The interface of list_lru is based on the assumption that the list node and the data it represents belong to the same allocated on the correct node/memcg. While this assumption is valid for existing slab objects LRU such as dentries and inodes, it is undocumented, and rather inflexible for certain potential list_lru users (such as the upcoming zswap shrinker and the THP shrinker). It has caused us a lot of issues during our development.

This patch changes list_lru interface so that the caller must explicitly specify numa node and memcg when adding and removing objects. The old list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and list_lru_del_obj(), respectively.

It also extends the list_lru API with a new function, list_lru_putback, which undoes a previous list_lru_isolate call. Unlike list_lru_add, it does not increment the LRU node count (as list_lru_isolate does not decrement the node count). list_lru_putback also allows for explicit memcg and NUMA node selection.

Suggested-by: Johannes Weiner hannes@cmpxchg.org Signed-off-by: Nhat Pham nphamcs@gmail.com --- drivers/android/binder_alloc.c | 5 ++-- fs/dcache.c | 8 +++--- fs/gfs2/quota.c | 6 ++--- fs/inode.c | 4 +-- fs/nfs/nfs42xattr.c | 8 +++--- fs/nfsd/filecache.c | 4 +-- fs/xfs/xfs_buf.c | 6 ++--- fs/xfs/xfs_dquot.c | 2 +- fs/xfs/xfs_qm.c | 2 +- include/linux/list_lru.h | 46 +++++++++++++++++++++++++++++--- mm/list_lru.c | 48 ++++++++++++++++++++++++++++------ mm/workingset.c | 4 +-- 12 files changed, 108 insertions(+), 35 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 138f6d43d13b..e80669d4e037 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -285,7 +285,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,

trace_binder_free_lru_start(alloc, index);

- ret = list_lru_add(&binder_alloc_lru, &page->lru); + ret = list_lru_add_obj(&binder_alloc_lru, &page->lru); WARN_ON(!ret);

trace_binder_free_lru_end(alloc, index); @@ -848,7 +848,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc) if (!alloc->pages[i].page_ptr) continue;

- on_lru = list_lru_del(&binder_alloc_lru, + on_lru = list_lru_del_obj(&binder_alloc_lru, &alloc->pages[i].lru); page_addr = alloc->buffer + i * PAGE_SIZE; binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC, @@ -1287,4 +1287,3 @@ int binder_alloc_copy_from_buffer(struct binder_alloc *alloc, return binder_alloc_do_buffer_copy(alloc, false, buffer, buffer_offset, dest, bytes); } - diff --git a/fs/dcache.c b/fs/dcache.c index 25ac74d30bff..482d1b34d88d 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -428,7 +428,8 @@ static void d_lru_add(struct dentry *dentry) this_cpu_inc(nr_dentry_unused); if (d_is_negative(dentry)) this_cpu_inc(nr_dentry_negative); - WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + WARN_ON_ONCE(!list_lru_add_obj( + &dentry->d_sb->s_dentry_lru, &dentry->d_lru)); }

static void d_lru_del(struct dentry *dentry) @@ -438,7 +439,8 @@ static void d_lru_del(struct dentry *dentry) this_cpu_dec(nr_dentry_unused); if (d_is_negative(dentry)) this_cpu_dec(nr_dentry_negative); - WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + WARN_ON_ONCE(!list_lru_del_obj( + &dentry->d_sb->s_dentry_lru, &dentry->d_lru)); }

static void d_shrink_del(struct dentry *dentry) @@ -1240,7 +1242,7 @@ static enum lru_status dentry_lru_isolate(struct list_head *item, * * This is guaranteed by the fact that all LRU management * functions are intermediated by the LRU API calls like - * list_lru_add and list_lru_del. List movement in this file + * list_lru_add_obj and list_lru_del_obj. List movement in this file * only ever occur through this functions or through callbacks * like this one, that are called from the LRU API. * diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c index 2f1328af34f4..72015594bc83 100644 --- a/fs/gfs2/quota.c +++ b/fs/gfs2/quota.c @@ -271,7 +271,7 @@ static struct gfs2_quota_data *gfs2_qd_search_bucket(unsigned int hash, if (qd->qd_sbd != sdp) continue; if (lockref_get_not_dead(&qd->qd_lockref)) { - list_lru_del(&gfs2_qd_lru, &qd->qd_lru); + list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru); return qd; } } @@ -344,7 +344,7 @@ static void qd_put(struct gfs2_quota_data *qd) }

qd->qd_lockref.count = 0; - list_lru_add(&gfs2_qd_lru, &qd->qd_lru); + list_lru_add_obj(&gfs2_qd_lru, &qd->qd_lru); spin_unlock(&qd->qd_lockref.lock); }

@@ -1508,7 +1508,7 @@ void gfs2_quota_cleanup(struct gfs2_sbd *sdp) lockref_mark_dead(&qd->qd_lockref); spin_unlock(&qd->qd_lockref.lock);

- list_lru_del(&gfs2_qd_lru, &qd->qd_lru); + list_lru_del_obj(&gfs2_qd_lru, &qd->qd_lru); list_add(&qd->qd_lru, &dispose); } spin_unlock(&qd_lock); diff --git a/fs/inode.c b/fs/inode.c index 84bc3c76e5cc..f889ba8dccd9 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -462,7 +462,7 @@ static void __inode_add_lru(struct inode *inode, bool rotate) if (!mapping_shrinkable(&inode->i_data)) return;

- if (list_lru_add(&inode->i_sb->s_inode_lru, &inode->i_lru)) + if (list_lru_add_obj(&inode->i_sb->s_inode_lru, &inode->i_lru)) this_cpu_inc(nr_unused); else if (rotate) inode->i_state |= I_REFERENCED; @@ -480,7 +480,7 @@ void inode_add_lru(struct inode *inode)

static void inode_lru_list_del(struct inode *inode) { - if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru)) + if (list_lru_del_obj(&inode->i_sb->s_inode_lru, &inode->i_lru)) this_cpu_dec(nr_unused); }

diff --git a/fs/nfs/nfs42xattr.c b/fs/nfs/nfs42xattr.c index 2ad66a8922f4..49aaf28a6950 100644 --- a/fs/nfs/nfs42xattr.c +++ b/fs/nfs/nfs42xattr.c @@ -132,7 +132,7 @@ nfs4_xattr_entry_lru_add(struct nfs4_xattr_entry *entry) lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ? &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

- return list_lru_add(lru, &entry->lru); + return list_lru_add_obj(lru, &entry->lru); }

static bool @@ -143,7 +143,7 @@ nfs4_xattr_entry_lru_del(struct nfs4_xattr_entry *entry) lru = (entry->flags & NFS4_XATTR_ENTRY_EXTVAL) ? &nfs4_xattr_large_entry_lru : &nfs4_xattr_entry_lru;

- return list_lru_del(lru, &entry->lru); + return list_lru_del_obj(lru, &entry->lru); }

/* @@ -349,7 +349,7 @@ nfs4_xattr_cache_unlink(struct inode *inode)

oldcache = nfsi->xattr_cache; if (oldcache != NULL) { - list_lru_del(&nfs4_xattr_cache_lru, &oldcache->lru); + list_lru_del_obj(&nfs4_xattr_cache_lru, &oldcache->lru); oldcache->inode = NULL; } nfsi->xattr_cache = NULL; @@ -474,7 +474,7 @@ nfs4_xattr_get_cache(struct inode *inode, int add) kref_get(&cache->ref); nfsi->xattr_cache = cache; cache->inode = inode; - list_lru_add(&nfs4_xattr_cache_lru, &cache->lru); + list_lru_add_obj(&nfs4_xattr_cache_lru, &cache->lru); }

spin_unlock(&inode->i_lock); diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index 9c62b4502539..82352c100b49 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -322,7 +322,7 @@ nfsd_file_check_writeback(struct nfsd_file *nf) static bool nfsd_file_lru_add(struct nfsd_file *nf) { set_bit(NFSD_FILE_REFERENCED, &nf->nf_flags); - if (list_lru_add(&nfsd_file_lru, &nf->nf_lru)) { + if (list_lru_add_obj(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_add(nf); return true; } @@ -331,7 +331,7 @@ static bool nfsd_file_lru_add(struct nfsd_file *nf)

static bool nfsd_file_lru_remove(struct nfsd_file *nf) { - if (list_lru_del(&nfsd_file_lru, &nf->nf_lru)) { + if (list_lru_del_obj(&nfsd_file_lru, &nf->nf_lru)) { trace_nfsd_file_lru_del(nf); return true; } diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 9e7ba04572db..9c2654a8d24b 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -169,7 +169,7 @@ xfs_buf_stale(

atomic_set(&bp->b_lru_ref, 0); if (!(bp->b_state & XFS_BSTATE_DISPOSE) && - (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru))) + (list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru))) atomic_dec(&bp->b_hold);

ASSERT(atomic_read(&bp->b_hold) >= 1); @@ -1047,7 +1047,7 @@ xfs_buf_rele( * buffer for the LRU and clear the (now stale) dispose list * state flag */ - if (list_lru_add(&bp->b_target->bt_lru, &bp->b_lru)) { + if (list_lru_add_obj(&bp->b_target->bt_lru, &bp->b_lru)) { bp->b_state &= ~XFS_BSTATE_DISPOSE; atomic_inc(&bp->b_hold); } @@ -1060,7 +1060,7 @@ xfs_buf_rele( * was on was the disposal list */ if (!(bp->b_state & XFS_BSTATE_DISPOSE)) { - list_lru_del(&bp->b_target->bt_lru, &bp->b_lru); + list_lru_del_obj(&bp->b_target->bt_lru, &bp->b_lru); } else { ASSERT(list_empty(&bp->b_lru)); } diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index ac6ba646624d..49f619f5aa96 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -1064,7 +1064,7 @@ xfs_qm_dqput( struct xfs_quotainfo *qi = dqp->q_mount->m_quotainfo; trace_xfs_dqput_free(dqp);

- if (list_lru_add(&qi->qi_lru, &dqp->q_lru)) + if (list_lru_add_obj(&qi->qi_lru, &dqp->q_lru)) XFS_STATS_INC(dqp->q_mount, xs_qm_dquot_unused); } xfs_dqunlock(dqp); diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 94a7932ac570..67d0a8564ff3 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -171,7 +171,7 @@ xfs_qm_dqpurge( * hits zero, so it really should be on the freelist here. */ ASSERT(!list_empty(&dqp->q_lru)); - list_lru_del(&qi->qi_lru, &dqp->q_lru); + list_lru_del_obj(&qi->qi_lru, &dqp->q_lru); XFS_STATS_DEC(dqp->q_mount, xs_qm_dquot_unused);

xfs_qm_dqdestroy(dqp); diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h index b35968ee9fb5..5ef217443299 100644 --- a/include/linux/list_lru.h +++ b/include/linux/list_lru.h @@ -75,6 +75,8 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren * list_lru_add: add an element to the lru list's tail * @list_lru: the lru pointer * @item: the item to be added. + * @memcg: the cgroup of the sublist to add the item to. + * @nid: the node id of the sublist to add the item to. * * If the element is already part of a list, this function returns doing * nothing. Therefore the caller does not need to keep state about whether or @@ -87,12 +89,28 @@ void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *paren * * Return value: true if the list was updated, false otherwise */ -bool list_lru_add(struct list_lru *lru, struct list_head *item); +bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg);

/** - * list_lru_del: delete an element to the lru list + * list_lru_add_obj: add an element to the lru list's tail + * @list_lru: the lru pointer + * @item: the item to be added. + * + * This function is similar to list_lru_add(), but the NUMA node and the + * memcg of the sublist is determined by @item list_head. This assumption is + * valid for slab objects LRU such as dentries, inodes, etc. + * + * Return value: true if the list was updated, false otherwise + */ +bool list_lru_add_obj(struct list_lru *lru, struct list_head *item); + +/** + * list_lru_del: delete an element from the lru list * @list_lru: the lru pointer * @item: the item to be deleted. + * @memcg: the cgroup of the sublist to delete the item from. + * @nid: the node id of the sublist to delete the item from. * * This function works analogously as list_lru_add in terms of list * manipulation. The comments about an element already pertaining to @@ -100,7 +118,21 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item); * * Return value: true if the list was updated, false otherwise */ -bool list_lru_del(struct list_lru *lru, struct list_head *item); +bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg); + +/** + * list_lru_del_obj: delete an element from the lru list + * @list_lru: the lru pointer + * @item: the item to be deleted. + * + * This function is similar to list_lru_del(), but the NUMA node and the + * memcg of the sublist is determined by @item list_head. This assumption is + * valid for slab objects LRU such as dentries, inodes, etc. + * + * Return value: true if the list was updated, false otherwise. + */ +bool list_lru_del_obj(struct list_lru *lru, struct list_head *item);

/** * list_lru_count_one: return the number of objects currently held by @lru @@ -136,6 +168,14 @@ static inline unsigned long list_lru_count(struct list_lru *lru) void list_lru_isolate(struct list_lru_one *list, struct list_head *item); void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item, struct list_head *head); +/* + * list_lru_putback: undo list_lru_isolate. + * + * Since we might have dropped the LRU lock in between, recompute list_lru_one + * from the node's id and memcg. + */ +void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg);

typedef enum lru_status (*list_lru_walk_cb)(struct list_head *item, struct list_lru_one *list, spinlock_t *lock, void *cb_arg); diff --git a/mm/list_lru.c b/mm/list_lru.c index a05e5bef3b40..fcca67ac26ec 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -116,21 +116,19 @@ list_lru_from_kmem(struct list_lru *lru, int nid, void *ptr, } #endif /* CONFIG_MEMCG_KMEM */

-bool list_lru_add(struct list_lru *lru, struct list_head *item) +bool list_lru_add(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) { - int nid = page_to_nid(virt_to_page(item)); struct list_lru_node *nlru = &lru->node[nid]; - struct mem_cgroup *memcg; struct list_lru_one *l;

spin_lock(&nlru->lock); if (list_empty(item)) { - l = list_lru_from_kmem(lru, nid, item, &memcg); + l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); list_add_tail(item, &l->list); /* Set shrinker bit if the first element was added */ if (!l->nr_items++) - set_shrinker_bit(memcg, nid, - lru_shrinker_id(lru)); + set_shrinker_bit(memcg, nid, lru_shrinker_id(lru)); nlru->nr_items++; spin_unlock(&nlru->lock); return true; @@ -140,15 +138,25 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item) } EXPORT_SYMBOL_GPL(list_lru_add);

-bool list_lru_del(struct list_lru *lru, struct list_head *item) +bool list_lru_add_obj(struct list_lru *lru, struct list_head *item) { int nid = page_to_nid(virt_to_page(item)); + struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? + mem_cgroup_from_slab_obj(item) : NULL; + + return list_lru_add(lru, item, nid, memcg); +} +EXPORT_SYMBOL_GPL(list_lru_add_obj); + +bool list_lru_del(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) +{ struct list_lru_node *nlru = &lru->node[nid]; struct list_lru_one *l;

spin_lock(&nlru->lock); if (!list_empty(item)) { - l = list_lru_from_kmem(lru, nid, item, NULL); + l = list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); list_del_init(item); l->nr_items--; nlru->nr_items--; @@ -160,6 +168,16 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item) } EXPORT_SYMBOL_GPL(list_lru_del);

+bool list_lru_del_obj(struct list_lru *lru, struct list_head *item) +{ + int nid = page_to_nid(virt_to_page(item)); + struct mem_cgroup *memcg = list_lru_memcg_aware(lru) ? + mem_cgroup_from_slab_obj(item) : NULL; + + return list_lru_del(lru, item, nid, memcg); +} +EXPORT_SYMBOL_GPL(list_lru_del_obj); + void list_lru_isolate(struct list_lru_one *list, struct list_head *item) { list_del_init(item); @@ -175,6 +193,20 @@ void list_lru_isolate_move(struct list_lru_one *list, struct list_head *item, } EXPORT_SYMBOL_GPL(list_lru_isolate_move);

+void list_lru_putback(struct list_lru *lru, struct list_head *item, int nid, + struct mem_cgroup *memcg) +{ + struct list_lru_one *list = + list_lru_from_memcg_idx(lru, nid, memcg_kmem_id(memcg)); + + if (list_empty(item)) { + list_add_tail(item, &list->list); + if (!list->nr_items++) + set_shrinker_bit(memcg, nid, lru_shrinker_id(lru)); + } +} +EXPORT_SYMBOL_GPL(list_lru_putback); + unsigned long list_lru_count_one(struct list_lru *lru, int nid, struct mem_cgroup *memcg) { diff --git a/mm/workingset.c b/mm/workingset.c index 11045febc383..7d3dacab8451 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -631,12 +631,12 @@ void workingset_update_node(struct xa_node *node)

if (node->count && node->count == node->nr_values) { if (list_empty(&node->private_list)) { - list_lru_add(&shadow_nodes, &node->private_list); + list_lru_add_obj(&shadow_nodes, &node->private_list); __inc_lruvec_kmem_state(node, WORKINGSET_NODES); } } else { if (!list_empty(&node->private_list)) { - list_lru_del(&shadow_nodes, &node->private_list); + list_lru_del_obj(&shadow_nodes, &node->private_list); __dec_lruvec_kmem_state(node, WORKINGSET_NODES); } }

From: Domenico Cerasuolo cerasuolodomenico@gmail.com

Since zswap now writes back pages from memcg-specific LRUs, we now need a new stat to show writebacks count for each memcg.

Suggested-by: Nhat Pham nphamcs@gmail.com Signed-off-by: Domenico Cerasuolo cerasuolodomenico@gmail.com Signed-off-by: Nhat Pham nphamcs@gmail.com --- include/linux/vm_event_item.h | 1 + mm/memcontrol.c | 1 + mm/vmstat.c | 1 + mm/zswap.c | 3 +++ 4 files changed, 6 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 8abfa1240040..3153359c3841 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -145,6 +145,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, #ifdef CONFIG_ZSWAP ZSWPIN, ZSWPOUT, + ZSWP_WB, #endif #ifdef CONFIG_X86 DIRECT_MAP_LEVEL2_SPLIT, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 61c0c46c2d62..568d9d037a59 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -593,6 +593,7 @@ static const unsigned int memcg_vm_event_stat[] = { #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP) ZSWPIN, ZSWPOUT, + ZSWP_WB, #endif #ifdef CONFIG_TRANSPARENT_HUGEPAGE THP_FAULT_ALLOC, diff --git a/mm/vmstat.c b/mm/vmstat.c index 359460deb377..5e5572f3b456 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = { #ifdef CONFIG_ZSWAP "zswpin", "zswpout", + "zswp_wb", #endif #ifdef CONFIG_X86 "direct_map_level2_splits", diff --git a/mm/zswap.c b/mm/zswap.c index ee8e227e7b0b..b87311e48de9 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -711,6 +711,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o } zswap_written_back_pages++;

+ if (entry->objcg) + count_objcg_event(entry->objcg, ZSWP_WB); + /* * Writeback started successfully, the page now belongs to the * swapcache. Drop the entry from zswap - unless invalidate already

Currently, we only shrink the zswap pool when the user-defined limit is hit. This means that if we set the limit too high, cold data that are unlikely to be used again will reside in the pool, wasting precious memory. It is hard to predict how much zswap space will be needed ahead of time, as this depends on the workload (specifically, on factors such as memory access patterns and compressibility of the memory pages).

This patch implements a memcg- and NUMA-aware shrinker for zswap, that is initiated when there is memory pressure. The shrinker does not have any parameter that must be tuned by the user, and can be opted in or out on a per-memcg basis.

Furthermore, to make it more robust for many workloads and prevent overshrinking (i.e evicting warm pages that might be refaulted into memory), we build in the following heuristics:

* Estimate the number of warm pages residing in zswap, and attempt to protect this region of the zswap LRU. * Scale the number of freeable objects by an estimate of the memory saving factor. The better zswap compresses the data, the fewer pages we will evict to swap (as we will otherwise incur IO for relatively small memory saving). * During reclaim, if the shrinker encounters a page that is also being brought into memory, the shrinker will cautiously terminate its shrinking action, as this is a sign that it is touching the warmer region of the zswap LRU.

As a proof of concept, we ran the following synthetic benchmark: build the linux kernel in a memory-limited cgroup, and allocate some cold data in tmpfs to see if the shrinker could write them out and improved the overall performance. Depending on the amount of cold data generated, we observe from 14% to 35% reduction in kernel CPU time used in the kernel builds.

Signed-off-by: Nhat Pham nphamcs@gmail.com --- Documentation/admin-guide/mm/zswap.rst | 7 + include/linux/mmzone.h | 2 + include/linux/zswap.h | 25 +++- mm/mmzone.c | 1 + mm/swap_state.c | 2 + mm/zswap.c | 178 ++++++++++++++++++++++++- 6 files changed, 208 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst index 45b98390e938..522ae22ccb84 100644 --- a/Documentation/admin-guide/mm/zswap.rst +++ b/Documentation/admin-guide/mm/zswap.rst @@ -153,6 +153,13 @@ attribute, e. g.::

Setting this parameter to 100 will disable the hysteresis.

+When there is a sizable amount of cold memory residing in the zswap pool, it +can be advantageous to proactively write these cold pages to swap and reclaim +the memory for other use cases. By default, the zswap shrinker is disabled. +User can enable it as follows: + + echo Y > /sys/module/zswap/parameters/shrinker_enabled + A debugfs interface is provided for various statistic about pool size, number of pages stored, same-value filled pages and various counters for the reasons pages are rejected. diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 12f31633be05..633afdb96c40 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -22,6 +22,7 @@ #include <linux/mm_types.h> #include <linux/page-flags.h> #include <linux/local_lock.h> +#include <linux/zswap.h> #include <asm/page.h>

/* Free memory management - zoned buddy allocator. */ @@ -637,6 +638,7 @@ struct lruvec { #ifdef CONFIG_MEMCG struct pglist_data *pgdat; #endif + struct zswap_lruvec_state zswap_lruvec_state; };

/* Isolate for asynchronous migration */ diff --git a/include/linux/zswap.h b/include/linux/zswap.h index 2a60ce39cfde..64d0c3644185 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -5,19 +5,39 @@ #include <linux/types.h> #include <linux/mm_types.h>

+struct lruvec; + extern u64 zswap_pool_total_size; extern atomic_t zswap_stored_pages;

#ifdef CONFIG_ZSWAP

+struct zswap_lruvec_state { + /* + * Number of pages in zswap that should be protected from the shrinker. + * This number is an estimate of the following counts: + * + * a) Recent page faults. + * b) Recent insertion to the zswap LRU. This includes new zswap stores, + * as well as recent zswap LRU rotations. + * + * These pages are likely to be warm, and might incur IO if the are written + * to swap. + */ + atomic_long_t nr_zswap_protected; +}; + bool zswap_store(struct folio *folio); bool zswap_load(struct folio *folio); void zswap_invalidate(int type, pgoff_t offset); void zswap_swapon(int type); void zswap_swapoff(int type); - +void zswap_lruvec_state_init(struct lruvec *lruvec); +void zswap_lruvec_swapin(struct page *page); #else

+struct zswap_lruvec_state {}; + static inline bool zswap_store(struct folio *folio) { return false; @@ -31,7 +51,8 @@ static inline bool zswap_load(struct folio *folio) static inline void zswap_invalidate(int type, pgoff_t offset) {} static inline void zswap_swapon(int type) {} static inline void zswap_swapoff(int type) {} - +static inline void zswap_lruvec_init(struct lruvec *lruvec) {} +static inline void zswap_lruvec_swapin(struct page *page) {} #endif

#endif /* _LINUX_ZSWAP_H */ diff --git a/mm/mmzone.c b/mm/mmzone.c index b594d3f268fe..c01896eca736 100644 --- a/mm/mmzone.c +++ b/mm/mmzone.c @@ -78,6 +78,7 @@ void lruvec_init(struct lruvec *lruvec)

memset(lruvec, 0, sizeof(struct lruvec)); spin_lock_init(&lruvec->lru_lock); + zswap_lruvec_state_init(lruvec);

for_each_lru(lru) INIT_LIST_HEAD(&lruvec->lists[lru]); diff --git a/mm/swap_state.c b/mm/swap_state.c index 040639e1c77e..38ce9981b0be 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -686,6 +686,7 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, &page_allocated, false); if (unlikely(page_allocated)) swap_readpage(page, false, NULL); + zswap_lruvec_swapin(page); return page; }

@@ -861,6 +862,7 @@ static struct page *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask, &page_allocated, false); if (unlikely(page_allocated)) swap_readpage(page, false, NULL); + zswap_lruvec_swapin(page); return page; }

diff --git a/mm/zswap.c b/mm/zswap.c index b87311e48de9..c40697f07ba3 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -146,6 +146,10 @@ module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644); /* Number of zpools in zswap_pool (empirically determined for scalability) */ #define ZSWAP_NR_ZPOOLS 32

+/* Enable/disable memory pressure-based shrinker. */ +static bool zswap_shrinker_enabled; +module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644); + /********************************* * data structures **********************************/ @@ -175,6 +179,8 @@ struct zswap_pool { char tfm_name[CRYPTO_MAX_ALG_NAME]; struct list_lru list_lru; struct mem_cgroup *next_shrink; + struct shrinker *shrinker; + atomic_t nr_stored; };

/* @@ -273,17 +279,26 @@ static bool zswap_can_accept(void) DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE); }

+static u64 get_zswap_pool_size(struct zswap_pool *pool) +{ + u64 pool_size = 0; + int i; + + for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) + pool_size += zpool_get_total_size(pool->zpools[i]); + + return pool_size; +} + static void zswap_update_total_size(void) { struct zswap_pool *pool; u64 total = 0; - int i;

rcu_read_lock();

list_for_each_entry_rcu(pool, &zswap_pools, list) - for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) - total += zpool_get_total_size(pool->zpools[i]); + total += get_zswap_pool_size(pool);

rcu_read_unlock();

@@ -321,6 +336,24 @@ static void zswap_entry_cache_free(struct zswap_entry *entry) kmem_cache_free(zswap_entry_cache, entry); }

+/********************************* +* zswap lruvec functions +**********************************/ +void zswap_lruvec_state_init(struct lruvec *lruvec) +{ + atomic_long_set(&lruvec->zswap_lruvec_state.nr_zswap_protected, 0); +} + +void zswap_lruvec_swapin(struct page *page) +{ + struct lruvec *lruvec; + + if (page) { + lruvec = folio_lruvec(page_folio(page)); + atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected); + } +} + /********************************* * lru functions **********************************/ @@ -328,8 +361,24 @@ static bool zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry) { struct mem_cgroup *memcg = get_mem_cgroup_from_entry(entry); int nid = entry_to_nid(entry); + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid)); bool added = list_lru_add(list_lru, &entry->lru, nid, memcg); + atomic_long_t *nr_zswap_protected = + &lruvec->zswap_lruvec_state.nr_zswap_protected; + unsigned long lru_size, old, new;

+ if (added) { + lru_size = list_lru_count_one(list_lru, nid, memcg); + old = atomic_long_inc_return(nr_zswap_protected); + + /* + * Decay to avoid overflow and adapt to changing workloads. + * This is based on LRU reclaim cost decaying heuristics. + */ + do { + new = old > lru_size / 4 ? old / 2 : old; + } while (!atomic_long_try_cmpxchg(nr_zswap_protected, &old, new)); + } mem_cgroup_put(memcg); return added; } @@ -430,6 +479,7 @@ static void zswap_free_entry(struct zswap_entry *entry) else { zswap_lru_del(&entry->pool->list_lru, entry); zpool_free(zswap_find_zpool(entry), entry->handle); + atomic_dec(&entry->pool->nr_stored); zswap_pool_put(entry->pool); } zswap_entry_cache_free(entry); @@ -471,6 +521,95 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root, return entry; }

+/********************************* +* shrinker functions +**********************************/ +static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l, + spinlock_t *lock, void *arg); + +static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, + struct shrink_control *sc) +{ + struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid)); + unsigned long shrink_ret, nr_protected, lru_size; + struct zswap_pool *pool = shrinker->private_data; + bool encountered_page_in_swapcache = false; + + nr_protected = + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); + lru_size = list_lru_shrink_count(&pool->list_lru, sc); + + /* + * Abort if the shrinker is disabled or if we are shrinking into the + * protected region. + */ + if (!zswap_shrinker_enabled || nr_protected >= lru_size - sc->nr_to_scan) { + sc->nr_scanned = 0; + return SHRINK_STOP; + } + + shrink_ret = list_lru_shrink_walk(&pool->list_lru, sc, &shrink_memcg_cb, + &encountered_page_in_swapcache); + + if (encountered_page_in_swapcache) + return SHRINK_STOP; + + return shrink_ret ? shrink_ret : SHRINK_STOP; +} + +static unsigned long zswap_shrinker_count(struct shrinker *shrinker, + struct shrink_control *sc) +{ + struct zswap_pool *pool = shrinker->private_data; + struct mem_cgroup *memcg = sc->memcg; + struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid)); + unsigned long nr_backing, nr_stored, nr_freeable, nr_protected; + +#ifdef CONFIG_MEMCG_KMEM + cgroup_rstat_flush(memcg->css.cgroup); + nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT; + nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED); +#else + /* use pool stats instead of memcg stats */ + nr_backing = get_zswap_pool_size(pool) >> PAGE_SHIFT; + nr_stored = atomic_read(&pool->nr_stored); +#endif + + if (!zswap_shrinker_enabled || !nr_stored) + return 0; + + nr_protected = + atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); + nr_freeable = list_lru_shrink_count(&pool->list_lru, sc); + /* + * Subtract the lru size by an estimate of the number of pages + * that should be protected. + */ + nr_freeable = nr_freeable > nr_protected ? nr_freeable - nr_protected : 0; + + /* + * Scale the number of freeable pages by the memory saving factor. + * This ensures that the better zswap compresses memory, the fewer + * pages we will evict to swap (as it will otherwise incur IO for + * relatively small memory saving). + */ + return mult_frac(nr_freeable, nr_backing, nr_stored); +} + +static void zswap_alloc_shrinker(struct zswap_pool *pool) +{ + pool->shrinker = + shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap"); + if (!pool->shrinker) + return; + + pool->shrinker->private_data = pool; + pool->shrinker->scan_objects = zswap_shrinker_scan; + pool->shrinker->count_objects = zswap_shrinker_count; + pool->shrinker->batch = 0; + pool->shrinker->seeks = DEFAULT_SEEKS; +} + /********************************* * per-cpu code **********************************/ @@ -666,8 +805,10 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o spinlock_t *lock, void *arg) { struct zswap_entry *entry = container_of(item, struct zswap_entry, lru); + bool *encountered_page_in_swapcache = (bool *)arg; struct mem_cgroup *memcg; struct zswap_tree *tree; + struct lruvec *lruvec; pgoff_t swpoffset; enum lru_status ret = LRU_REMOVED_RETRY; int writeback_result; @@ -705,8 +846,22 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o /* we cannot use zswap_lru_add here, because it increments node's lru count */ list_lru_putback(&entry->pool->list_lru, item, entry_to_nid(entry), memcg); spin_unlock(lock); - mem_cgroup_put(memcg); ret = LRU_RETRY; + + /* + * Encountering a page already in swap cache is a sign that we are shrinking + * into the warmer region. We should terminate shrinking (if we're in the dynamic + * shrinker context). + */ + if (writeback_result == -EEXIST && encountered_page_in_swapcache) { + ret = LRU_SKIP; + *encountered_page_in_swapcache = true; + } + lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(entry_to_nid(entry))); + /* Increment the protection area to account for the LRU rotation. */ + atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected); + + mem_cgroup_put(memcg); goto put_unlock; } zswap_written_back_pages++; @@ -826,6 +981,11 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) &pool->node); if (ret) goto error; + + zswap_alloc_shrinker(pool); + if (!pool->shrinker) + goto error; + pr_debug("using %s compressor\n", pool->tfm_name);

/* being the current pool takes 1 ref; this func expects the @@ -833,13 +993,19 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) */ kref_init(&pool->kref); INIT_LIST_HEAD(&pool->list); - list_lru_init_memcg(&pool->list_lru, NULL); + if (list_lru_init_memcg(&pool->list_lru, pool->shrinker)) + goto lru_fail; + shrinker_register(pool->shrinker); INIT_WORK(&pool->shrink_work, shrink_worker); + atomic_set(&pool->nr_stored, 0);

zswap_pool_debug("created", pool);

return pool;

+lru_fail: + list_lru_destroy(&pool->list_lru); + shrinker_free(pool->shrinker); error: if (pool->acomp_ctx) free_percpu(pool->acomp_ctx); @@ -897,6 +1063,7 @@ static void zswap_pool_destroy(struct zswap_pool *pool)

zswap_pool_debug("destroying", pool);

+ shrinker_free(pool->shrinker); cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node); free_percpu(pool->acomp_ctx); list_lru_destroy(&pool->list_lru); @@ -1443,6 +1610,7 @@ bool zswap_store(struct folio *folio) if (entry->length) { INIT_LIST_HEAD(&entry->lru); zswap_lru_add(&entry->pool->list_lru, entry); + atomic_inc(&entry->pool->nr_stored); } spin_unlock(&tree->lock);