diff mbox series

[RFC,v2,3/5] mm: Make swap_readpage() for SWP_FS_OPS use ->direct_IO() not ->readpage()

Message ID 162879974434.3306668.4798886633463058599.stgit@warthog.procyon.org.uk (mailing list archive)
State New
Headers show
Series mm: Fix NFS swapfiles and use DIO for swapfiles | expand

Commit Message

David Howells Aug. 12, 2021, 8:22 p.m. UTC 
Make swap_readpage(), when accessing a swap file (SWP_FS_OPS) use
the ->direct_IO() method on the filesystem rather then ->readpage().

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 include/linux/fs.h |    1 
 mm/page_io.c       |  115 +++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 110 insertions(+), 6 deletions(-)

Comments

Matthew Wilcox Aug. 12, 2021, 9:23 p.m. UTC | #1 
On Thu, Aug 12, 2021 at 09:22:24PM +0100, David Howells wrote:
> +++ b/include/linux/fs.h
> @@ -336,6 +336,7 @@ struct kiocb {
>  	union {
>  		unsigned int		ki_cookie; /* for ->iopoll */
>  		struct wait_page_queue	*ki_waitq; /* for async buffered IO */
> +		struct page	*ki_swap_page;	/* For swapfile_read/write */

Nice idea.

> +static void __swapfile_read_complete(struct kiocb *iocb, long ret, long ret2)

I would make this take a struct page * and just one 'ret'.

> +{
> +	struct page *page = iocb->ki_swap_page;
> +
> +	if (ret == PAGE_SIZE) {

page_size(page)?

> +	kiocb.ki_pos		= page_file_offset(page);

We talked about swap_file_pos(), right?

> +	ret = swap_file->f_mapping->a_ops->direct_IO(&kiocb, &to);
> +
> +	__swapfile_read_complete(&kiocb, ret, 0);
> +	return (ret > 0) ? 0 : ret;

What if it returns a short read?

> +static int swapfile_read(struct swap_info_struct *sis, struct page *page,
> +			 bool synchronous)
> +{
> +	struct swapfile_kiocb *ki;
> +	struct file *swap_file = sis->swap_file;
> +	struct bio_vec bv = {
> +		.bv_page = page,
> +		.bv_len  = thp_size(page),
> +		.bv_offset = 0
> +	};
> +	struct iov_iter to;
> +	int ret;
> +
> +	if (synchronous)
> +		return swapfile_read_sync(sis, page);

Seems a shame to set up the bio_vec and iov_iter twice.  Maybe call:

	iov_iter_bvec(&to, READ, &bv, 1, thp_size(page));

before swapfile_read_sync() and pass a pointer to 'to' to
swapfile_read_sync?
Christoph Hellwig Aug. 13, 2021, 7:12 a.m. UTC | #2 
> +/*
> + * Keep track of the kiocb we're using to do async DIO.  We have to
> + * refcount it until various things stop looking at the kiocb *after*
> + * calling ->ki_complete().
> + */
> +struct swapfile_kiocb {
> +	struct kiocb		iocb;
> +	refcount_t		ki_refcnt;
> +};

The ki_ prefix is a little strange here.

> +
> +static void swapfile_put_kiocb(struct swapfile_kiocb *ki)
> +{
> +	if (refcount_dec_and_test(&ki->ki_refcnt)) {
> +		fput(ki->iocb.ki_filp);

What do we need the file reference for here?  The swap code has to have
higher level prevention for closing the file vs active I/O, at least the
block path seems to rely on that.

> +static void swapfile_read_complete(struct kiocb *iocb, long ret, long ret2)
> +{
> +	struct swapfile_kiocb *ki = container_of(iocb, struct swapfile_kiocb, iocb);

Overly long line.

> +	/* Should set IOCB_HIPRI too, but the box becomes unresponsive whilst
> +	 * putting out occasional messages about the NFS sunrpc scheduling
> +	 * tasks being hung.
> +	 */

IOCB_HIPRI has a very specific meaning, so I'm not sure we should
use it never mind leave such a comment here.  Also this is not the
proper standard kernel comment style.

> +
> +	iov_iter_bvec(&to, READ, &bv, 1, thp_size(page));
> +	ret = swap_file->f_mapping->a_ops->direct_IO(&kiocb, &to);
> +
> +	__swapfile_read_complete(&kiocb, ret, 0);
> +	return (ret > 0) ? 0 : ret;

No need for the braces.

> +	return (ret > 0) ? 0 : ret;

Same here.
diff mbox series

Patch

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3e6a20f28ef..94c47b9b5b1c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -336,6 +336,7 @@  struct kiocb {
 	union {
 		unsigned int		ki_cookie; /* for ->iopoll */
 		struct wait_page_queue	*ki_waitq; /* for async buffered IO */
+		struct page	*ki_swap_page;	/* For swapfile_read/write */
 	};
 
 	randomized_struct_fields_end
diff --git a/mm/page_io.c b/mm/page_io.c
index 62cabcdfcec6..92ec4a7b0545 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -26,6 +26,24 @@ 
 #include <linux/uio.h>
 #include <linux/sched/task.h>
 
+/*
+ * Keep track of the kiocb we're using to do async DIO.  We have to
+ * refcount it until various things stop looking at the kiocb *after*
+ * calling ->ki_complete().
+ */
+struct swapfile_kiocb {
+	struct kiocb		iocb;
+	refcount_t		ki_refcnt;
+};
+
+static void swapfile_put_kiocb(struct swapfile_kiocb *ki)
+{
+	if (refcount_dec_and_test(&ki->ki_refcnt)) {
+		fput(ki->iocb.ki_filp);
+		kfree(ki);
+	}
+}
+
 static void end_swap_bio_write(struct bio *bio)
 {
 	struct page *page = bio_first_page_all(bio);
@@ -353,6 +371,96 @@  int __swap_writepage(struct page *page, struct writeback_control *wbc)
 	return 0;
 }
 
+static void __swapfile_read_complete(struct kiocb *iocb, long ret, long ret2)
+{
+	struct page *page = iocb->ki_swap_page;
+
+	if (ret == PAGE_SIZE) {
+		count_vm_event(PSWPIN);
+		SetPageUptodate(page);
+	} else {
+		SetPageError(page);
+		pr_err_ratelimited("Read error (%ld) on dio swapfile (%llu)\n",
+				   ret, page_file_offset(page));
+	}
+
+	unlock_page(page);
+}
+
+static void swapfile_read_complete(struct kiocb *iocb, long ret, long ret2)
+{
+	struct swapfile_kiocb *ki = container_of(iocb, struct swapfile_kiocb, iocb);
+
+	__swapfile_read_complete(iocb, ret, ret2);
+	swapfile_put_kiocb(ki);
+}
+
+static int swapfile_read_sync(struct swap_info_struct *sis, struct page *page)
+{
+	struct kiocb kiocb;
+	struct file *swap_file = sis->swap_file;
+	struct bio_vec bv = {
+		.bv_page	= page,
+		.bv_len		= thp_size(page),
+		.bv_offset	= 0
+	};
+	struct iov_iter to;
+	int ret;
+
+	init_sync_kiocb(&kiocb, swap_file);
+	kiocb.ki_swap_page	= page;
+	kiocb.ki_pos		= page_file_offset(page);
+	kiocb.ki_filp		= swap_file;
+	kiocb.ki_flags		= IOCB_DIRECT | IOCB_SWAP;
+	/* Should set IOCB_HIPRI too, but the box becomes unresponsive whilst
+	 * putting out occasional messages about the NFS sunrpc scheduling
+	 * tasks being hung.
+	 */
+
+	iov_iter_bvec(&to, READ, &bv, 1, thp_size(page));
+	ret = swap_file->f_mapping->a_ops->direct_IO(&kiocb, &to);
+
+	__swapfile_read_complete(&kiocb, ret, 0);
+	return (ret > 0) ? 0 : ret;
+}
+
+static int swapfile_read(struct swap_info_struct *sis, struct page *page,
+			 bool synchronous)
+{
+	struct swapfile_kiocb *ki;
+	struct file *swap_file = sis->swap_file;
+	struct bio_vec bv = {
+		.bv_page = page,
+		.bv_len  = thp_size(page),
+		.bv_offset = 0
+	};
+	struct iov_iter to;
+	int ret;
+
+	if (synchronous)
+		return swapfile_read_sync(sis, page);
+
+	ki = kzalloc(sizeof(*ki), GFP_KERNEL);
+	if (!ki)
+		return -ENOMEM;
+
+	refcount_set(&ki->ki_refcnt, 2);
+	init_sync_kiocb(&ki->iocb, swap_file);
+	ki->iocb.ki_swap_page	= page;
+	ki->iocb.ki_flags	= IOCB_DIRECT | IOCB_SWAP;
+	ki->iocb.ki_pos		= page_file_offset(page);
+	ki->iocb.ki_filp	= get_file(swap_file);
+	ki->iocb.ki_complete	= swapfile_read_complete;
+
+	iov_iter_bvec(&to, READ, &bv, 1, thp_size(page));
+	ret = swap_file->f_mapping->a_ops->direct_IO(&ki->iocb, &to);
+
+	if (ret != -EIOCBQUEUED)
+		swapfile_read_complete(&ki->iocb, ret, 0);
+	swapfile_put_kiocb(ki);
+	return (ret > 0) ? 0 : ret;
+}
+
 int swap_readpage(struct page *page, bool synchronous)
 {
 	struct bio *bio;
@@ -380,12 +488,7 @@  int swap_readpage(struct page *page, bool synchronous)
 	}
 
 	if (data_race(sis->flags & SWP_FS_OPS)) {
-		struct file *swap_file = sis->swap_file;
-		struct address_space *mapping = swap_file->f_mapping;
-
-		ret = mapping->a_ops->readpage(swap_file, page);
-		if (!ret)
-			count_vm_event(PSWPIN);
+		ret = swapfile_read(sis, page, synchronous);
 		goto out;
 	}