[PATCH 09/26] mm: Make readahead store folio count in readahead_control

[David Howells <dhowells@redhat.com>]

Make readahead store folio count in readahead_control so that the
filesystem can know in advance how many folios it needs to keep track of.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: netfs@lists.linux.dev
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
---
 include/linux/pagemap.h | 1 +
 mm/readahead.c          | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index ec442af3f886..3c3e34e5fe8a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -1361,6 +1361,7 @@ struct readahead_control {
 	struct file_ra_state *ra;
 /* private: use the readahead_* accessors instead */
 	pgoff_t _index;
+	unsigned int _nr_folios;
 	unsigned int _nr_pages;
 	unsigned int _batch_count;
 	bool dropbehind;
diff --git a/mm/readahead.c b/mm/readahead.c
index 7b05082c89ea..53134c9d9fe9 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -292,6 +292,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 		if (i == mark)
 			folio_set_readahead(folio);
 		ractl->_workingset |= folio_test_workingset(folio);
+		ractl->_nr_folios++;
 		ractl->_nr_pages += min_nrpages;
 		i += min_nrpages;
 	}
@@ -459,6 +460,7 @@ static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
 		return err;
 	}
 
+	ractl->_nr_folios++;
 	ractl->_nr_pages += 1UL << order;
 	ractl->_workingset |= folio_test_workingset(folio);
 	return 0;
@@ -802,6 +804,7 @@ void readahead_expand(struct readahead_control *ractl,
 			ractl->_workingset = true;
 			psi_memstall_enter(&ractl->_pflags);
 		}
+		ractl->_nr_folios++;
 		ractl->_nr_pages += min_nrpages;
 		ractl->_index = folio->index;
 	}
@@ -831,6 +834,7 @@ void readahead_expand(struct readahead_control *ractl,
 			ractl->_workingset = true;
 			psi_memstall_enter(&ractl->_pflags);
 		}
+		ractl->_nr_folios++;
 		ractl->_nr_pages += min_nrpages;
 		if (ra) {
 			ra->size += min_nrpages;