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mm/page-writeback: introduce tracepoint for wait_on_page_writeback()
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Recently there have been some hung tasks on our server due to
wait_on_page_writeback(), and we want to know the details of this
PG_writeback, i.e.  this page is writing back to which device.  But it is
not so convenient to get the details.

I think it would be better to introduce a tracepoint for diagnosing the
writeback details.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yafang Shao <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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laoar authored and torvalds committed May 14, 2019
1 parent 60b62ff commit 19343b5
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Showing 3 changed files with 28 additions and 10 deletions.
10 changes: 1 addition & 9 deletions include/linux/pagemap.h
Original file line number Diff line number Diff line change
Expand Up @@ -540,15 +540,7 @@ static inline int wait_on_page_locked_killable(struct page *page)

extern void put_and_wait_on_page_locked(struct page *page);

/*
* Wait for a page to complete writeback
*/
static inline void wait_on_page_writeback(struct page *page)
{
if (PageWriteback(page))
wait_on_page_bit(page, PG_writeback);
}

void wait_on_page_writeback(struct page *page);
extern void end_page_writeback(struct page *page);
void wait_for_stable_page(struct page *page);

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16 changes: 15 additions & 1 deletion include/trace/events/writeback.h
Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,7 @@ WB_WORK_REASON

struct wb_writeback_work;

TRACE_EVENT(writeback_dirty_page,
DECLARE_EVENT_CLASS(writeback_page_template,

TP_PROTO(struct page *page, struct address_space *mapping),

Expand All @@ -79,6 +79,20 @@ TRACE_EVENT(writeback_dirty_page,
)
);

DEFINE_EVENT(writeback_page_template, writeback_dirty_page,

TP_PROTO(struct page *page, struct address_space *mapping),

TP_ARGS(page, mapping)
);

DEFINE_EVENT(writeback_page_template, wait_on_page_writeback,

TP_PROTO(struct page *page, struct address_space *mapping),

TP_ARGS(page, mapping)
);

DECLARE_EVENT_CLASS(writeback_dirty_inode_template,

TP_PROTO(struct inode *inode, int flags),
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12 changes: 12 additions & 0 deletions mm/page-writeback.c
Original file line number Diff line number Diff line change
Expand Up @@ -2808,6 +2808,18 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
}
EXPORT_SYMBOL(__test_set_page_writeback);

/*
* Wait for a page to complete writeback
*/
void wait_on_page_writeback(struct page *page)
{
if (PageWriteback(page)) {
trace_wait_on_page_writeback(page, page_mapping(page));
wait_on_page_bit(page, PG_writeback);
}
}
EXPORT_SYMBOL_GPL(wait_on_page_writeback);

/**
* wait_for_stable_page() - wait for writeback to finish, if necessary.
* @page: The page to wait on.
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