The migration code used to be able to migrate dirty 9p folios by writing them back using writepage. When the writepage method was removed, we neglected to add a migrate_folio method, which means that dirty 9p folios have been unmovable ever since. This reduced our success at defragmenting memory on machines which use 9p heavily.
Fixes: 80105ed2fd27 (9p: Use netfslib read/write_iter) Cc: stable@vger.kernel.org Cc: David Howells dhowells@redhat.com Cc: v9fs@lists.linux.dev Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org --- fs/9p/vfs_addr.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c index 32619d146cbc..1286d96a29bc 100644 --- a/fs/9p/vfs_addr.c +++ b/fs/9p/vfs_addr.c @@ -164,4 +164,5 @@ const struct address_space_operations v9fs_addr_operations = { .invalidate_folio = netfs_invalidate_folio, .direct_IO = noop_direct_IO, .writepages = netfs_writepages, + .migrate_folio = filemap_migrate_folio, };
Matthew Wilcox (Oracle) willy@infradead.org wrote:
The migration code used to be able to migrate dirty 9p folios by writing them back using writepage. When the writepage method was removed, we neglected to add a migrate_folio method, which means that dirty 9p folios have been unmovable ever since. This reduced our success at defragmenting memory on machines which use 9p heavily.
Fixes: 80105ed2fd27 (9p: Use netfslib read/write_iter) Cc: stable@vger.kernel.org Cc: David Howells dhowells@redhat.com Cc: v9fs@lists.linux.dev Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org
Reviewed-by: David Howells dhowells@redhat.com
Matthew Wilcox (Oracle) wrote on Wed, Apr 02, 2025 at 03:59:55PM +0100:
The migration code used to be able to migrate dirty 9p folios by writing them back using writepage. When the writepage method was removed, we neglected to add a migrate_folio method, which means that dirty 9p folios have been unmovable ever since. This reduced our success at defragmenting memory on machines which use 9p heavily.
Fixes: 80105ed2fd27 (9p: Use netfslib read/write_iter) Cc: stable@vger.kernel.org Cc: David Howells dhowells@redhat.com Cc: v9fs@lists.linux.dev Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org
Given I'm not in Cc of the whole series I'm lacking context but I assume that means I'm not supposed to take this in.
I won't pretend I understand folios anyway, but commit messages makes sense to me: Acked-by: Dominique Martinet asmadeus@codewreck.org
Thanks,
On Thu, Apr 03, 2025 at 12:46:17PM +0900, Dominique Martinet wrote:
Matthew Wilcox (Oracle) wrote on Wed, Apr 02, 2025 at 03:59:55PM +0100:
The migration code used to be able to migrate dirty 9p folios by writing them back using writepage. When the writepage method was removed, we neglected to add a migrate_folio method, which means that dirty 9p folios have been unmovable ever since. This reduced our success at defragmenting memory on machines which use 9p heavily.
Given I'm not in Cc of the whole series I'm lacking context but I assume that means I'm not supposed to take this in.
Right; I'm routing this whole series via Christian. There's various bits of the VFS that need to be touched as part of this series, and it'd take forever to get it all merged by going through individual maintainer trees.
I won't pretend I understand folios anyway, but commit messages makes sense to me: Acked-by: Dominique Martinet asmadeus@codewreck.org
Thanks! Folios aren't really that hard a concept for a filesystem developer to understand, but dhowells has done a great job of insulating you from even having to understand them with netfs. All they are is a container of one-or-more pages which maintain all the filesystem state which used to be managed per-page. eg dirty, writeback, locked, offset-in-file, number-of-mappings.
There's more to it from a MM point of view, but as a filesystem developer, that's all you really need to understand.
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Matthew Wilcox (Oracle)