The patch titled
Subject: mm: shmem: split large entry if the swapin folio is not large
has been added to the -mm mm-unstable branch. Its filename is
mm-shmem-split-large-entry-if-the-swapin-folio-is-not-large.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-split-large-entry-if-the-swapin-folio-is-not-large.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: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm: shmem: split large entry if the swapin folio is not large
Date: Mon, 12 Aug 2024 15:42:09 +0800
Now the swap device can only swap-in order 0 folio, even though a large
folio is swapped out. This requires us to split the large entry
previously saved in the shmem pagecache to support the swap in of small
folios.
Link: https://lkml.kernel.org/r/4a0f12f27c54a62eb4d9ca1265fed3a62531a63e.1723434324.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: Daniel Gomez <da.gomez@xxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 100 insertions(+)
--- a/mm/shmem.c~mm-shmem-split-large-entry-if-the-swapin-folio-is-not-large
+++ a/mm/shmem.c
@@ -1986,6 +1986,81 @@ static void shmem_set_folio_swapin_error
swap_free_nr(swap, nr_pages);
}
+static int shmem_split_large_entry(struct inode *inode, pgoff_t index,
+ swp_entry_t swap, int new_order, gfp_t gfp)
+{
+ struct address_space *mapping = inode->i_mapping;
+ XA_STATE_ORDER(xas, &mapping->i_pages, index, new_order);
+ void *alloced_shadow = NULL;
+ int alloced_order = 0, i;
+
+ for (;;) {
+ int order = -1, split_order = 0;
+ void *old = NULL;
+
+ xas_lock_irq(&xas);
+ old = xas_load(&xas);
+ if (!xa_is_value(old) || swp_to_radix_entry(swap) != old) {
+ xas_set_err(&xas, -EEXIST);
+ goto unlock;
+ }
+
+ 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;
+ }
+
+ /* Try to split large swap entry in pagecache */
+ if (order > 0 && order > new_order) {
+ if (!alloced_order) {
+ split_order = order;
+ 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 += (1 << new_order)) {
+ pgoff_t aligned_index = round_down(index, 1 << order);
+ swp_entry_t tmp;
+
+ tmp = swp_entry(swp_type(swap), swp_offset(swap) + i);
+ __xa_store(&mapping->i_pages, aligned_index + i,
+ swp_to_radix_entry(tmp), 0);
+ }
+ }
+
+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;
+}
+
/*
* Swap in the folio pointed to by *foliop.
* Caller has to make sure that *foliop contains a valid swapped folio.
@@ -2022,12 +2097,37 @@ static int shmem_swapin_folio(struct ino
/* Look it up and read it in.. */
folio = swap_cache_get_folio(swap, NULL, 0);
if (!folio) {
+ int split_order;
+
/* Or update major stats only when swapin succeeds?? */
if (fault_type) {
*fault_type |= VM_FAULT_MAJOR;
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(fault_mm, PGMAJFAULT);
}
+
+ /*
+ * Now swap device can only swap in order 0 folio, then we
+ * should split the large swap entry stored in the pagecache
+ * if necessary.
+ */
+ split_order = shmem_split_large_entry(inode, index, swap, 0, gfp);
+ if (split_order < 0) {
+ 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);
+ }
+
/* Here we actually start the io */
folio = shmem_swapin_cluster(swap, gfp, info, index);
if (!folio) {
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-shmem-simplify-the-suitable-huge-orders-validation-for-tmpfs.patch
mm-shmem-rename-shmem_is_huge-to-shmem_huge_global_enabled.patch
mm-shmem-move-shmem_huge_global_enabled-into-shmem_allowable_huge_orders.patch
mm-swap-extend-swap_shmem_alloc-to-support-batch-swap_map_shmem-flag-setting.patch
mm-shmem-extend-shmem_partial_swap_usage-to-support-large-folio-swap.patch
mm-filemap-use-xa_get_order-to-get-the-swap-entry-order.patch
mm-shmem-use-swap_free_nr-to-free-shmem-swap-entries.patch
mm-shmem-support-large-folio-allocation-for-shmem_replace_folio.patch
mm-shmem-drop-folio-reference-count-using-nr_pages-in-shmem_delete_from_page_cache.patch
mm-shmem-split-large-entry-if-the-swapin-folio-is-not-large.patch
mm-shmem-support-large-folio-swap-out.patch
