+ mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/shmem, swap: avoid redundant Xarray lookup during swapin
has been added to the -mm mm-new branch.  Its filename is
     mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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patches, and acceptance into mm-new is a notification for others take
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------------------------------------------------------
From: Kairui Song <kasong@tencent.com>
Subject: mm/shmem, swap: avoid redundant Xarray lookup during swapin
Date: Fri, 27 Jun 2025 14:20:15 +0800

Currently shmem calls xa_get_order to get the swap radix entry order,
requiring a full tree walk.  This can be easily combined with the swap
entry value checking (shmem_confirm_swap) to avoid the duplicated lookup,
which should improve the performance.

Link: https://lkml.kernel.org/r/20250627062020.534-3-ryncsn@gmail.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |   33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

--- a/mm/shmem.c~mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin
+++ a/mm/shmem.c
@@ -505,15 +505,27 @@ static int shmem_replace_entry(struct ad
 
 /*
  * Sometimes, before we decide whether to proceed or to fail, we must check
- * that an entry was not already brought back from swap by a racing thread.
+ * that an entry was not already brought back or split by a racing thread.
  *
  * Checking folio is not enough: by the time a swapcache folio is locked, it
  * might be reused, and again be swapcache, using the same swap as before.
+ * Returns the swap entry's order if it still presents, else returns -1.
  */
-static bool shmem_confirm_swap(struct address_space *mapping,
-			       pgoff_t index, swp_entry_t swap)
+static int shmem_confirm_swap(struct address_space *mapping, pgoff_t index,
+			      swp_entry_t swap)
 {
-	return xa_load(&mapping->i_pages, index) == swp_to_radix_entry(swap);
+	XA_STATE(xas, &mapping->i_pages, index);
+	int ret = -1;
+	void *entry;
+
+	rcu_read_lock();
+	do {
+		entry = xas_load(&xas);
+		if (entry == swp_to_radix_entry(swap))
+			ret = xas_get_order(&xas);
+	} while (xas_retry(&xas, entry));
+	rcu_read_unlock();
+	return ret;
 }
 
 /*
@@ -2256,16 +2268,20 @@ static int shmem_swapin_folio(struct ino
 		return -EIO;
 
 	si = get_swap_device(swap);
-	if (!si) {
-		if (!shmem_confirm_swap(mapping, index, swap))
+	order = shmem_confirm_swap(mapping, index, swap);
+	if (unlikely(!si)) {
+		if (order < 0)
 			return -EEXIST;
 		else
 			return -EINVAL;
 	}
+	if (unlikely(order < 0)) {
+		put_swap_device(si);
+		return -EEXIST;
+	}
 
 	/* Look it up and read it in.. */
 	folio = swap_cache_get_folio(swap, NULL, 0);
-	order = xa_get_order(&mapping->i_pages, index);
 	if (!folio) {
 		int nr_pages = 1 << order;
 		bool fallback_order0 = false;
@@ -2415,7 +2431,7 @@ alloced:
 	*foliop = folio;
 	return 0;
 failed:
-	if (!shmem_confirm_swap(mapping, index, swap))
+	if (shmem_confirm_swap(mapping, index, swap) < 0)
 		error = -EEXIST;
 	if (error == -EIO)
 		shmem_set_folio_swapin_error(inode, index, folio, swap,
@@ -2428,7 +2444,6 @@ unlock:
 		folio_put(folio);
 	}
 	put_swap_device(si);
-
 	return error;
 }
 
_

Patches currently in -mm which might be from kasong@tencent.com are

mm-list_lru-refactor-the-locking-code.patch
mm-shmem-swap-improve-cached-mthp-handling-and-fix-potential-hung.patch
mm-shmem-swap-avoid-redundant-xarray-lookup-during-swapin.patch
mm-shmem-swap-tidy-up-thp-swapin-checks.patch
mm-shmem-swap-clean-up-swap-entry-splitting.patch
mm-shmem-swap-never-use-swap-cache-and-readahead-for-swp_synchronous_io.patch
mm-shmem-swap-fix-major-fault-counting.patch
mm-shmem-swap-avoid-false-positive-swap-cache-lookup.patch