[PATCH v3 8/8] iomap: Copy larger chunks from userspace

Matthew Wilcox (Oracle)
2023-06-12T20:39:52Z

If we have a large folio, we can copy in larger chunks than PAGE_SIZE.
Start at the maximum page cache size and shrink by half every time we
hit the "we are short on memory" problem.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/iomap/buffered-io.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index a5d62c9640cf..818dc350ffc5 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -768,6 +768,7 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
{
loff_t length = iomap_length(iter);
+ size_t chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
loff_t pos = iter->pos;
ssize_t written = 0;
long status = 0;
@@ -776,15 +777,13 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)

do {
struct folio *folio;
- struct page *page;
- unsigned long offset; /* Offset into pagecache page */
- unsigned long bytes; /* Bytes to write to page */
+ size_t offset; /* Offset into folio */
+ unsigned long bytes; /* Bytes to write to folio */
size_t copied; /* Bytes copied from user */

- offset = offset_in_page(pos);
- bytes = min_t(unsigned long, PAGE_SIZE - offset,
- iov_iter_count(i));
again:
+ offset = pos & (chunk - 1);
+ bytes = min(chunk - offset, iov_iter_count(i));
status = balance_dirty_pages_ratelimited_flags(mapping,
bdp_flags);
if (unlikely(status))
@@ -814,11 +813,14 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
if (iter->iomap.flags & IOMAP_F_STALE)
break;

- page = folio_file_page(folio, pos >> PAGE_SHIFT);
+ offset = offset_in_folio(folio, pos);
+ if (bytes > folio_size(folio) - offset)
+ bytes = folio_size(folio) - offset;
+
if (mapping_writably_mapped(mapping))
- flush_dcache_page(page);
+ flush_dcache_folio(folio);

- copied = copy_page_from_iter_atomic(page, offset, bytes, i);
+ copied = copy_page_from_iter_atomic(&folio->page, offset, bytes, i);

status = iomap_write_end(iter, pos, bytes, copied, folio);

@@ -835,6 +837,8 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
*/
if (copied)
bytes = copied;
+ if (chunk > PAGE_SIZE)
+ chunk /= 2;
goto again;
}
pos += status;
--
2.39.2