For O_DIRECT reads/writes, we check if we need to issue a call to
filemap_write_and_wait_range() to issue and/or wait for writeback for any
page in the given range. The existing mechanism just checks for a page in
the range, which is suboptimal for IOCB_NOWAIT as we'll fallback to the
slow path (and needing retry) if there's just a clean page cache page in
the range.
Provide filemap_range_needs_writeback() which tries a little harder to
check if we actually need to issue and/or wait for writeback in the
range.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/fs.h | 2 ++
mm/filemap.c | 43 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd47deea7c17..def89222dfe9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2633,6 +2633,8 @@ static inline int filemap_fdatawait(struct address_space *mapping)
extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
loff_t lend);
+extern bool filemap_range_needs_writeback(struct address_space *,
+ loff_t lstart, loff_t lend);
extern int filemap_write_and_wait_range(struct address_space *mapping,
loff_t lstart, loff_t lend);
extern int __filemap_fdatawrite_range(struct address_space *mapping,
diff --git a/mm/filemap.c b/mm/filemap.c
index aa0e0fb04670..6a58d50fbd31 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -633,6 +633,49 @@ static bool mapping_needs_writeback(struct address_space *mapping)
return mapping->nrpages;
}
+/**
+ * filemap_range_needs_writeback - check if range potentially needs writeback
+ * @mapping: address space within which to check
+ * @start_byte: offset in bytes where the range starts
+ * @end_byte: offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback. Used by O_DIRECT
+ * read/write with IOCB_NOWAIT, to see if the caller needs to do
+ * filemap_write_and_wait_range() before proceeding.
+ *
+ * Return: %true if the caller should do filemap_write_and_wait_range() before
+ * doing O_DIRECT to a page in this range, %false otherwise.
+ */
+bool filemap_range_needs_writeback(struct address_space *mapping,
+ loff_t start_byte, loff_t end_byte)
+{
+ XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+ pgoff_t max = end_byte >> PAGE_SHIFT;
+ struct page *page;
+
+ if (!mapping_needs_writeback(mapping))
+ return false;
+ if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
+ !mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
+ return false;
+ if (end_byte < start_byte)
+ return false;
+
+ rcu_read_lock();
+ xas_for_each(&xas, page, max) {
+ if (xas_retry(&xas, page))
+ continue;
+ if (xa_is_value(page))
+ continue;
+ if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
+ break;
+ }
+ rcu_read_unlock();
+ return page != NULL;
+}
+EXPORT_SYMBOL_GPL(filemap_range_needs_writeback);
+
/**
* filemap_write_and_wait_range - write out & wait on a file range
* @mapping: the address_space for the pages
--
2.30.0
