The patch titled
Subject: mm/shmem: use xas_try_split() in shmem_split_large_entry()
has been added to the -mm mm-unstable branch. Its filename is
mm-shmem-use-xas_try_split-in-shmem_split_large_entry.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-use-xas_try_split-in-shmem_split_large_entry.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Zi Yan <ziy@xxxxxxxxxx>
Subject: mm/shmem: use xas_try_split() in shmem_split_large_entry()
Date: Wed, 26 Feb 2025 16:08:54 -0500
During shmem_split_large_entry(), large swap entries are covering n slots
and an order-0 folio needs to be inserted.
Instead of splitting all n slots, only the 1 slot covered by the folio
need to be split and the remaining n-1 shadow entries can be retained with
orders ranging from 0 to n-1. This method only requires
(n/XA_CHUNK_SHIFT) new xa_nodes instead of (n % XA_CHUNK_SHIFT) *
(n/XA_CHUNK_SHIFT) new xa_nodes, compared to the original
xas_split_alloc() + xas_split() one.
For example, to split an order-9 large swap entry (assuming XA_CHUNK_SHIFT
is 6), 1 xa_node is needed instead of 8.
xas_try_split_min_order() is used to reduce the number of calls to
xas_try_split() during split.
Link: https://lkml.kernel.org/r/20250226210854.2045816-3-ziy@xxxxxxxxxx
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Mattew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Kirill A. Shuemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 59 ++++++++++++++++++++++++---------------------------
1 file changed, 28 insertions(+), 31 deletions(-)
--- a/mm/shmem.c~mm-shmem-use-xas_try_split-in-shmem_split_large_entry
+++ a/mm/shmem.c
@@ -2162,15 +2162,16 @@ static int shmem_split_large_entry(struc
{
struct address_space *mapping = inode->i_mapping;
XA_STATE_ORDER(xas, &mapping->i_pages, index, 0);
- void *alloced_shadow = NULL;
- int alloced_order = 0, i;
+ int split_order = 0, entry_order;
+ int i;
/* Convert user data gfp flags to xarray node gfp flags */
gfp &= GFP_RECLAIM_MASK;
for (;;) {
- int order = -1, split_order = 0;
void *old = NULL;
+ int cur_order;
+ pgoff_t swap_index;
xas_lock_irq(&xas);
old = xas_load(&xas);
@@ -2179,60 +2180,56 @@ static int shmem_split_large_entry(struc
goto unlock;
}
- order = xas_get_order(&xas);
+ entry_order = xas_get_order(&xas);
- /* Swap entry may have changed before we re-acquire the lock */
- if (alloced_order &&
- (old != alloced_shadow || order != alloced_order)) {
- xas_destroy(&xas);
- alloced_order = 0;
- }
+ if (!entry_order)
+ goto unlock;
/* Try to split large swap entry in pagecache */
- if (order > 0) {
- if (!alloced_order) {
- split_order = order;
+ cur_order = entry_order;
+ swap_index = round_down(index, 1 << entry_order);
+
+ split_order = xas_try_split_min_order(cur_order);
+
+ while (cur_order > 0) {
+ pgoff_t aligned_index =
+ round_down(index, 1 << cur_order);
+ pgoff_t swap_offset = aligned_index - swap_index;
+
+ xas_set_order(&xas, index, split_order);
+ xas_try_split(&xas, old, cur_order);
+ if (xas_error(&xas))
goto unlock;
- }
- xas_split(&xas, old, order);
/*
* Re-set the swap entry after splitting, and the swap
* offset of the original large entry must be continuous.
*/
- for (i = 0; i < 1 << order; i++) {
- pgoff_t aligned_index = round_down(index, 1 << order);
+ for (i = 0; i < 1 << cur_order;
+ i += (1 << split_order)) {
swp_entry_t tmp;
- tmp = swp_entry(swp_type(swap), swp_offset(swap) + i);
+ tmp = swp_entry(swp_type(swap),
+ swp_offset(swap) + swap_offset +
+ i);
__xa_store(&mapping->i_pages, aligned_index + i,
swp_to_radix_entry(tmp), 0);
}
+ cur_order = split_order;
+ split_order = xas_try_split_min_order(split_order);
}
unlock:
xas_unlock_irq(&xas);
- /* split needed, alloc here and retry. */
- if (split_order) {
- xas_split_alloc(&xas, old, split_order, gfp);
- if (xas_error(&xas))
- goto error;
- alloced_shadow = old;
- alloced_order = split_order;
- xas_reset(&xas);
- continue;
- }
-
if (!xas_nomem(&xas, gfp))
break;
}
-error:
if (xas_error(&xas))
return xas_error(&xas);
- return alloced_order;
+ return entry_order;
}
/*
_
Patches currently in -mm which might be from ziy@xxxxxxxxxx are
selftests-mm-make-file-backed-thp-split-work-by-writing-pmd-size-data.patch
mm-huge_memory-allow-split-shmem-large-folio-to-any-lower-order.patch
selftests-mm-test-splitting-file-backed-thp-to-any-lower-order.patch
xarray-add-xas_try_split-to-split-a-multi-index-entry.patch
mm-huge_memory-add-two-new-not-yet-used-functions-for-folio_split.patch
mm-huge_memory-move-folio-split-common-code-to-__folio_split.patch
mm-huge_memory-add-buddy-allocator-like-non-uniform-folio_split.patch
mm-huge_memory-remove-the-old-unused-__split_huge_page.patch
mm-huge_memory-add-folio_split-to-debugfs-testing-interface.patch
mm-truncate-use-buddy-allocator-like-folio-split-for-truncate-operation.patch
selftests-mm-add-tests-for-folio_split-buddy-allocator-like-split.patch
mm-filemap-use-xas_try_split-in-__filemap_add_folio.patch
mm-shmem-use-xas_try_split-in-shmem_split_large_entry.patch
