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![Gao Xiang](/assets/img/avatar_default.png)
Let's avoid the current handcrafted lockref although `struct lockref` inclusion usually increases extra 4 bytes with an explicit spinlock if CONFIG_DEBUG_SPINLOCK is off. Apart from the size difference, note that the meaning of refcount is also changed to active users. IOWs, it doesn't take an extra refcount for XArray tree insertion. I don't observe any significant performance difference at least on our cloud compute server but the new one indeed simplifies the overall codebase a bit. Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> Reviewed-by: Yue Hu <huyue2@coolpad.com> Link: https://lore.kernel.org/r/20230529123727.79943-1-hsiangkao@linux.alibaba.com
288 lines
6.6 KiB
C
288 lines
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2018 HUAWEI, Inc.
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* https://www.huawei.com/
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*/
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#include "internal.h"
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struct page *erofs_allocpage(struct page **pagepool, gfp_t gfp)
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{
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struct page *page = *pagepool;
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if (page) {
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DBG_BUGON(page_ref_count(page) != 1);
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*pagepool = (struct page *)page_private(page);
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} else {
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page = alloc_page(gfp);
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}
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return page;
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}
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void erofs_release_pages(struct page **pagepool)
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{
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while (*pagepool) {
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struct page *page = *pagepool;
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*pagepool = (struct page *)page_private(page);
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put_page(page);
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}
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}
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#ifdef CONFIG_EROFS_FS_ZIP
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/* global shrink count (for all mounted EROFS instances) */
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static atomic_long_t erofs_global_shrink_cnt;
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static bool erofs_workgroup_get(struct erofs_workgroup *grp)
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{
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if (lockref_get_not_zero(&grp->lockref))
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return true;
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spin_lock(&grp->lockref.lock);
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if (__lockref_is_dead(&grp->lockref)) {
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spin_unlock(&grp->lockref.lock);
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return false;
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}
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if (!grp->lockref.count++)
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atomic_long_dec(&erofs_global_shrink_cnt);
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spin_unlock(&grp->lockref.lock);
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return true;
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}
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struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
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pgoff_t index)
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{
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struct erofs_sb_info *sbi = EROFS_SB(sb);
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struct erofs_workgroup *grp;
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repeat:
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rcu_read_lock();
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grp = xa_load(&sbi->managed_pslots, index);
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if (grp) {
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if (!erofs_workgroup_get(grp)) {
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/* prefer to relax rcu read side */
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rcu_read_unlock();
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goto repeat;
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}
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DBG_BUGON(index != grp->index);
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}
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rcu_read_unlock();
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return grp;
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}
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struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb,
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struct erofs_workgroup *grp)
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{
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struct erofs_sb_info *const sbi = EROFS_SB(sb);
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struct erofs_workgroup *pre;
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/*
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* Bump up before making this visible to others for the XArray in order
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* to avoid potential UAF without serialized by xa_lock.
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*/
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lockref_get(&grp->lockref);
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repeat:
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xa_lock(&sbi->managed_pslots);
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pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
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NULL, grp, GFP_NOFS);
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if (pre) {
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if (xa_is_err(pre)) {
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pre = ERR_PTR(xa_err(pre));
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} else if (!erofs_workgroup_get(pre)) {
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/* try to legitimize the current in-tree one */
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xa_unlock(&sbi->managed_pslots);
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cond_resched();
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goto repeat;
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}
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lockref_put_return(&grp->lockref);
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grp = pre;
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}
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xa_unlock(&sbi->managed_pslots);
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return grp;
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}
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static void __erofs_workgroup_free(struct erofs_workgroup *grp)
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{
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atomic_long_dec(&erofs_global_shrink_cnt);
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erofs_workgroup_free_rcu(grp);
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}
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void erofs_workgroup_put(struct erofs_workgroup *grp)
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{
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if (lockref_put_or_lock(&grp->lockref))
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return;
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DBG_BUGON(__lockref_is_dead(&grp->lockref));
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if (grp->lockref.count == 1)
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atomic_long_inc(&erofs_global_shrink_cnt);
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--grp->lockref.count;
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spin_unlock(&grp->lockref.lock);
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}
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static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
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struct erofs_workgroup *grp)
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{
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int free = false;
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spin_lock(&grp->lockref.lock);
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if (grp->lockref.count)
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goto out;
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/*
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* Note that all cached pages should be detached before deleted from
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* the XArray. Otherwise some cached pages could be still attached to
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* the orphan old workgroup when the new one is available in the tree.
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*/
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if (erofs_try_to_free_all_cached_pages(sbi, grp))
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goto out;
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/*
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* It's impossible to fail after the workgroup is freezed,
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* however in order to avoid some race conditions, add a
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* DBG_BUGON to observe this in advance.
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*/
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DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);
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lockref_mark_dead(&grp->lockref);
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free = true;
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out:
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spin_unlock(&grp->lockref.lock);
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if (free)
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__erofs_workgroup_free(grp);
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return free;
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}
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static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
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unsigned long nr_shrink)
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{
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struct erofs_workgroup *grp;
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unsigned int freed = 0;
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unsigned long index;
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xa_lock(&sbi->managed_pslots);
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xa_for_each(&sbi->managed_pslots, index, grp) {
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/* try to shrink each valid workgroup */
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if (!erofs_try_to_release_workgroup(sbi, grp))
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continue;
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xa_unlock(&sbi->managed_pslots);
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++freed;
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if (!--nr_shrink)
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return freed;
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xa_lock(&sbi->managed_pslots);
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}
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xa_unlock(&sbi->managed_pslots);
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return freed;
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}
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/* protected by 'erofs_sb_list_lock' */
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static unsigned int shrinker_run_no;
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/* protects the mounted 'erofs_sb_list' */
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static DEFINE_SPINLOCK(erofs_sb_list_lock);
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static LIST_HEAD(erofs_sb_list);
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void erofs_shrinker_register(struct super_block *sb)
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{
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struct erofs_sb_info *sbi = EROFS_SB(sb);
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mutex_init(&sbi->umount_mutex);
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spin_lock(&erofs_sb_list_lock);
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list_add(&sbi->list, &erofs_sb_list);
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spin_unlock(&erofs_sb_list_lock);
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}
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void erofs_shrinker_unregister(struct super_block *sb)
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{
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struct erofs_sb_info *const sbi = EROFS_SB(sb);
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mutex_lock(&sbi->umount_mutex);
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/* clean up all remaining workgroups in memory */
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erofs_shrink_workstation(sbi, ~0UL);
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spin_lock(&erofs_sb_list_lock);
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list_del(&sbi->list);
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spin_unlock(&erofs_sb_list_lock);
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mutex_unlock(&sbi->umount_mutex);
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}
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static unsigned long erofs_shrink_count(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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return atomic_long_read(&erofs_global_shrink_cnt);
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}
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static unsigned long erofs_shrink_scan(struct shrinker *shrink,
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struct shrink_control *sc)
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{
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struct erofs_sb_info *sbi;
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struct list_head *p;
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unsigned long nr = sc->nr_to_scan;
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unsigned int run_no;
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unsigned long freed = 0;
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spin_lock(&erofs_sb_list_lock);
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do {
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run_no = ++shrinker_run_no;
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} while (run_no == 0);
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/* Iterate over all mounted superblocks and try to shrink them */
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p = erofs_sb_list.next;
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while (p != &erofs_sb_list) {
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sbi = list_entry(p, struct erofs_sb_info, list);
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/*
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* We move the ones we do to the end of the list, so we stop
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* when we see one we have already done.
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*/
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if (sbi->shrinker_run_no == run_no)
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break;
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if (!mutex_trylock(&sbi->umount_mutex)) {
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p = p->next;
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continue;
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}
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spin_unlock(&erofs_sb_list_lock);
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sbi->shrinker_run_no = run_no;
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freed += erofs_shrink_workstation(sbi, nr - freed);
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spin_lock(&erofs_sb_list_lock);
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/* Get the next list element before we move this one */
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p = p->next;
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/*
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* Move this one to the end of the list to provide some
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* fairness.
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*/
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list_move_tail(&sbi->list, &erofs_sb_list);
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mutex_unlock(&sbi->umount_mutex);
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if (freed >= nr)
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break;
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}
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spin_unlock(&erofs_sb_list_lock);
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return freed;
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}
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static struct shrinker erofs_shrinker_info = {
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.scan_objects = erofs_shrink_scan,
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.count_objects = erofs_shrink_count,
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.seeks = DEFAULT_SEEKS,
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};
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int __init erofs_init_shrinker(void)
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{
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return register_shrinker(&erofs_shrinker_info, "erofs-shrinker");
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}
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void erofs_exit_shrinker(void)
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{
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unregister_shrinker(&erofs_shrinker_info);
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}
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#endif /* !CONFIG_EROFS_FS_ZIP */
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