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Subject[PATCH v4 3/6] mm: introduce pte_move_swp_offset() helper which can move offset bidirectionally
Date
From: Barry Song <v-songbaohua@oppo.com>

There could arise a necessity to obtain the first pte_t from a swap
pte_t located in the middle. For instance, this may occur within the
context of do_swap_page(), where a page fault can potentially occur in
any PTE of a large folio. To address this, the following patch introduces
pte_move_swp_offset(), a function capable of bidirectional movement by
a specified delta argument. Consequently, pte_next_swp_offset()
will directly invoke it with delta = 1.

Suggested-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
---
mm/internal.h | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index b2c75b12014e..17b0a1824948 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -211,18 +211,21 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr,
}

/**
- * pte_next_swp_offset - Increment the swap entry offset field of a swap pte.
+ * pte_move_swp_offset - Move the swap entry offset field of a swap pte
+ * forward or backward by delta
* @pte: The initial pte state; is_swap_pte(pte) must be true and
* non_swap_entry() must be false.
+ * @delta: The direction and the offset we are moving; forward if delta
+ * is positive; backward if delta is negative
*
- * Increments the swap offset, while maintaining all other fields, including
+ * Moves the swap offset, while maintaining all other fields, including
* swap type, and any swp pte bits. The resulting pte is returned.
*/
-static inline pte_t pte_next_swp_offset(pte_t pte)
+static inline pte_t pte_move_swp_offset(pte_t pte, long delta)
{
swp_entry_t entry = pte_to_swp_entry(pte);
pte_t new = __swp_entry_to_pte(__swp_entry(swp_type(entry),
- (swp_offset(entry) + 1)));
+ (swp_offset(entry) + delta)));

if (pte_swp_soft_dirty(pte))
new = pte_swp_mksoft_dirty(new);
@@ -234,6 +237,20 @@ static inline pte_t pte_next_swp_offset(pte_t pte)
return new;
}

+
+/**
+ * pte_next_swp_offset - Increment the swap entry offset field of a swap pte.
+ * @pte: The initial pte state; is_swap_pte(pte) must be true and
+ * non_swap_entry() must be false.
+ *
+ * Increments the swap offset, while maintaining all other fields, including
+ * swap type, and any swp pte bits. The resulting pte is returned.
+ */
+static inline pte_t pte_next_swp_offset(pte_t pte)
+{
+ return pte_move_swp_offset(pte, 1);
+}
+
/**
* swap_pte_batch - detect a PTE batch for a set of contiguous swap entries
* @start_ptep: Page table pointer for the first entry.
--
2.34.1

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