blk: introduce REQ_SWAP

Josef Bacik · axboe · commit 0d1e0c7cd590 · 2018-07-09T09:07:54.000-06:00
Just like REQ_META, it's important to know the IO coming down is swap
in order to guard against potential IO priority inversion issues with
cgroups.  Add REQ_SWAP and use it for all swap IO, and add it to our
bio_issue_as_root_blkg helper.

Signed-off-by: Josef Bacik &lt;jbacik@fb.com&gt;
Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
@@ -254,7 +254,7 @@ static inline struct blkcg *bio_blkcg(struct bio *bio)
  */
 static inline bool bio_issue_as_root_blkg(struct bio *bio)
 {
-	return (bio->bi_opf & REQ_META);
+	return (bio->bi_opf & (REQ_META | REQ_SWAP)) != 0;
 }
 
 /**
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
@@ -329,7 +329,7 @@ enum req_flag_bits {
 
 	/* for driver use */
 	__REQ_DRV,
-
+	__REQ_SWAP,		/* swapping request. */
 	__REQ_NR_BITS,		/* stops here */
 };
 
@@ -351,6 +351,7 @@ enum req_flag_bits {
 #define REQ_NOUNMAP		(1ULL << __REQ_NOUNMAP)
 
 #define REQ_DRV			(1ULL << __REQ_DRV)
+#define REQ_SWAP		(1ULL << __REQ_SWAP)
 
 #define REQ_FAILFAST_MASK \
 	(REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
diff --git a/mm/page_io.c b/mm/page_io.c
@@ -338,7 +338,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
 		ret = -ENOMEM;
 		goto out;
 	}
-	bio->bi_opf = REQ_OP_WRITE | wbc_to_write_flags(wbc);
+	bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
 	count_swpout_vm_event(page);
 	set_page_writeback(page);
 	unlock_page(page);

Original file line number	Diff line number	Diff line change
`@@ -254,7 +254,7 @@ static inline struct blkcg bio_blkcg(struct bio bio)`
`254`	`254`	`*/`
`255`	`255`	`static inline bool bio_issue_as_root_blkg(struct bio *bio)`
`256`	`256`	`{`
`257`		`- return (bio->bi_opf & REQ_META);`
	`257`	`+ return (bio->bi_opf & (REQ_META \| REQ_SWAP)) != 0;`
`258`	`258`	`}`
`259`	`259`
`260`	`260`	`/**`
Original file line number	Diff line number	Diff line change
`@@ -338,7 +338,7 @@ int __swap_writepage(struct page page, struct writeback_control wbc,`
`338`	`338`	`ret = -ENOMEM;`
`339`	`339`	`goto out;`
`340`	`340`	`}`
`341`		`- bio->bi_opf = REQ_OP_WRITE \| wbc_to_write_flags(wbc);`
	`341`	`+ bio->bi_opf = REQ_OP_WRITE \| REQ_SWAP \| wbc_to_write_flags(wbc);`
`342`	`342`	`count_swpout_vm_event(page);`
`343`	`343`	`set_page_writeback(page);`
`344`	`344`	`unlock_page(page);`