linux-kernel - [RFC PATCH v2] mm, netfs: Provide a means of invalidation without using launder

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Message-ID: <2506007.1711562145@warthog.procyon.org.uk>
Date: Wed, 27 Mar 2024 17:55:45 +0000
From: David Howells <dhowells@...hat.com>
To: dhowells@...hat.com
Cc: Matthew Wilcox <willy@...radead.org>,
    Miklos Szeredi <miklos@...redi.hu>,
    Trond Myklebust <trond.myklebust@...merspace.com>,
    Christoph Hellwig <hch@....de>,
    Andrew Morton <akpm@...ux-foundation.org>,
    Alexander Viro <viro@...iv.linux.org.uk>,
    Christian Brauner <brauner@...nel.org>,
    Jeff Layton <jlayton@...nel.org>, linux-mm@...ck.org,
    linux-fsdevel@...r.kernel.org, netfs@...ts.linux.dev,
    v9fs@...ts.linux.dev, linux-afs@...ts.infradead.org,
    ceph-devel@...r.kernel.org, linux-cifs@...r.kernel.org,
    linux-nfs@...r.kernel.org, devel@...ts.orangefs.org,
    linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2] mm, netfs: Provide a means of invalidation without using launder_folio

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 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@...hat.com>
cc: Matthew Wilcox <willy@...radead.org>
cc: Miklos Szeredi <miklos@...redi.hu>
cc: Trond Myklebust <trond.myklebust@...merspace.com>
cc: Christoph Hellwig <hch@....de>
cc: Andrew Morton <akpm@...ux-foundation.org>
cc: Alexander Viro <viro@...iv.linux.org.uk>
cc: Christian Brauner <brauner@...nel.org>
cc: Jeff Layton <jlayton@...nel.org>
cc: linux-mm@...ck.org
cc: linux-fsdevel@...r.kernel.org
cc: netfs@...ts.linux.dev
cc: v9fs@...ts.linux.dev
cc: linux-afs@...ts.infradead.org
cc: ceph-devel@...r.kernel.org
cc: linux-cifs@...r.kernel.org
cc: linux-nfs@...r.kernel.org
cc: devel@...ts.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 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;
+
+	/* 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 = {
+			.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