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Subject[PATCH 04/13] blk: introduce REQ_SWAP
Date
From: Josef Bacik <jbacik@fb.com>

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 <jbacik@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
include/linux/blk-cgroup.h | 2 +-
include/linux/blk_types.h | 3 ++-
mm/page_io.c | 2 +-
3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index b41292726c0f..a8f9ba8f33a4 100644
--- 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
index ff181df8c195..4f7ba397d37d 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -327,7 +327,7 @@ enum req_flag_bits {

/* for driver use */
__REQ_DRV,
-
+ __REQ_SWAP, /* swapping request. */
__REQ_NR_BITS, /* stops here */
};

@@ -349,6 +349,7 @@ 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
index b41cf9644585..a552cb37e220 100644
--- 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);
--
2.14.3
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