__swap_cache_alloc() calls workingset_refault() on every folio it allocates into the swap cache. That is correct for a swap-in, but wrong for a zswap writeback buffer, which is allocated through the same path (swap_cache_alloc_folio()): the buffer is not a refault of anything, yet it gets counted as one, inflating anon refault/activation. Refaulting is a swap-in event, not an allocation event: move it out of __swap_cache_alloc() into the swap-in callers. The allocator has already put the folio on the LRU by the time the callers refault, so workingset_refault() now has to activate an already-LRU folio: folio_set_active() only sets the flag before LRU insertion and would be a no-op here, so use folio_activate() when the folio is already on the LRU. Existing callers pass not-yet-LRU folios and are unaffected. Fixes: aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU") Signed-off-by: Nhat Pham Signed-off-by: Alexandre Ghiti --- mm/swap_state.c | 20 ++++++++++++++++++-- mm/workingset.c | 5 ++++- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index 9c3a5cf99778..0bb26d2ba2ba 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -477,8 +477,6 @@ static struct folio *__swap_cache_alloc(struct swap_cluster_info *ci, /* memsw uncharges swap when folio is added to swap cache */ memcg1_swapin(folio); - if (shadow) - workingset_refault(folio, shadow); node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages); lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages); @@ -638,17 +636,26 @@ static struct folio *swap_cache_read_folio(swp_entry_t entry, gfp_t gfp, struct swap_iocb **plug, bool readahead) { struct folio *folio; + void *shadow = NULL; do { folio = swap_cache_get_folio(entry); if (folio) return folio; + /* + * Capture the slot's shadow before the allocation overwrites it, + * so a fresh swap-in can be evaluated as a refault below. + */ + shadow = swap_cache_get_shadow(entry); folio = swap_cache_alloc_folio(entry, gfp, BIT(0), NULL, mpol, ilx); } while (PTR_ERR(folio) == -EEXIST); if (IS_ERR_OR_NULL(folio)) return NULL; + if (shadow) + workingset_refault(folio, shadow); + swap_read_folio(folio, plug); if (readahead) { folio_set_readahead(folio); @@ -678,17 +685,26 @@ struct folio *swapin_sync(swp_entry_t entry, gfp_t gfp, unsigned long orders, struct vm_fault *vmf, struct mempolicy *mpol, pgoff_t ilx) { struct folio *folio; + void *shadow = NULL; do { folio = swap_cache_get_folio(entry); if (folio) return folio; + /* + * Capture the slot's shadow before the allocation overwrites it, + * so a fresh swap-in can be evaluated as a refault below. + */ + shadow = swap_cache_get_shadow(entry); folio = swap_cache_alloc_folio(entry, gfp, orders, vmf, mpol, ilx); } while (PTR_ERR(folio) == -EEXIST); if (IS_ERR(folio)) return folio; + if (shadow) + workingset_refault(folio, shadow); + swap_read_folio(folio, NULL); return folio; } diff --git a/mm/workingset.c b/mm/workingset.c index f351798e723a..7c30cf091cbf 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -577,7 +577,10 @@ void workingset_refault(struct folio *folio, void *shadow) if (!workingset_test_recent(shadow, file, &workingset, true)) goto out; - folio_set_active(folio); + if (unlikely(folio_test_lru(folio))) + folio_activate(folio); + else + folio_set_active(folio); workingset_age_nonresident(lruvec, nr); mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr); -- 2.53.0-Meta When zswap writes an entry back, allocating the buffer folio in the swap cache overwrites the swap slot's workingset shadow. It is lost and later re-minted inaccurately, which corrupts anon refault/workingset accounting for the written-back data. Preserve it within zswap itself: at writeback, park the shadow in the zswap tree in place of the freed entry, so it outlives the writeback buffer folio. The buffer then meets one of three fates, and the parked shadow is handled at whichever happens first: - swap-in: do_swap_page()/shmem_swapin_folio() find the buffer in the swap cache, take the shadow and feed it to workingset_refault() to account the refault of the now-resident folio, then drop it. - reclaim: __remove_mapping() skips minting a fresh shadow for the buffer (minting would double-count the eviction) and __swap_cache_do_del_folio() restores the parked shadow into the slot, so a later disk swap-in still refaults against the original eviction. - slot free (e.g. process exit): the shadow is not needed and is cleared. The last two both go through __swap_cache_do_del_folio(), the single point every swap-cache removal passes through, which is why the shadow is read and cleared there. Fixes: aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU") Signed-off-by: Nhat Pham Signed-off-by: Alexandre Ghiti --- include/linux/zswap.h | 12 +++++++ mm/memory.c | 5 +++ mm/shmem.c | 5 +++ mm/swap_state.c | 10 ++++++ mm/vmscan.c | 4 ++- mm/zswap.c | 80 ++++++++++++++++++++++++++++++++++++++++++- 6 files changed, 114 insertions(+), 2 deletions(-) diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 30c193a1207e..dfb7153236f5 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -35,6 +35,8 @@ void zswap_lruvec_state_init(struct lruvec *lruvec); void zswap_folio_swapin(struct folio *folio); bool zswap_is_enabled(void); bool zswap_never_enabled(void); +bool zswap_folio_is_writeback_buffer(struct folio *folio); +void *zswap_lookup_and_clear_shadows(struct folio *folio); #else struct zswap_lruvec_state {}; @@ -69,6 +71,16 @@ static inline bool zswap_never_enabled(void) return true; } +static inline bool zswap_folio_is_writeback_buffer(struct folio *folio) +{ + return false; +} + +static inline void *zswap_lookup_and_clear_shadows(struct folio *folio) +{ + return NULL; +} + #endif #endif /* _LINUX_ZSWAP_H */ diff --git a/mm/memory.c b/mm/memory.c index 56be920c56d7..ebc332761c2c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4759,6 +4759,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) unsigned long page_idx; unsigned long address; pte_t *ptep; + void *shadow; if (!pte_unmap_same(vmf)) goto out; @@ -4880,6 +4881,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) goto out_page; } + shadow = zswap_lookup_and_clear_shadows(folio); + if (shadow) + workingset_refault(folio, shadow); + /* * KSM sometimes has to copy on read faults, for example, if * folio->index of non-ksm folios would be nonlinear inside the diff --git a/mm/shmem.c b/mm/shmem.c index 56c23a7b15c7..3ac9abc7ba8e 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2242,6 +2242,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, struct folio *folio = NULL; int error, nr_pages, order; pgoff_t offset; + void *shadow; VM_BUG_ON(!*foliop || !xa_is_value(*foliop)); index_entry = radix_to_swp_entry(*foliop); @@ -2353,6 +2354,10 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, */ arch_swap_restore(folio_swap(swap, folio), folio); + shadow = zswap_lookup_and_clear_shadows(folio); + if (shadow) + workingset_refault(folio, shadow); + if (shmem_should_replace_folio(folio, gfp)) { error = shmem_replace_folio(&folio, gfp, info, index, vma); if (error) diff --git a/mm/swap_state.c b/mm/swap_state.c index 0bb26d2ba2ba..7ea4a2ba0841 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -22,6 +22,7 @@ #include #include #include +#include #include "internal.h" #include "swap_table.h" #include "swap.h" @@ -257,12 +258,21 @@ static void __swap_cache_do_del_folio(struct swap_cluster_info *ci, unsigned int ci_start, ci_off, ci_end; bool folio_swapped = false, need_free = false; unsigned long nr_pages = folio_nr_pages(folio); + void *shadow_parked; VM_WARN_ON_ONCE(__swap_entry_to_cluster(entry) != ci); VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio); VM_WARN_ON_ONCE_FOLIO(folio_test_writeback(folio), folio); + /* + * A zswap writeback buffer parked the slot's original shadow in the + * zswap tree: restore it into the slot for later swap-in. + */ + shadow_parked = zswap_lookup_and_clear_shadows(folio); + if (shadow_parked) + shadow = shadow_parked; + si = __swap_entry_to_info(entry); ci_start = swp_cluster_offset(entry); ci_end = ci_start + nr_pages; diff --git a/mm/vmscan.c b/mm/vmscan.c index 3f3ff25e561a..2c57e88421b0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -48,6 +48,7 @@ #include #include #include +#include #include #include #include @@ -735,7 +736,8 @@ static int __remove_mapping(struct address_space *mapping, struct folio *folio, if (folio_test_swapcache(folio)) { swp_entry_t swap = folio->swap; - if (reclaimed && !mapping_exiting(mapping)) + if (reclaimed && !mapping_exiting(mapping) && + !zswap_folio_is_writeback_buffer(folio)) shadow = workingset_eviction(folio, target_memcg); __memcg1_swapout(folio, ci); __swap_cache_del_folio(ci, folio, swap, shadow); diff --git a/mm/zswap.c b/mm/zswap.c index 761cd699e0a3..f059206948ab 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -972,6 +972,79 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio) /********************************* * writeback code **********************************/ + +#define ZSWAP_WRITEBACK_NO_SHADOW xa_mk_value(0) + +/* + * zswap_folio_is_writeback_buffer - is @folio a zswap writeback buffer? + * @folio: the folio being examined (typically a swap cache folio under reclaim) + * + * A folio is a zswap writeback buffer when every one of its swap offsets holds + * a parked writeback shadow (a real shadow or the ZSWAP_WRITEBACK_NO_SHADOW + * sentinel) in the zswap tree rather than a live zswap entry. + * + * Return: true if @folio is a writeback buffer, in which case the reclaim path + * must not mint a fresh workingset shadow for it. + */ +bool zswap_folio_is_writeback_buffer(struct folio *folio) +{ + swp_entry_t swp = folio->swap; + unsigned long nr_pages = folio_nr_pages(folio); + pgoff_t offset = swp_offset(swp); + unsigned long i; + + if (zswap_never_enabled()) + return false; + + for (i = 0; i < nr_pages; i++) { + swp_entry_t e = swp_entry(swp_type(swp), offset + i); + + if (!xa_is_value(xa_load(swap_zswap_tree(e), offset + i))) + return false; + } + + return true; +} + +/* + * zswap_lookup_and_clear_shadows - retrieve and clear @folio's parked shadow(s) + * @folio: the writeback buffer folio (or the swapin folio that consumed it) + * + * Remove any parked writeback shadows for @folio's swap offset(s) from the + * zswap tree. + * + * Return: the preserved workingset shadow, or NULL if the slot(s) had no shadow + * (sentinel only) or nothing parked. The caller either restores the returned + * shadow into the swap slot (buffer dropped) or feeds it to workingset_refault() + * (buffer consumed by a swapin); clearing here ensures the two paths never + * double-count. + */ +void *zswap_lookup_and_clear_shadows(struct folio *folio) +{ + swp_entry_t swp = folio->swap; + unsigned long nr_pages = folio_nr_pages(folio); + pgoff_t offset = swp_offset(swp); + void *shadow = NULL; + unsigned long i; + + if (zswap_never_enabled()) + return NULL; + + for (i = 0; i < nr_pages; i++) { + swp_entry_t e = swp_entry(swp_type(swp), offset + i); + struct xarray *tree = swap_zswap_tree(e); + void *parked = xa_load(tree, offset + i); + + if (!xa_is_value(parked)) + continue; + xa_erase(tree, offset + i); + if (parked != ZSWAP_WRITEBACK_NO_SHADOW) + shadow = parked; + } + + return shadow; +} + /* * Attempts to free an entry by adding a folio to the swap cache, * decompressing the entry data into the folio, and issuing a @@ -992,6 +1065,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, struct folio *folio; struct mempolicy *mpol; struct swap_info_struct *si; + void *shadow; int ret = 0; /* try to allocate swap cache folio */ @@ -999,6 +1073,8 @@ static int zswap_writeback_entry(struct zswap_entry *entry, if (!si) return -EEXIST; + shadow = swap_cache_get_shadow(swpentry); + mpol = get_task_policy(current); folio = swap_cache_alloc_folio(swpentry, GFP_KERNEL, BIT(0), NULL, mpol, NO_INTERLEAVE_INDEX); @@ -1034,7 +1110,9 @@ static int zswap_writeback_entry(struct zswap_entry *entry, goto out; } - xa_erase(tree, offset); + if (!shadow) + shadow = ZSWAP_WRITEBACK_NO_SHADOW; + xa_store(tree, offset, shadow, GFP_KERNEL); count_vm_event(ZSWPWB); if (entry->objcg) -- 2.53.0-Meta