[PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes

Jens Axboe
2019-12-10T20:43:24Z

This adds support for RWF_UNCACHED for file systems using iomap to
perform buffered writes. We use the generic infrastructure for this,
by tracking pages we created and calling write_drop_cached_pages()
to issue writeback and prune those pages.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/iomap/buffered-io.c | 72 +++++++++++++++++++++++++++++++++++-------
include/linux/iomap.h | 1 +
2 files changed, 62 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 9b5b770ca4c7..3a18a6af8cb3 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -17,6 +17,7 @@
#include <linux/bio.h>
#include <linux/sched/signal.h>
#include <linux/migrate.h>
+#include <linux/pagevec.h>
#include "trace.h"

#include "../internal.h"
@@ -566,6 +567,7 @@ EXPORT_SYMBOL_GPL(iomap_migrate_page);

enum {
IOMAP_WRITE_F_UNSHARE = (1 << 0),
+ IOMAP_WRITE_F_UNCACHED = (1 << 1),
};

static void
@@ -643,6 +645,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
{
const struct iomap_page_ops *page_ops = iomap->page_ops;
+ unsigned aop_flags;
struct page *page;
int status = 0;

@@ -659,8 +662,11 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
return status;
}

+ aop_flags = AOP_FLAG_NOFS;
+ if (flags & IOMAP_UNCACHED)
+ aop_flags |= AOP_FLAG_UNCACHED;
page = grab_cache_page_write_begin(inode->i_mapping, pos >> PAGE_SHIFT,
- AOP_FLAG_NOFS);
+ aop_flags);
if (!page) {
status = -ENOMEM;
goto out_no_page;
@@ -670,9 +676,14 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
iomap_read_inline_data(inode, page, srcmap);
else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
status = __block_write_begin_int(page, pos, len, NULL, srcmap);
- else
- status = __iomap_write_begin(inode, pos, len, flags, page,
+ else {
+ unsigned wb_flags = 0;
+
+ if (flags & IOMAP_UNCACHED)
+ wb_flags = IOMAP_WRITE_F_UNCACHED;
+ status = __iomap_write_begin(inode, pos, len, wb_flags, page,
srcmap);
+ }

if (unlikely(status))
goto out_unlock;
@@ -796,19 +807,27 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len, unsigned copied,
return ret;
}

+#define GPW_PAGE_BATCH 16
+
static loff_t
iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
unsigned flags, struct iomap *iomap, struct iomap *srcmap)
{
+ struct address_space *mapping = inode->i_mapping;
struct iov_iter *i = data;
+ struct pagevec pvec;
long status = 0;
ssize_t written = 0;

+ pagevec_init(&pvec);
+
do {
struct page *page;
unsigned long offset; /* Offset into pagecache page */
unsigned long bytes; /* Bytes to write to page */
size_t copied; /* Bytes copied from user */
+ bool drop_page = false; /* drop page after IO */
+ unsigned lflags = flags;

offset = offset_in_page(pos);
bytes = min_t(unsigned long, PAGE_SIZE - offset,
@@ -832,10 +851,17 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
break;
}

- status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap,
- srcmap);
- if (unlikely(status))
+retry:
+ status = iomap_write_begin(inode, pos, bytes, lflags, &page,
+ iomap, srcmap);
+ if (unlikely(status)) {
+ if (status == -ENOMEM && (lflags & IOMAP_UNCACHED)) {
+ drop_page = true;
+ lflags &= ~IOMAP_UNCACHED;
+ goto retry;
+ }
break;
+ }

if (mapping_writably_mapped(inode->i_mapping))
flush_dcache_page(page);
@@ -844,10 +870,16 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,

flush_dcache_page(page);

+ if (drop_page)
+ get_page(page);
+
status = iomap_write_end(inode, pos, bytes, copied, page, iomap,
srcmap);
- if (unlikely(status < 0))
+ if (unlikely(status < 0)) {
+ if (drop_page)
+ put_page(page);
break;
+ }
copied = status;

cond_resched();
@@ -864,15 +896,29 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
*/
bytes = min_t(unsigned long, PAGE_SIZE - offset,
iov_iter_single_seg_count(i));
+ if (drop_page)
+ put_page(page);
goto again;
}
+
+ if (drop_page &&
+ ((pos >> PAGE_SHIFT) != ((pos + copied) >> PAGE_SHIFT))) {
+ if (!pagevec_add(&pvec, page))
+ write_drop_cached_pages(&pvec, mapping);
+ } else {
+ if (drop_page)
+ put_page(page);
+ balance_dirty_pages_ratelimited(inode->i_mapping);
+ }
+
pos += copied;
written += copied;
length -= copied;
-
- balance_dirty_pages_ratelimited(inode->i_mapping);
} while (iov_iter_count(i) && length);

+ if (pagevec_count(&pvec))
+ write_drop_cached_pages(&pvec, mapping);
+
return written ? written : status;
}

@@ -882,10 +928,14 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
{
struct inode *inode = iocb->ki_filp->f_mapping->host;
loff_t pos = iocb->ki_pos, ret = 0, written = 0;
+ unsigned flags = IOMAP_WRITE;
+
+ if (iocb->ki_flags & IOCB_UNCACHED)
+ flags |= IOMAP_UNCACHED;

while (iov_iter_count(iter)) {
- ret = iomap_apply(inode, pos, iov_iter_count(iter),
- IOMAP_WRITE, ops, iter, iomap_write_actor);
+ ret = iomap_apply(inode, pos, iov_iter_count(iter), flags,
+ ops, iter, iomap_write_actor);
if (ret <= 0)
break;
pos += ret;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 61fcaa3904d4..833dd43507ac 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -121,6 +121,7 @@ struct iomap_page_ops {
#define IOMAP_FAULT (1 << 3) /* mapping for page fault */
#define IOMAP_DIRECT (1 << 4) /* direct I/O */
#define IOMAP_NOWAIT (1 << 5) /* do not block */
+#define IOMAP_UNCACHED (1 << 6)

struct iomap_ops {
/*
--
2.24.0