From 12885cbe88ddf6c5fc3306193a6449ac310f2331 Mon Sep 17 00:00:00 2001 From: Baolin Wang Date: Mon, 12 Aug 2024 15:42:09 +0800 Subject: [PATCH] mm: shmem: split large entry if the swapin folio is not large 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. [hughd@google.com: fix warnings from kmalloc_fix_flags()] Link: https://lkml.kernel.org/r/e2a2ba5d-864c-50aa-7579-97cba1c7dd0c@google.com [baolin.wang@linux.alibaba.com: drop the 'new_order' parameter] Link: https://lkml.kernel.org/r/39c71ccf-669b-4d9f-923c-f6b9c4ceb8df@linux.alibaba.com Link: https://lkml.kernel.org/r/4a0f12f27c54a62eb4d9ca1265fed3a62531a63e.1723434324.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Signed-off-by: Hugh Dickins Cc: Barry Song Cc: Chris Li Cc: Daniel Gomez Cc: David Hildenbrand Cc: "Huang, Ying" Cc: Kefeng Wang Cc: Lance Yang Cc: Matthew Wilcox Cc: Pankaj Raghav Cc: Ryan Roberts Cc: Yang Shi Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/shmem.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 103 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 598d003b7a89..4af6f3ea9c4f 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1999,6 +1999,84 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index, swap_free_nr(swap, nr_pages); } +static int shmem_split_large_entry(struct inode *inode, pgoff_t index, + swp_entry_t swap, gfp_t gfp) +{ + 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; + + /* Convert user data gfp flags to xarray node gfp flags */ + gfp &= GFP_RECLAIM_MASK; + + 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) { + 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++) { + 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. @@ -2036,12 +2114,37 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, /* 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, 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) { -- 2.50.1