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Message-ID: <20250514201729.48420-14-ryncsn@gmail.com>
Date: Thu, 15 May 2025 04:17:13 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Hugh Dickins <hughd@...gle.com>,
Chris Li <chrisl@...nel.org>,
David Hildenbrand <david@...hat.com>,
Yosry Ahmed <yosryahmed@...gle.com>,
"Huang, Ying" <ying.huang@...ux.alibaba.com>,
Nhat Pham <nphamcs@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Baoquan He <bhe@...hat.com>,
Barry Song <baohua@...nel.org>,
Kalesh Singh <kaleshsingh@...gle.com>,
Kemeng Shi <shikemeng@...weicloud.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Ryan Roberts <ryan.roberts@....com>,
linux-kernel@...r.kernel.org,
Kairui Song <kasong@...cent.com>
Subject: [PATCH 13/28] mm/shmem, swap: avoid redundant Xarray lookup during swapin
From: Kairui Song <kasong@...cent.com>
Currently shmem calls xa_get_order multiple times to get the swap radix
entry order. This can be combined with the swap entry value checking
(shmem_confirm_swap) to avoid the duplicated lookup, which should
improve the performance.
This also provides the helper need for later commits.
Signed-off-by: Kairui Song <kasong@...cent.com>
---
mm/shmem.c | 67 ++++++++++++++++++++++++++++++------------------------
1 file changed, 37 insertions(+), 30 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 0da9e06eaee8..da80a8faa39e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -509,11 +509,26 @@ static int shmem_replace_entry(struct address_space *mapping,
*
* 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.
+ *
+ * Check if the swap entry is still in the shmem mapping and get its order,
+ * return -1 if it's no longer valid.
*/
-static bool shmem_confirm_swap(struct address_space *mapping,
- pgoff_t index, swp_entry_t swap)
+static int shmem_check_swap_entry(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 order = -1;
+ void *entry;
+
+ rcu_read_lock();
+ do {
+ entry = xas_load(&xas);
+ if (entry == swp_to_radix_entry(swap))
+ order = xas_get_order(&xas);
+ } while (xas_retry(&xas, entry));
+ rcu_read_unlock();
+
+ return order;
}
/*
@@ -2238,16 +2253,17 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
return -EIO;
si = get_swap_device(swap);
- if (!si) {
- if (!shmem_confirm_swap(mapping, index, swap))
- return -EEXIST;
- else
- return -EINVAL;
+ order = shmem_check_swap_entry(mapping, index, swap);
+ if (order < 0) {
+ if (si)
+ put_swap_device(si);
+ return -EEXIST;
}
+ if (!si)
+ return -EINVAL;
/* Look it up and read it in.. */
folio = swap_cache_get_folio(swap);
- order = xa_get_order(&mapping->i_pages, index);
if (!folio) {
bool fallback_order0 = false;
@@ -2303,7 +2319,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
*/
if (split_order > 0) {
pgoff_t offset = index - round_down(index, 1 << split_order);
-
swap = swp_entry(swp_type(swap), swp_offset(swap) + offset);
}
@@ -2325,25 +2340,20 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
error = split_order;
goto failed;
}
-
- /*
- * If the large swap entry has already been split, it is
- * necessary to recalculate the new swap entry based on
- * the old order alignment.
- */
- if (split_order > 0) {
- pgoff_t offset = index - round_down(index, 1 << split_order);
-
- swap = swp_entry(swp_type(swap), swp_offset(swap) + offset);
- }
}
alloced:
/* We have to do this with folio locked to prevent races */
folio_lock(folio);
- if ((!skip_swapcache && !folio_test_swapcache(folio)) ||
- folio->swap.val != swap.val ||
- !shmem_confirm_swap(mapping, index, swap) ||
- xa_get_order(&mapping->i_pages, index) != folio_order(folio)) {
+ if (!skip_swapcache && !folio_swap_contains(folio, swap)) {
+ error = -EEXIST;
+ goto unlock;
+ }
+
+ nr_pages = folio_nr_pages(folio);
+ index = round_down(index, nr_pages);
+ swap = swp_entry(swp_type(swap), round_down(swp_offset(swap), nr_pages));
+
+ if (folio_order(folio) != shmem_check_swap_entry(mapping, index, swap)) {
error = -EEXIST;
goto unlock;
}
@@ -2354,7 +2364,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
goto failed;
}
folio_wait_writeback(folio);
- nr_pages = folio_nr_pages(folio);
/*
* Some architectures may have to restore extra metadata to the
@@ -2368,8 +2377,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
goto failed;
}
- error = shmem_add_to_page_cache(folio, mapping,
- round_down(index, nr_pages),
+ error = shmem_add_to_page_cache(folio, mapping, index,
swp_to_radix_entry(swap), gfp);
if (error)
goto failed;
@@ -2392,7 +2400,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
*foliop = folio;
return 0;
failed:
- if (!shmem_confirm_swap(mapping, index, swap))
+ if (shmem_check_swap_entry(mapping, index, swap) < 0)
error = -EEXIST;
if (error == -EIO)
shmem_set_folio_swapin_error(inode, index, folio, swap,
@@ -2405,7 +2413,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
folio_put(folio);
}
put_swap_device(si);
-
return error;
}
--
2.49.0
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