linux-kernel - [RFC PATCH 05/79] mm/swap: add an helper to get address_space from swap_entry

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Date:   Wed,  4 Apr 2018 15:17:52 -0400
From:   jglisse@...hat.com
To:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [RFC PATCH 05/79] mm/swap: add an helper to get address_space from swap_entry_t

From: Jérôme Glisse <jglisse@...hat.com>

Each swap entry is associated to a file and thus an address_space.
That address_space is use for reading/writing to swap storage. This
patch add an helper to get the address_space from swap_entry_t.

Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 include/linux/swap.h | 1 +
 mm/swapfile.c        | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index a1a3f4ed94ce..e2155df84d77 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -475,6 +475,7 @@ extern int __swp_swapcount(swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
 extern struct swap_info_struct *page_swap_info(struct page *);
 extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
+struct address_space *swap_entry_to_address_space(swp_entry_t swap);
 extern bool reuse_swap_page(struct page *, int *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index c7a33717d079..a913d4b45866 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3467,6 +3467,13 @@ struct swap_info_struct *swp_swap_info(swp_entry_t entry)
 	return swap_info[swp_type(entry)];
 }
 
+struct address_space *swap_entry_to_address_space(swp_entry_t swap)
+{
+	struct swap_info_struct *sis = swp_swap_info(swap);
+
+	return sis->swap_file->f_mapping;
+}
+
 struct swap_info_struct *page_swap_info(struct page *page)
 {
 	swp_entry_t entry = { .val = page_private(page) };
-- 
2.14.3