diff mbox series

[09/10] MM: submit multipage write for SWP_FS_OPS swap-space

Message ID 164859778128.29473.5191868522654408537.stgit@noble.brown (mailing list archive)
State New, archived
Headers show
Series MM changes to improve swap-over-NFS support | expand

Commit Message

NeilBrown March 29, 2022, 11:49 p.m. UTC 
swap_writepage() is given one page at a time, but may be called repeatedly
in succession.
For block-device swapspace, the blk_plug functionality allows the
multiple pages to be combined together at lower layers.
That cannot be used for SWP_FS_OPS as blk_plug may not exist - it is
only active when CONFIG_BLOCK=y.  Consequently all swap reads over NFS
are single page reads.

With this patch we pass a pointer-to-pointer via the wbc.
swap_writepage can store state between calls - much like the pointer
passed explicitly to swap_readpage.  After calling swap_writepage() some
number of times, the state will be passed to swap_write_unplug() which
can submit the combined request.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 include/linux/writeback.h |    7 ++++
 mm/page_io.c              |   78 ++++++++++++++++++++++++++++++++-------------
 mm/swap.h                 |    4 ++
 mm/vmscan.c               |    9 ++++-
 4 files changed, 74 insertions(+), 24 deletions(-)

Comments

Miaohe Lin April 18, 2022, 6:59 a.m. UTC | #1 
On 2022/3/30 7:49, NeilBrown wrote:
> swap_writepage() is given one page at a time, but may be called repeatedly
> in succession.
> For block-device swapspace, the blk_plug functionality allows the
> multiple pages to be combined together at lower layers.
> That cannot be used for SWP_FS_OPS as blk_plug may not exist - it is
> only active when CONFIG_BLOCK=y.  Consequently all swap reads over NFS
> are single page reads.
> 
> With this patch we pass a pointer-to-pointer via the wbc.
> swap_writepage can store state between calls - much like the pointer
> passed explicitly to swap_readpage.  After calling swap_writepage() some
> number of times, the state will be passed to swap_write_unplug() which
> can submit the combined request.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: NeilBrown <neilb@suse.de>
...
>  
>  static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
>  {
> -	struct swap_iocb *sio;
> +	struct swap_iocb *sio = NULL;
>  	struct swap_info_struct *sis = page_swap_info(page);
>  	struct file *swap_file = sis->swap_file;
> -	struct address_space *mapping = swap_file->f_mapping;
> -	struct iov_iter from;
> -	int ret;
> +	loff_t pos = page_file_offset(page);
>  
>  	set_page_writeback(page);
>  	unlock_page(page);
> -	sio = mempool_alloc(sio_pool, GFP_NOIO);
> -	init_sync_kiocb(&sio->iocb, swap_file);
> -	sio->iocb.ki_complete = sio_write_complete;
> -	sio->iocb.ki_pos = page_file_offset(page);
> -	sio->bvec[0].bv_page = page;
> -	sio->bvec[0].bv_len = PAGE_SIZE;
> -	sio->bvec[0].bv_offset = 0;
> -	iov_iter_bvec(&from, WRITE, &sio->bvec[0], 1, PAGE_SIZE);
> -	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
> -	if (ret != -EIOCBQUEUED)
> -		sio_write_complete(&sio->iocb, ret);
> -	return ret;
> +	if (wbc->swap_plug)
> +		sio = *wbc->swap_plug;
> +	if (sio) {
> +		if (sio->iocb.ki_filp != swap_file ||
> +		    sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
> +			swap_write_unplug(sio);
> +			sio = NULL;
> +		}
> +	}
> +	if (!sio) {
> +		sio = mempool_alloc(sio_pool, GFP_NOIO);
> +		init_sync_kiocb(&sio->iocb, swap_file);
> +		sio->iocb.ki_complete = sio_write_complete;
> +		sio->iocb.ki_pos = pos;
> +		sio->pages = 0;
> +	}
> +	sio->bvec[sio->pages].bv_page = page;
> +	sio->bvec[sio->pages].bv_len = PAGE_SIZE;

Many thanks for your patch. And sorry for late responding and newbie question. Does swap_writepage_fs
support transhuge page now? We could come across transhuge page here. But bv_len == PAGE_SIZE and pages
== 1 is assumed here. Do we need something like below:

sio->bvec[sio->pages].bv_len = thp_size(page);
sio->pages += thp_nr_pages(page);

Thanks! :)

> +	sio->bvec[sio->pages].bv_offset = 0;
...
> .
>
NeilBrown April 26, 2022, 1:58 a.m. UTC | #2 
On Mon, 18 Apr 2022, Miaohe Lin wrote:
> On 2022/3/30 7:49, NeilBrown wrote:
> > swap_writepage() is given one page at a time, but may be called repeatedly
> > in succession.
> > For block-device swapspace, the blk_plug functionality allows the
> > multiple pages to be combined together at lower layers.
> > That cannot be used for SWP_FS_OPS as blk_plug may not exist - it is
> > only active when CONFIG_BLOCK=y.  Consequently all swap reads over NFS
> > are single page reads.
> > 
> > With this patch we pass a pointer-to-pointer via the wbc.
> > swap_writepage can store state between calls - much like the pointer
> > passed explicitly to swap_readpage.  After calling swap_writepage() some
> > number of times, the state will be passed to swap_write_unplug() which
> > can submit the combined request.
> > 
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: NeilBrown <neilb@suse.de>
> ...
> >  
> >  static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
> >  {
> > -	struct swap_iocb *sio;
> > +	struct swap_iocb *sio = NULL;
> >  	struct swap_info_struct *sis = page_swap_info(page);
> >  	struct file *swap_file = sis->swap_file;
> > -	struct address_space *mapping = swap_file->f_mapping;
> > -	struct iov_iter from;
> > -	int ret;
> > +	loff_t pos = page_file_offset(page);
> >  
> >  	set_page_writeback(page);
> >  	unlock_page(page);
> > -	sio = mempool_alloc(sio_pool, GFP_NOIO);
> > -	init_sync_kiocb(&sio->iocb, swap_file);
> > -	sio->iocb.ki_complete = sio_write_complete;
> > -	sio->iocb.ki_pos = page_file_offset(page);
> > -	sio->bvec[0].bv_page = page;
> > -	sio->bvec[0].bv_len = PAGE_SIZE;
> > -	sio->bvec[0].bv_offset = 0;
> > -	iov_iter_bvec(&from, WRITE, &sio->bvec[0], 1, PAGE_SIZE);
> > -	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
> > -	if (ret != -EIOCBQUEUED)
> > -		sio_write_complete(&sio->iocb, ret);
> > -	return ret;
> > +	if (wbc->swap_plug)
> > +		sio = *wbc->swap_plug;
> > +	if (sio) {
> > +		if (sio->iocb.ki_filp != swap_file ||
> > +		    sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
> > +			swap_write_unplug(sio);
> > +			sio = NULL;
> > +		}
> > +	}
> > +	if (!sio) {
> > +		sio = mempool_alloc(sio_pool, GFP_NOIO);
> > +		init_sync_kiocb(&sio->iocb, swap_file);
> > +		sio->iocb.ki_complete = sio_write_complete;
> > +		sio->iocb.ki_pos = pos;
> > +		sio->pages = 0;
> > +	}
> > +	sio->bvec[sio->pages].bv_page = page;
> > +	sio->bvec[sio->pages].bv_len = PAGE_SIZE;
> 
> Many thanks for your patch. And sorry for late responding and newbie question. Does swap_writepage_fs
> support transhuge page now? We could come across transhuge page here. But bv_len == PAGE_SIZE and pages
> == 1 is assumed here. Do we need something like below:
> 
> sio->bvec[sio->pages].bv_len = thp_size(page);
> sio->pages += thp_nr_pages(page);

Yes, that probably makes sense.  I'll have a closer look and maybe
resend later this week.

Thanks,
NeilBrown


> 
> Thanks! :)
> 
> > +	sio->bvec[sio->pages].bv_offset = 0;
> ...
> > .
> > 
> 
>
diff mbox series

Patch

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index fec248ab1fec..32b35f21cb97 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -80,6 +80,13 @@  struct writeback_control {
 
 	unsigned punt_to_cgroup:1;	/* cgrp punting, see __REQ_CGROUP_PUNT */
 
+	/* To enable batching of swap writes to non-block-device backends,
+	 * "plug" can be set point to a 'struct swap_iocb *'.  When all swap
+	 * writes have been submitted, if with swap_iocb is not NULL,
+	 * swap_write_unplug() should be called.
+	 */
+	struct swap_iocb **swap_plug;
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct bdi_writeback *wb;	/* wb this writeback is issued under */
 	struct inode *inode;		/* inode being written out */
diff --git a/mm/page_io.c b/mm/page_io.c
index 8735707ea349..6eeec8692a29 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -308,8 +308,9 @@  static void sio_write_complete(struct kiocb *iocb, long ret)
 {
 	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
 	struct page *page = sio->bvec[0].bv_page;
+	int p;
 
-	if (ret != PAGE_SIZE) {
+	if (ret != PAGE_SIZE * sio->pages) {
 		/*
 		 * In the case of swap-over-nfs, this can be a
 		 * temporary failure if the system has limited
@@ -320,43 +321,63 @@  static void sio_write_complete(struct kiocb *iocb, long ret)
 		 * the normal direct-to-bio case as it could
 		 * be temporary.
 		 */
-		set_page_dirty(page);
-		ClearPageReclaim(page);
 		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
 				   ret, page_file_offset(page));
+		for (p = 0; p < sio->pages; p++) {
+			page = sio->bvec[p].bv_page;
+			set_page_dirty(page);
+			ClearPageReclaim(page);
+		}
 	} else
-		count_vm_event(PSWPOUT);
-	end_page_writeback(page);
+		count_vm_events(PSWPOUT, sio->pages);
+
+	for (p = 0; p < sio->pages; p++)
+		end_page_writeback(sio->bvec[p].bv_page);
+
 	mempool_free(sio, sio_pool);
 }
 
 static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
 {
-	struct swap_iocb *sio;
+	struct swap_iocb *sio = NULL;
 	struct swap_info_struct *sis = page_swap_info(page);
 	struct file *swap_file = sis->swap_file;
-	struct address_space *mapping = swap_file->f_mapping;
-	struct iov_iter from;
-	int ret;
+	loff_t pos = page_file_offset(page);
 
 	set_page_writeback(page);
 	unlock_page(page);
-	sio = mempool_alloc(sio_pool, GFP_NOIO);
-	init_sync_kiocb(&sio->iocb, swap_file);
-	sio->iocb.ki_complete = sio_write_complete;
-	sio->iocb.ki_pos = page_file_offset(page);
-	sio->bvec[0].bv_page = page;
-	sio->bvec[0].bv_len = PAGE_SIZE;
-	sio->bvec[0].bv_offset = 0;
-	iov_iter_bvec(&from, WRITE, &sio->bvec[0], 1, PAGE_SIZE);
-	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
-	if (ret != -EIOCBQUEUED)
-		sio_write_complete(&sio->iocb, ret);
-	return ret;
+	if (wbc->swap_plug)
+		sio = *wbc->swap_plug;
+	if (sio) {
+		if (sio->iocb.ki_filp != swap_file ||
+		    sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
+			swap_write_unplug(sio);
+			sio = NULL;
+		}
+	}
+	if (!sio) {
+		sio = mempool_alloc(sio_pool, GFP_NOIO);
+		init_sync_kiocb(&sio->iocb, swap_file);
+		sio->iocb.ki_complete = sio_write_complete;
+		sio->iocb.ki_pos = pos;
+		sio->pages = 0;
+	}
+	sio->bvec[sio->pages].bv_page = page;
+	sio->bvec[sio->pages].bv_len = PAGE_SIZE;
+	sio->bvec[sio->pages].bv_offset = 0;
+	sio->pages += 1;
+	if (sio->pages == ARRAY_SIZE(sio->bvec) || !wbc->swap_plug) {
+		swap_write_unplug(sio);
+		sio = NULL;
+	}
+	if (wbc->swap_plug)
+		*wbc->swap_plug = sio;
+
+	return 0;
 }
 
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
-		bio_end_io_t end_write_func)
+		     bio_end_io_t end_write_func)
 {
 	struct bio *bio;
 	int ret;
@@ -393,6 +414,19 @@  int __swap_writepage(struct page *page, struct writeback_control *wbc,
 	return 0;
 }
 
+void swap_write_unplug(struct swap_iocb *sio)
+{
+	struct iov_iter from;
+	struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
+	int ret;
+
+	iov_iter_bvec(&from, WRITE, sio->bvec, sio->pages,
+		      PAGE_SIZE * sio->pages);
+	ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
+	if (ret != -EIOCBQUEUED)
+		sio_write_complete(&sio->iocb, ret);
+}
+
 static void sio_read_complete(struct kiocb *iocb, long ret)
 {
 	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
diff --git a/mm/swap.h b/mm/swap.h
index 0389ab147837..a6da8f612904 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -16,6 +16,7 @@  static inline void swap_read_unplug(struct swap_iocb *plug)
 	if (unlikely(plug))
 		__swap_read_unplug(plug);
 }
+void swap_write_unplug(struct swap_iocb *sio);
 int swap_writepage(struct page *page, struct writeback_control *wbc);
 void end_swap_bio_write(struct bio *bio);
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
@@ -71,6 +72,9 @@  static inline int swap_readpage(struct page *page, bool do_poll,
 {
 	return 0;
 }
+static inline void swap_write_unplug(struct swap_iocb *sio)
+{
+}
 
 static inline struct address_space *swap_address_space(swp_entry_t entry)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9150754bf2b8..658724af15c7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1156,7 +1156,8 @@  typedef enum {
  * pageout is called by shrink_page_list() for each dirty page.
  * Calls ->writepage().
  */
-static pageout_t pageout(struct folio *folio, struct address_space *mapping)
+static pageout_t pageout(struct folio *folio, struct address_space *mapping,
+			 struct swap_iocb **plug)
 {
 	/*
 	 * If the folio is dirty, only perform writeback if that write
@@ -1201,6 +1202,7 @@  static pageout_t pageout(struct folio *folio, struct address_space *mapping)
 			.range_start = 0,
 			.range_end = LLONG_MAX,
 			.for_reclaim = 1,
+			.swap_plug = plug,
 		};
 
 		folio_set_reclaim(folio);
@@ -1533,6 +1535,7 @@  static unsigned int shrink_page_list(struct list_head *page_list,
 	unsigned int nr_reclaimed = 0;
 	unsigned int pgactivate = 0;
 	bool do_demote_pass;
+	struct swap_iocb *plug = NULL;
 
 	memset(stat, 0, sizeof(*stat));
 	cond_resched();
@@ -1814,7 +1817,7 @@  static unsigned int shrink_page_list(struct list_head *page_list,
 			 * starts and then write it out here.
 			 */
 			try_to_unmap_flush_dirty();
-			switch (pageout(folio, mapping)) {
+			switch (pageout(folio, mapping, &plug)) {
 			case PAGE_KEEP:
 				goto keep_locked;
 			case PAGE_ACTIVATE:
@@ -1968,6 +1971,8 @@  static unsigned int shrink_page_list(struct list_head *page_list,
 	list_splice(&ret_pages, page_list);
 	count_vm_events(PGACTIVATE, pgactivate);
 
+	if (plug)
+		swap_write_unplug(plug);
 	return nr_reclaimed;
 }