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charset="utf-8" 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. Cc: Baolin Wang Cc: Hugh Dickins Cc: Kairui Song Cc: Mattew Wilcox Cc: Miaohe Lin Cc: David Hildenbrand Cc: John Hubbard Cc: Kefeng Wang Cc: Kirill A. Shuemov Cc: Ryan Roberts Cc: Yang Shi Cc: Yu Zhao Reviewed-by: Baolin Wang Tested-by: Baolin Wang Signed-off-by: Zi Yan --- mm/shmem.c | 59 ++++++++++++++++++++++++++---------------------------- 1 file changed, 28 insertions(+), 31 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 5586903950b3..7b738d8d6581 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2153,15 +2153,16 @@ static int shmem_split_large_entry(struct inode *in= ode, pgoff_t index, { struct address_space *mapping =3D inode->i_mapping; XA_STATE_ORDER(xas, &mapping->i_pages, index, 0); - void *alloced_shadow =3D NULL; - int alloced_order =3D 0, i; + int split_order =3D 0, entry_order; + int i; =20 /* Convert user data gfp flags to xarray node gfp flags */ gfp &=3D GFP_RECLAIM_MASK; =20 for (;;) { - int order =3D -1, split_order =3D 0; void *old =3D NULL; + int cur_order; + pgoff_t swap_index; =20 xas_lock_irq(&xas); old =3D xas_load(&xas); @@ -2170,60 +2171,56 @@ static int shmem_split_large_entry(struct inode *in= ode, pgoff_t index, goto unlock; } =20 - order =3D xas_get_order(&xas); + entry_order =3D xas_get_order(&xas); =20 - /* Swap entry may have changed before we re-acquire the lock */ - if (alloced_order && - (old !=3D alloced_shadow || order !=3D alloced_order)) { - xas_destroy(&xas); - alloced_order =3D 0; - } + if (!entry_order) + goto unlock; =20 /* Try to split large swap entry in pagecache */ - if (order > 0) { - if (!alloced_order) { - split_order =3D order; + cur_order =3D entry_order; + swap_index =3D round_down(index, 1 << entry_order); + + split_order =3D xas_try_split_min_order(cur_order); + + while (cur_order > 0) { + pgoff_t aligned_index =3D + round_down(index, 1 << cur_order); + pgoff_t swap_offset =3D 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); =20 /* * Re-set the swap entry after splitting, and the swap * offset of the original large entry must be continuous. */ - for (i =3D 0; i < 1 << order; i++) { - pgoff_t aligned_index =3D round_down(index, 1 << order); + for (i =3D 0; i < 1 << cur_order; + i +=3D (1 << split_order)) { swp_entry_t tmp; =20 - tmp =3D swp_entry(swp_type(swap), swp_offset(swap) + i); + tmp =3D 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 =3D split_order; + split_order =3D xas_try_split_min_order(split_order); } =20 unlock: xas_unlock_irq(&xas); =20 - /* 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 =3D old; - alloced_order =3D split_order; - xas_reset(&xas); - continue; - } - if (!xas_nomem(&xas, gfp)) break; } =20 -error: if (xas_error(&xas)) return xas_error(&xas); =20 - return alloced_order; + return entry_order; } =20 /* --=20 2.47.2