio
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Date: Wed, 27 Mar 2024 17:55:45 +0000
Message-ID: <2506007.1711562145@warthog.procyon.org.uk>

mm, netfs: Provide a means of invalidation without using launder_folio

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 folio=
s
cannot be added so easily into the laundry; thirdly, it's yet another op t=
o
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            |   48 ++++++++++++++++++++++++++++++++++++++++++=
++++++
 2 files changed, 49 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..98f439bedb44 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4134,6 +4134,54 @@ 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 p=
agecache
+ * @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 firs=
t.
+ * Whilst the operation is undertaken, the invalidate lock is held to pre=
vent
+ * new folios from being installed.
+ */
+int filemap_invalidate_inode(struct inode *inode, bool flush)
+{
+	struct address_space *mapping =3D 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;
+
+	/* Assume there are probably PTEs only if there are mmaps. */
+	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
+		unmap_mapping_pages(mapping, 0, ULONG_MAX, false);
+
+	/* Write back the data if we're asked to. */
+	if (flush) {
+		struct writeback_control wbc =3D {
+			.sync_mode	=3D WB_SYNC_ALL,
+			.nr_to_write	=3D LONG_MAX,
+			.range_start	=3D 0,
+			.range_end	=3D 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