[PATCH v4 14/39] netfs: Provide tools to create a buffer in an xarray

David Howells
2023-12-13T15:25:02Z

Provide tools to create a buffer in an xarray, with a function to add new
folios with a mark. This will be used to create bounce buffer and can be
used more easily to create a list of folios the span of which would require
more than a page's worth of bio_vec structs.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
fs/netfs/internal.h | 13 +++++++
fs/netfs/misc.c | 81 +++++++++++++++++++++++++++++++++++++++++++
include/linux/netfs.h | 4 +++
3 files changed, 98 insertions(+)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 937d9a22f178..20eb1fd6986e 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -56,6 +56,19 @@ static inline void netfs_proc_add_rreq(struct netfs_io_request *rreq) {}
static inline void netfs_proc_del_rreq(struct netfs_io_request *rreq) {}
#endif

+/*
+ * misc.c
+ */
+#define NETFS_FLAG_PUT_MARK BIT(0)
+#define NETFS_FLAG_PAGECACHE_MARK BIT(1)
+int netfs_xa_store_and_mark(struct xarray *xa, unsigned long index,
+ struct folio *folio, unsigned int flags,
+ gfp_t gfp_mask);
+int netfs_add_folios_to_buffer(struct xarray *buffer,
+ struct address_space *mapping,
+ pgoff_t index, pgoff_t to, gfp_t gfp_mask);
+void netfs_clear_buffer(struct xarray *buffer);
+
/*
* objects.c
*/
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index d946d85764de..96014c3d1683 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -8,6 +8,87 @@
#include <linux/swap.h>
#include "internal.h"

+/*
+ * Attach a folio to the buffer and maybe set marks on it to say that we need
+ * to put the folio later and twiddle the pagecache flags.
+ */
+int netfs_xa_store_and_mark(struct xarray *xa, unsigned long index,
+ struct folio *folio, unsigned int flags,
+ gfp_t gfp_mask)
+{
+ XA_STATE_ORDER(xas, xa, index, folio_order(folio));
+
+retry:
+ xas_lock(&xas);
+ for (;;) {
+ xas_store(&xas, folio);
+ if (!xas_error(&xas))
+ break;
+ xas_unlock(&xas);
+ if (!xas_nomem(&xas, gfp_mask))
+ return xas_error(&xas);
+ goto retry;
+ }
+
+ if (flags & NETFS_FLAG_PUT_MARK)
+ xas_set_mark(&xas, NETFS_BUF_PUT_MARK);
+ if (flags & NETFS_FLAG_PAGECACHE_MARK)
+ xas_set_mark(&xas, NETFS_BUF_PAGECACHE_MARK);
+ xas_unlock(&xas);
+ return xas_error(&xas);
+}
+
+/*
+ * Create the specified range of folios in the buffer attached to the read
+ * request. The folios are marked with NETFS_BUF_PUT_MARK so that we know that
+ * these need freeing later.
+ */
+int netfs_add_folios_to_buffer(struct xarray *buffer,
+ struct address_space *mapping,
+ pgoff_t index, pgoff_t to, gfp_t gfp_mask)
+{
+ struct folio *folio;
+ int ret;
+
+ if (to + 1 == index) /* Page range is inclusive */
+ return 0;
+
+ do {
+ /* TODO: Figure out what order folio can be allocated here */
+ folio = filemap_alloc_folio(readahead_gfp_mask(mapping), 0);
+ if (!folio)
+ return -ENOMEM;
+ folio->index = index;
+ ret = netfs_xa_store_and_mark(buffer, index, folio,
+ NETFS_FLAG_PUT_MARK, gfp_mask);
+ if (ret < 0) {
+ folio_put(folio);
+ return ret;
+ }
+
+ index += folio_nr_pages(folio);
+ } while (index <= to && index != 0);
+
+ return 0;
+}
+
+/*
+ * Clear an xarray buffer, putting a ref on the folios that have
+ * NETFS_BUF_PUT_MARK set.
+ */
+void netfs_clear_buffer(struct xarray *buffer)
+{
+ struct folio *folio;
+ XA_STATE(xas, buffer, 0);
+
+ rcu_read_lock();
+ xas_for_each_marked(&xas, folio, ULONG_MAX, NETFS_BUF_PUT_MARK) {
+ folio_put(folio);
+ }
+ rcu_read_unlock();
+ xa_destroy(buffer);
+}
+
/**
* netfs_dirty_folio - Mark folio dirty and pin a cache object for writeback
* @mapping: The mapping the folio belongs to.
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index bbb33ccbf719..c05150f51beb 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -109,6 +109,10 @@ static inline int wait_on_page_fscache_killable(struct page *page)
return folio_wait_private_2_killable(page_folio(page));
}

+/* Marks used on xarray-based buffers */
+#define NETFS_BUF_PUT_MARK XA_MARK_0 /* - Page needs putting */
+#define NETFS_BUF_PAGECACHE_MARK XA_MARK_1 /* - Page needs wb/dirty flag wrangling */
+
enum netfs_io_source {
NETFS_FILL_WITH_ZEROES,
NETFS_DOWNLOAD_FROM_SERVER,