Merge tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull MM updates from Andrew Morton: "Many singleton patches against the MM code. The patch series which are included in this merge do the following: - Kemeng Shi has contributed some compation maintenance work in the series 'Fixes and cleanups to compaction' - Joel Fernandes has a patchset ('Optimize mremap during mutual alignment within PMD') which fixes an obscure issue with mremap()'s pagetable handling during a subsequent exec(), based upon an implementation which Linus suggested - More DAMON/DAMOS maintenance and feature work from SeongJae Park i the following patch series: mm/damon: misc fixups for documents, comments and its tracepoint mm/damon: add a tracepoint for damos apply target regions mm/damon: provide pseudo-moving sum based access rate mm/damon: implement DAMOS apply intervals mm/damon/core-test: Fix memory leaks in core-test mm/damon/sysfs-schemes: Do DAMOS tried regions update for only one apply interval - In the series 'Do not try to access unaccepted memory' Adrian Hunter provides some fixups for the recently-added 'unaccepted memory' feature. To increase the feature's checking coverage. 'Plug a few gaps where RAM is exposed without checking if it is unaccepted memory' - In the series 'cleanups for lockless slab shrink' Qi Zheng has done some maintenance work which is preparation for the lockless slab shrinking code - Qi Zheng has redone the earlier (and reverted) attempt to make slab shrinking lockless in the series 'use refcount+RCU method to implement lockless slab shrink' - David Hildenbrand contributes some maintenance work for the rmap code in the series 'Anon rmap cleanups' - Kefeng Wang does more folio conversions and some maintenance work in the migration code. Series 'mm: migrate: more folio conversion and unification' - Matthew Wilcox has fixed an issue in the buffer_head code which was causing long stalls under some heavy memory/IO loads. Some cleanups were added on the way. Series 'Add and use bdev_getblk()' - In the series 'Use nth_page() in place of direct struct page manipulation' Zi Yan has fixed a potential issue with the direct manipulation of hugetlb page frames - In the series 'mm: hugetlb: Skip initialization of gigantic tail struct pages if freed by HVO' has improved our handling of gigantic pages in the hugetlb vmmemmep optimizaton code. This provides significant boot time improvements when significant amounts of gigantic pages are in use - Matthew Wilcox has sent the series 'Small hugetlb cleanups' - code rationalization and folio conversions in the hugetlb code - Yin Fengwei has improved mlock()'s handling of large folios in the series 'support large folio for mlock' - In the series 'Expose swapcache stat for memcg v1' Liu Shixin has added statistics for memcg v1 users which are available (and useful) under memcg v2 - Florent Revest has enhanced the MDWE (Memory-Deny-Write-Executable) prctl so that userspace may direct the kernel to not automatically propagate the denial to child processes. The series is named 'MDWE without inheritance' - Kefeng Wang has provided the series 'mm: convert numa balancing functions to use a folio' which does what it says - In the series 'mm/ksm: add fork-exec support for prctl' Stefan Roesch makes is possible for a process to propagate KSM treatment across exec() - Huang Ying has enhanced memory tiering's calculation of memory distances. This is used to permit the dax/kmem driver to use 'high bandwidth memory' in addition to Optane Data Center Persistent Memory Modules (DCPMM). The series is named 'memory tiering: calculate abstract distance based on ACPI HMAT' - In the series 'Smart scanning mode for KSM' Stefan Roesch has optimized KSM by teaching it to retain and use some historical information from previous scans - Yosry Ahmed has fixed some inconsistencies in memcg statistics in the series 'mm: memcg: fix tracking of pending stats updates values' - In the series 'Implement IOCTL to get and optionally clear info about PTEs' Peter Xu has added an ioctl to /proc/<pid>/pagemap which permits us to atomically read-then-clear page softdirty state. This is mainly used by CRIU - Hugh Dickins contributed the series 'shmem,tmpfs: general maintenance', a bunch of relatively minor maintenance tweaks to this code - Matthew Wilcox has increased the use of the VMA lock over file-backed page faults in the series 'Handle more faults under the VMA lock'. Some rationalizations of the fault path became possible as a result - In the series 'mm/rmap: convert page_move_anon_rmap() to folio_move_anon_rmap()' David Hildenbrand has implemented some cleanups and folio conversions - In the series 'various improvements to the GUP interface' Lorenzo Stoakes has simplified and improved the GUP interface with an eye to providing groundwork for future improvements - Andrey Konovalov has sent along the series 'kasan: assorted fixes and improvements' which does those things - Some page allocator maintenance work from Kemeng Shi in the series 'Two minor cleanups to break_down_buddy_pages' - In thes series 'New selftest for mm' Breno Leitao has developed another MM self test which tickles a race we had between madvise() and page faults - In the series 'Add folio_end_read' Matthew Wilcox provides cleanups and an optimization to the core pagecache code - Nhat Pham has added memcg accounting for hugetlb memory in the series 'hugetlb memcg accounting' - Cleanups and rationalizations to the pagemap code from Lorenzo Stoakes, in the series 'Abstract vma_merge() and split_vma()' - Audra Mitchell has fixed issues in the procfs page_owner code's new timestamping feature which was causing some misbehaviours. In the series 'Fix page_owner's use of free timestamps' - Lorenzo Stoakes has fixed the handling of new mappings of sealed files in the series 'permit write-sealed memfd read-only shared mappings' - Mike Kravetz has optimized the hugetlb vmemmap optimization in the series 'Batch hugetlb vmemmap modification operations' - Some buffer_head folio conversions and cleanups from Matthew Wilcox in the series 'Finish the create_empty_buffers() transition' - As a page allocator performance optimization Huang Ying has added automatic tuning to the allocator's per-cpu-pages feature, in the series 'mm: PCP high auto-tuning' - Roman Gushchin has contributed the patchset 'mm: improve performance of accounted kernel memory allocations' which improves their performance by ~30% as measured by a micro-benchmark - folio conversions from Kefeng Wang in the series 'mm: convert page cpupid functions to folios' - Some kmemleak fixups in Liu Shixin's series 'Some bugfix about kmemleak' - Qi Zheng has improved our handling of memoryless nodes by keeping them off the allocation fallback list. This is done in the series 'handle memoryless nodes more appropriately' - khugepaged conversions from Vishal Moola in the series 'Some khugepaged folio conversions'" [ bcachefs conflicts with the dynamically allocated shrinkers have been resolved as per Stephen Rothwell in https://lore.kernel.org/all/20230913093553.4290421e@canb.auug.org.au/ with help from Qi Zheng. The clone3 test filtering conflict was half-arsed by yours truly ] * tag 'mm-stable-2023-11-01-14-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (406 commits) mm/damon/sysfs: update monitoring target regions for online input commit mm/damon/sysfs: remove requested targets when online-commit inputs selftests: add a sanity check for zswap Documentation: maple_tree: fix word spelling error mm/vmalloc: fix the unchecked dereference warning in vread_iter() zswap: export compression failure stats Documentation: ubsan: drop "the" from article title mempolicy: migration attempt to match interleave nodes mempolicy: mmap_lock is not needed while migrating folios mempolicy: alloc_pages_mpol() for NUMA policy without vma mm: add page_rmappable_folio() wrapper mempolicy: remove confusing MPOL_MF_LAZY dead code mempolicy: mpol_shared_policy_init() without pseudo-vma mempolicy trivia: use pgoff_t in shared mempolicy tree mempolicy trivia: slightly more consistent naming mempolicy trivia: delete those ancient pr_debug()s mempolicy: fix migrate_pages(2) syscall return nr_failed kernfs: drop shared NUMA mempolicy hooks hugetlbfs: drop shared NUMA mempolicy pretence mm/damon/sysfs-test: add a unit test for damon_sysfs_set_targets() ...
author: Linus Torvalds <torvalds@linux-foundation.org> 2023-11-02 19:38:47 -1000
committer: Linus Torvalds <torvalds@linux-foundation.org> 2023-11-02 19:38:47 -1000
commit: ecae0bd5173b1014f95a14a8dfbe40ec10367dcf (patch)
tree: f571213ef1a35354ea79f0240a180fdb4111b290 /mm/shrinker.c
parent: bc3012f4e3a9765de81f454cb8f9bb16aafc6ff5 (diff)
parent: 9732336006764e2ee61225387e3c70eae9139035 (diff)
download: lwn-ecae0bd5173b1014f95a14a8dfbe40ec10367dcf.tar.gz
lwn-ecae0bd5173b1014f95a14a8dfbe40ec10367dcf.zip
1 files changed, 809 insertions, 0 deletions
diff --git a/mm/shrinker.c b/mm/shrinker.c
new file mode 100644
index 000000000000..dd91eab43ed3
--- /dev/null
+++ b/mm/shrinker.c
@@ -0,0 +1,809 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/memcontrol.h>
+#include <linux/rwsem.h>
+#include <linux/shrinker.h>
+#include <linux/rculist.h>
+#include <trace/events/vmscan.h>
+
+#include "internal.h"
+
+LIST_HEAD(shrinker_list);
+DEFINE_MUTEX(shrinker_mutex);
+
+#ifdef CONFIG_MEMCG
+static int shrinker_nr_max;
+
+static inline int shrinker_unit_size(int nr_items)
+{
+	return (DIV_ROUND_UP(nr_items, SHRINKER_UNIT_BITS) * sizeof(struct shrinker_info_unit *));
+}
+
+static inline void shrinker_unit_free(struct shrinker_info *info, int start)
+{
+	struct shrinker_info_unit **unit;
+	int nr, i;
+
+	if (!info)
+		return;
+
+	unit = info->unit;
+	nr = DIV_ROUND_UP(info->map_nr_max, SHRINKER_UNIT_BITS);
+
+	for (i = start; i < nr; i++) {
+		if (!unit[i])
+			break;
+
+		kfree(unit[i]);
+		unit[i] = NULL;
+	}
+}
+
+static inline int shrinker_unit_alloc(struct shrinker_info *new,
+				       struct shrinker_info *old, int nid)
+{
+	struct shrinker_info_unit *unit;
+	int nr = DIV_ROUND_UP(new->map_nr_max, SHRINKER_UNIT_BITS);
+	int start = old ? DIV_ROUND_UP(old->map_nr_max, SHRINKER_UNIT_BITS) : 0;
+	int i;
+
+	for (i = start; i < nr; i++) {
+		unit = kzalloc_node(sizeof(*unit), GFP_KERNEL, nid);
+		if (!unit) {
+			shrinker_unit_free(new, start);
+			return -ENOMEM;
+		}
+
+		new->unit[i] = unit;
+	}
+
+	return 0;
+}
+
+void free_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct mem_cgroup_per_node *pn;
+	struct shrinker_info *info;
+	int nid;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		info = rcu_dereference_protected(pn->shrinker_info, true);
+		shrinker_unit_free(info, 0);
+		kvfree(info);
+		rcu_assign_pointer(pn->shrinker_info, NULL);
+	}
+}
+
+int alloc_shrinker_info(struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	int nid, ret = 0;
+	int array_size = 0;
+
+	mutex_lock(&shrinker_mutex);
+	array_size = shrinker_unit_size(shrinker_nr_max);
+	for_each_node(nid) {
+		info = kvzalloc_node(sizeof(*info) + array_size, GFP_KERNEL, nid);
+		if (!info)
+			goto err;
+		info->map_nr_max = shrinker_nr_max;
+		if (shrinker_unit_alloc(info, NULL, nid))
+			goto err;
+		rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
+	}
+	mutex_unlock(&shrinker_mutex);
+
+	return ret;
+
+err:
+	mutex_unlock(&shrinker_mutex);
+	free_shrinker_info(memcg);
+	return -ENOMEM;
+}
+
+static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
+						     int nid)
+{
+	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
+					 lockdep_is_held(&shrinker_mutex));
+}
+
+static int expand_one_shrinker_info(struct mem_cgroup *memcg, int new_size,
+				    int old_size, int new_nr_max)
+{
+	struct shrinker_info *new, *old;
+	struct mem_cgroup_per_node *pn;
+	int nid;
+
+	for_each_node(nid) {
+		pn = memcg->nodeinfo[nid];
+		old = shrinker_info_protected(memcg, nid);
+		/* Not yet online memcg */
+		if (!old)
+			return 0;
+
+		/* Already expanded this shrinker_info */
+		if (new_nr_max <= old->map_nr_max)
+			continue;
+
+		new = kvmalloc_node(sizeof(*new) + new_size, GFP_KERNEL, nid);
+		if (!new)
+			return -ENOMEM;
+
+		new->map_nr_max = new_nr_max;
+
+		memcpy(new->unit, old->unit, old_size);
+		if (shrinker_unit_alloc(new, old, nid)) {
+			kvfree(new);
+			return -ENOMEM;
+		}
+
+		rcu_assign_pointer(pn->shrinker_info, new);
+		kvfree_rcu(old, rcu);
+	}
+
+	return 0;
+}
+
+static int expand_shrinker_info(int new_id)
+{
+	int ret = 0;
+	int new_nr_max = round_up(new_id + 1, SHRINKER_UNIT_BITS);
+	int new_size, old_size = 0;
+	struct mem_cgroup *memcg;
+
+	if (!root_mem_cgroup)
+		goto out;
+
+	lockdep_assert_held(&shrinker_mutex);
+
+	new_size = shrinker_unit_size(new_nr_max);
+	old_size = shrinker_unit_size(shrinker_nr_max);
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		ret = expand_one_shrinker_info(memcg, new_size, old_size,
+					       new_nr_max);
+		if (ret) {
+			mem_cgroup_iter_break(NULL, memcg);
+			goto out;
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
+out:
+	if (!ret)
+		shrinker_nr_max = new_nr_max;
+
+	return ret;
+}
+
+static inline int shrinker_id_to_index(int shrinker_id)
+{
+	return shrinker_id / SHRINKER_UNIT_BITS;
+}
+
+static inline int shrinker_id_to_offset(int shrinker_id)
+{
+	return shrinker_id % SHRINKER_UNIT_BITS;
+}
+
+static inline int calc_shrinker_id(int index, int offset)
+{
+	return index * SHRINKER_UNIT_BITS + offset;
+}
+
+void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
+{
+	if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
+		struct shrinker_info *info;
+		struct shrinker_info_unit *unit;
+
+		rcu_read_lock();
+		info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+		unit = info->unit[shrinker_id_to_index(shrinker_id)];
+		if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
+			/* Pairs with smp mb in shrink_slab() */
+			smp_mb__before_atomic();
+			set_bit(shrinker_id_to_offset(shrinker_id), unit->map);
+		}
+		rcu_read_unlock();
+	}
+}
+
+static DEFINE_IDR(shrinker_idr);
+
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
+{
+	int id, ret = -ENOMEM;
+
+	if (mem_cgroup_disabled())
+		return -ENOSYS;
+
+	mutex_lock(&shrinker_mutex);
+	id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
+	if (id < 0)
+		goto unlock;
+
+	if (id >= shrinker_nr_max) {
+		if (expand_shrinker_info(id)) {
+			idr_remove(&shrinker_idr, id);
+			goto unlock;
+		}
+	}
+	shrinker->id = id;
+	ret = 0;
+unlock:
+	mutex_unlock(&shrinker_mutex);
+	return ret;
+}
+
+static void shrinker_memcg_remove(struct shrinker *shrinker)
+{
+	int id = shrinker->id;
+
+	BUG_ON(id < 0);
+
+	lockdep_assert_held(&shrinker_mutex);
+
+	idr_remove(&shrinker_idr, id);
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
+	long nr_deferred;
+
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	unit = info->unit[shrinker_id_to_index(shrinker->id)];
+	nr_deferred = atomic_long_xchg(&unit->nr_deferred[shrinker_id_to_offset(shrinker->id)], 0);
+	rcu_read_unlock();
+
+	return nr_deferred;
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	struct shrinker_info *info;
+	struct shrinker_info_unit *unit;
+	long nr_deferred;
+
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	unit = info->unit[shrinker_id_to_index(shrinker->id)];
+	nr_deferred =
+		atomic_long_add_return(nr, &unit->nr_deferred[shrinker_id_to_offset(shrinker->id)]);
+	rcu_read_unlock();
+
+	return nr_deferred;
+}
+
+void reparent_shrinker_deferred(struct mem_cgroup *memcg)
+{
+	int nid, index, offset;
+	long nr;
+	struct mem_cgroup *parent;
+	struct shrinker_info *child_info, *parent_info;
+	struct shrinker_info_unit *child_unit, *parent_unit;
+
+	parent = parent_mem_cgroup(memcg);
+	if (!parent)
+		parent = root_mem_cgroup;
+
+	/* Prevent from concurrent shrinker_info expand */
+	mutex_lock(&shrinker_mutex);
+	for_each_node(nid) {
+		child_info = shrinker_info_protected(memcg, nid);
+		parent_info = shrinker_info_protected(parent, nid);
+		for (index = 0; index < shrinker_id_to_index(child_info->map_nr_max); index++) {
+			child_unit = child_info->unit[index];
+			parent_unit = parent_info->unit[index];
+			for (offset = 0; offset < SHRINKER_UNIT_BITS; offset++) {
+				nr = atomic_long_read(&child_unit->nr_deferred[offset]);
+				atomic_long_add(nr, &parent_unit->nr_deferred[offset]);
+			}
+		}
+	}
+	mutex_unlock(&shrinker_mutex);
+}
+#else
+static int shrinker_memcg_alloc(struct shrinker *shrinker)
+{
+	return -ENOSYS;
+}
+
+static void shrinker_memcg_remove(struct shrinker *shrinker)
+{
+}
+
+static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
+				   struct mem_cgroup *memcg)
+{
+	return 0;
+}
+
+static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
+				  struct mem_cgroup *memcg)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+static long xchg_nr_deferred(struct shrinker *shrinker,
+			     struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return xchg_nr_deferred_memcg(nid, shrinker,
+					      sc->memcg);
+
+	return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
+}
+
+
+static long add_nr_deferred(long nr, struct shrinker *shrinker,
+			    struct shrink_control *sc)
+{
+	int nid = sc->nid;
+
+	if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
+		nid = 0;
+
+	if (sc->memcg &&
+	    (shrinker->flags & SHRINKER_MEMCG_AWARE))
+		return add_nr_deferred_memcg(nr, nid, shrinker,
+					     sc->memcg);
+
+	return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
+}
+
+#define SHRINK_BATCH 128
+
+static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
+				    struct shrinker *shrinker, int priority)
+{
+	unsigned long freed = 0;
+	unsigned long long delta;
+	long total_scan;
+	long freeable;
+	long nr;
+	long new_nr;
+	long batch_size = shrinker->batch ? shrinker->batch
+					  : SHRINK_BATCH;
+	long scanned = 0, next_deferred;
+
+	freeable = shrinker->count_objects(shrinker, shrinkctl);
+	if (freeable == 0 || freeable == SHRINK_EMPTY)
+		return freeable;
+
+	/*
+	 * copy the current shrinker scan count into a local variable
+	 * and zero it so that other concurrent shrinker invocations
+	 * don't also do this scanning work.
+	 */
+	nr = xchg_nr_deferred(shrinker, shrinkctl);
+
+	if (shrinker->seeks) {
+		delta = freeable >> priority;
+		delta *= 4;
+		do_div(delta, shrinker->seeks);
+	} else {
+		/*
+		 * These objects don't require any IO to create. Trim
+		 * them aggressively under memory pressure to keep
+		 * them from causing refetches in the IO caches.
+		 */
+		delta = freeable / 2;
+	}
+
+	total_scan = nr >> priority;
+	total_scan += delta;
+	total_scan = min(total_scan, (2 * freeable));
+
+	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
+				   freeable, delta, total_scan, priority);
+
+	/*
+	 * Normally, we should not scan less than batch_size objects in one
+	 * pass to avoid too frequent shrinker calls, but if the slab has less
+	 * than batch_size objects in total and we are really tight on memory,
+	 * we will try to reclaim all available objects, otherwise we can end
+	 * up failing allocations although there are plenty of reclaimable
+	 * objects spread over several slabs with usage less than the
+	 * batch_size.
+	 *
+	 * We detect the "tight on memory" situations by looking at the total
+	 * number of objects we want to scan (total_scan). If it is greater
+	 * than the total number of objects on slab (freeable), we must be
+	 * scanning at high prio and therefore should try to reclaim as much as
+	 * possible.
+	 */
+	while (total_scan >= batch_size ||
+	       total_scan >= freeable) {
+		unsigned long ret;
+		unsigned long nr_to_scan = min(batch_size, total_scan);
+
+		shrinkctl->nr_to_scan = nr_to_scan;
+		shrinkctl->nr_scanned = nr_to_scan;
+		ret = shrinker->scan_objects(shrinker, shrinkctl);
+		if (ret == SHRINK_STOP)
+			break;
+		freed += ret;
+
+		count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
+		total_scan -= shrinkctl->nr_scanned;
+		scanned += shrinkctl->nr_scanned;
+
+		cond_resched();
+	}
+
+	/*
+	 * The deferred work is increased by any new work (delta) that wasn't
+	 * done, decreased by old deferred work that was done now.
+	 *
+	 * And it is capped to two times of the freeable items.
+	 */
+	next_deferred = max_t(long, (nr + delta - scanned), 0);
+	next_deferred = min(next_deferred, (2 * freeable));
+
+	/*
+	 * move the unused scan count back into the shrinker in a
+	 * manner that handles concurrent updates.
+	 */
+	new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
+
+	trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
+	return freed;
+}
+
+#ifdef CONFIG_MEMCG
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	struct shrinker_info *info;
+	unsigned long ret, freed = 0;
+	int offset, index = 0;
+
+	if (!mem_cgroup_online(memcg))
+		return 0;
+
+	/*
+	 * lockless algorithm of memcg shrink.
+	 *
+	 * The shrinker_info may be freed asynchronously via RCU in the
+	 * expand_one_shrinker_info(), so the rcu_read_lock() needs to be used
+	 * to ensure the existence of the shrinker_info.
+	 *
+	 * The shrinker_info_unit is never freed unless its corresponding memcg
+	 * is destroyed. Here we already hold the refcount of memcg, so the
+	 * memcg will not be destroyed, and of course shrinker_info_unit will
+	 * not be freed.
+	 *
+	 * So in the memcg shrink:
+	 *  step 1: use rcu_read_lock() to guarantee existence of the
+	 *          shrinker_info.
+	 *  step 2: after getting shrinker_info_unit we can safely release the
+	 *          RCU lock.
+	 *  step 3: traverse the bitmap and calculate shrinker_id
+	 *  step 4: use rcu_read_lock() to guarantee existence of the shrinker.
+	 *  step 5: use shrinker_id to find the shrinker, then use
+	 *          shrinker_try_get() to guarantee existence of the shrinker,
+	 *          then we can release the RCU lock to do do_shrink_slab() that
+	 *          may sleep.
+	 *  step 6: do shrinker_put() paired with step 5 to put the refcount,
+	 *          if the refcount reaches 0, then wake up the waiter in
+	 *          shrinker_free() by calling complete().
+	 *          Note: here is different from the global shrink, we don't
+	 *                need to acquire the RCU lock to guarantee existence of
+	 *                the shrinker, because we don't need to use this
+	 *                shrinker to traverse the next shrinker in the bitmap.
+	 *  step 7: we have already exited the read-side of rcu critical section
+	 *          before calling do_shrink_slab(), the shrinker_info may be
+	 *          released in expand_one_shrinker_info(), so go back to step 1
+	 *          to reacquire the shrinker_info.
+	 */
+again:
+	rcu_read_lock();
+	info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
+	if (unlikely(!info))
+		goto unlock;
+
+	if (index < shrinker_id_to_index(info->map_nr_max)) {
+		struct shrinker_info_unit *unit;
+
+		unit = info->unit[index];
+
+		rcu_read_unlock();
+
+		for_each_set_bit(offset, unit->map, SHRINKER_UNIT_BITS) {
+			struct shrink_control sc = {
+				.gfp_mask = gfp_mask,
+				.nid = nid,
+				.memcg = memcg,
+			};
+			struct shrinker *shrinker;
+			int shrinker_id = calc_shrinker_id(index, offset);
+
+			rcu_read_lock();
+			shrinker = idr_find(&shrinker_idr, shrinker_id);
+			if (unlikely(!shrinker || !shrinker_try_get(shrinker))) {
+				clear_bit(offset, unit->map);
+				rcu_read_unlock();
+				continue;
+			}
+			rcu_read_unlock();
+
+			/* Call non-slab shrinkers even though kmem is disabled */
+			if (!memcg_kmem_online() &&
+			    !(shrinker->flags & SHRINKER_NONSLAB))
+				continue;
+
+			ret = do_shrink_slab(&sc, shrinker, priority);
+			if (ret == SHRINK_EMPTY) {
+				clear_bit(offset, unit->map);
+				/*
+				 * After the shrinker reported that it had no objects to
+				 * free, but before we cleared the corresponding bit in
+				 * the memcg shrinker map, a new object might have been
+				 * added. To make sure, we have the bit set in this
+				 * case, we invoke the shrinker one more time and reset
+				 * the bit if it reports that it is not empty anymore.
+				 * The memory barrier here pairs with the barrier in
+				 * set_shrinker_bit():
+				 *
+				 * list_lru_add()     shrink_slab_memcg()
+				 *   list_add_tail()    clear_bit()
+				 *   <MB>               <MB>
+				 *   set_bit()          do_shrink_slab()
+				 */
+				smp_mb__after_atomic();
+				ret = do_shrink_slab(&sc, shrinker, priority);
+				if (ret == SHRINK_EMPTY)
+					ret = 0;
+				else
+					set_shrinker_bit(memcg, nid, shrinker_id);
+			}
+			freed += ret;
+			shrinker_put(shrinker);
+		}
+
+		index++;
+		goto again;
+	}
+unlock:
+	rcu_read_unlock();
+	return freed;
+}
+#else /* !CONFIG_MEMCG */
+static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
+			struct mem_cgroup *memcg, int priority)
+{
+	return 0;
+}
+#endif /* CONFIG_MEMCG */
+
+/**
+ * shrink_slab - shrink slab caches
+ * @gfp_mask: allocation context
+ * @nid: node whose slab caches to target
+ * @memcg: memory cgroup whose slab caches to target
+ * @priority: the reclaim priority
+ *
+ * Call the shrink functions to age shrinkable caches.
+ *
+ * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
+ * unaware shrinkers will receive a node id of 0 instead.
+ *
+ * @memcg specifies the memory cgroup to target. Unaware shrinkers
+ * are called only if it is the root cgroup.
+ *
+ * @priority is sc->priority, we take the number of objects and >> by priority
+ * in order to get the scan target.
+ *
+ * Returns the number of reclaimed slab objects.
+ */
+unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct mem_cgroup *memcg,
+			  int priority)
+{
+	unsigned long ret, freed = 0;
+	struct shrinker *shrinker;
+
+	/*
+	 * The root memcg might be allocated even though memcg is disabled
+	 * via "cgroup_disable=memory" boot parameter.  This could make
+	 * mem_cgroup_is_root() return false, then just run memcg slab
+	 * shrink, but skip global shrink.  This may result in premature
+	 * oom.
+	 */
+	if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
+		return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
+
+	/*
+	 * lockless algorithm of global shrink.
+	 *
+	 * In the unregistration setp, the shrinker will be freed asynchronously
+	 * via RCU after its refcount reaches 0. So both rcu_read_lock() and
+	 * shrinker_try_get() can be used to ensure the existence of the shrinker.
+	 *
+	 * So in the global shrink:
+	 *  step 1: use rcu_read_lock() to guarantee existence of the shrinker
+	 *          and the validity of the shrinker_list walk.
+	 *  step 2: use shrinker_try_get() to try get the refcount, if successful,
+	 *          then the existence of the shrinker can also be guaranteed,
+	 *          so we can release the RCU lock to do do_shrink_slab() that
+	 *          may sleep.
+	 *  step 3: *MUST* to reacquire the RCU lock before calling shrinker_put(),
+	 *          which ensures that neither this shrinker nor the next shrinker
+	 *          will be freed in the next traversal operation.
+	 *  step 4: do shrinker_put() paired with step 2 to put the refcount,
+	 *          if the refcount reaches 0, then wake up the waiter in
+	 *          shrinker_free() by calling complete().
+	 */
+	rcu_read_lock();
+	list_for_each_entry_rcu(shrinker, &shrinker_list, list) {
+		struct shrink_control sc = {
+			.gfp_mask = gfp_mask,
+			.nid = nid,
+			.memcg = memcg,
+		};
+
+		if (!shrinker_try_get(shrinker))
+			continue;
+
+		rcu_read_unlock();
+
+		ret = do_shrink_slab(&sc, shrinker, priority);
+		if (ret == SHRINK_EMPTY)
+			ret = 0;
+		freed += ret;
+
+		rcu_read_lock();
+		shrinker_put(shrinker);
+	}
+
+	rcu_read_unlock();
+	cond_resched();
+	return freed;
+}
+
+struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...)
+{
+	struct shrinker *shrinker;
+	unsigned int size;
+	va_list ap;
+	int err;
+
+	shrinker = kzalloc(sizeof(struct shrinker), GFP_KERNEL);
+	if (!shrinker)
+		return NULL;
+
+	va_start(ap, fmt);
+	err = shrinker_debugfs_name_alloc(shrinker, fmt, ap);
+	va_end(ap);
+	if (err)
+		goto err_name;
+
+	shrinker->flags = flags | SHRINKER_ALLOCATED;
+	shrinker->seeks = DEFAULT_SEEKS;
+
+	if (flags & SHRINKER_MEMCG_AWARE) {
+		err = shrinker_memcg_alloc(shrinker);
+		if (err == -ENOSYS) {
+			/* Memcg is not supported, fallback to non-memcg-aware shrinker. */
+			shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
+			goto non_memcg;
+		}
+
+		if (err)
+			goto err_flags;
+
+		return shrinker;
+	}
+
+non_memcg:
+	/*
+	 * The nr_deferred is available on per memcg level for memcg aware
+	 * shrinkers, so only allocate nr_deferred in the following cases:
+	 *  - non-memcg-aware shrinkers
+	 *  - !CONFIG_MEMCG
+	 *  - memcg is disabled by kernel command line
+	 */
+	size = sizeof(*shrinker->nr_deferred);
+	if (flags & SHRINKER_NUMA_AWARE)
+		size *= nr_node_ids;
+
+	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
+	if (!shrinker->nr_deferred)
+		goto err_flags;
+
+	return shrinker;
+
+err_flags:
+	shrinker_debugfs_name_free(shrinker);
+err_name:
+	kfree(shrinker);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(shrinker_alloc);
+
+void shrinker_register(struct shrinker *shrinker)
+{
+	if (unlikely(!(shrinker->flags & SHRINKER_ALLOCATED))) {
+		pr_warn("Must use shrinker_alloc() to dynamically allocate the shrinker");
+		return;
+	}
+
+	mutex_lock(&shrinker_mutex);
+	list_add_tail_rcu(&shrinker->list, &shrinker_list);
+	shrinker->flags |= SHRINKER_REGISTERED;
+	shrinker_debugfs_add(shrinker);
+	mutex_unlock(&shrinker_mutex);
+
+	init_completion(&shrinker->done);
+	/*
+	 * Now the shrinker is fully set up, take the first reference to it to
+	 * indicate that lookup operations are now allowed to use it via
+	 * shrinker_try_get().
+	 */
+	refcount_set(&shrinker->refcount, 1);
+}
+EXPORT_SYMBOL_GPL(shrinker_register);
+
+static void shrinker_free_rcu_cb(struct rcu_head *head)
+{
+	struct shrinker *shrinker = container_of(head, struct shrinker, rcu);
+
+	kfree(shrinker->nr_deferred);
+	kfree(shrinker);
+}
+
+void shrinker_free(struct shrinker *shrinker)
+{
+	struct dentry *debugfs_entry = NULL;
+	int debugfs_id;
+
+	if (!shrinker)
+		return;
+
+	if (shrinker->flags & SHRINKER_REGISTERED) {
+		/* drop the initial refcount */
+		shrinker_put(shrinker);
+		/*
+		 * Wait for all lookups of the shrinker to complete, after that,
+		 * no shrinker is running or will run again, then we can safely
+		 * free it asynchronously via RCU and safely free the structure
+		 * where the shrinker is located, such as super_block etc.
+		 */
+		wait_for_completion(&shrinker->done);
+	}
+
+	mutex_lock(&shrinker_mutex);
+	if (shrinker->flags & SHRINKER_REGISTERED) {
+		/*
+		 * Now we can safely remove it from the shrinker_list and then
+		 * free it.
+		 */
+		list_del_rcu(&shrinker->list);
+		debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
+		shrinker->flags &= ~SHRINKER_REGISTERED;
+	}
+
+	shrinker_debugfs_name_free(shrinker);
+
+	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
+		shrinker_memcg_remove(shrinker);
+	mutex_unlock(&shrinker_mutex);
+
+	if (debugfs_entry)
+		shrinker_debugfs_remove(debugfs_entry, debugfs_id);
+
+	call_rcu(&shrinker->rcu, shrinker_free_rcu_cb);
+}
+EXPORT_SYMBOL_GPL(shrinker_free);
author	Linus Torvalds <torvalds@linux-foundation.org>	2023-11-02 19:38:47 -1000
committer	Linus Torvalds <torvalds@linux-foundation.org>	2023-11-02 19:38:47 -1000
commit	ecae0bd5173b1014f95a14a8dfbe40ec10367dcf (patch)
tree	f571213ef1a35354ea79f0240a180fdb4111b290 /mm/shrinker.c
parent	bc3012f4e3a9765de81f454cb8f9bb16aafc6ff5 (diff)
parent	9732336006764e2ee61225387e3c70eae9139035 (diff)
download	lwn-ecae0bd5173b1014f95a14a8dfbe40ec10367dcf.tar.gz lwn-ecae0bd5173b1014f95a14a8dfbe40ec10367dcf.zip