// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2018 HUAWEI, Inc.
 *             https://www.huawei.com/
 * Copyright (C) 2024 Alibaba Cloud
 */
#include "internal.h"

struct z_erofs_gbuf {
        spinlock_t lock;
        void *ptr;
        struct page **pages;
        unsigned int nrpages;
};

static struct z_erofs_gbuf *z_erofs_gbufpool, *z_erofs_rsvbuf;
static unsigned int z_erofs_gbuf_count, z_erofs_gbuf_nrpages,
                z_erofs_rsv_nrpages;

module_param_named(global_buffers, z_erofs_gbuf_count, uint, 0444);
module_param_named(reserved_pages, z_erofs_rsv_nrpages, uint, 0444);

atomic_long_t erofs_global_shrink_cnt;  /* for all mounted instances */

/* protects `erofs_sb_list_lock` and the mounted `erofs_sb_list` */
static DEFINE_SPINLOCK(erofs_sb_list_lock);
static LIST_HEAD(erofs_sb_list);
static unsigned int shrinker_run_no;
static struct shrinker *erofs_shrinker_info;

static unsigned int z_erofs_gbuf_id(void)
{
        return raw_smp_processor_id() % z_erofs_gbuf_count;
}

void *z_erofs_get_gbuf(unsigned int requiredpages)
        __acquires(gbuf->lock)
{
        struct z_erofs_gbuf *gbuf;

        migrate_disable();
        gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
        spin_lock(&gbuf->lock);
        /* check if the buffer is too small */
        if (requiredpages > gbuf->nrpages) {
                spin_unlock(&gbuf->lock);
                migrate_enable();
                /* (for sparse checker) pretend gbuf->lock is still taken */
                __acquire(gbuf->lock);
                return NULL;
        }
        return gbuf->ptr;
}

void z_erofs_put_gbuf(void *ptr) __releases(gbuf->lock)
{
        struct z_erofs_gbuf *gbuf;

        gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
        DBG_BUGON(gbuf->ptr != ptr);
        spin_unlock(&gbuf->lock);
        migrate_enable();
}

int z_erofs_gbuf_growsize(unsigned int nrpages)
{
        static DEFINE_MUTEX(gbuf_resize_mutex);
        struct page **tmp_pages = NULL;
        struct z_erofs_gbuf *gbuf;
        void *ptr, *old_ptr;
        int last, i, j;

        mutex_lock(&gbuf_resize_mutex);
        /* avoid shrinking gbufs, since no idea how many fses rely on */
        if (nrpages <= z_erofs_gbuf_nrpages) {
                mutex_unlock(&gbuf_resize_mutex);
                return 0;
        }

        for (i = 0; i < z_erofs_gbuf_count; ++i) {
                gbuf = &z_erofs_gbufpool[i];
                tmp_pages = kzalloc_objs(*tmp_pages, nrpages);
                if (!tmp_pages)
                        goto out;

                for (j = 0; j < gbuf->nrpages; ++j)
                        tmp_pages[j] = gbuf->pages[j];
                do {
                        last = j;
                        j = alloc_pages_bulk(GFP_KERNEL, nrpages,
                                             tmp_pages);
                        if (last == j)
                                goto out;
                } while (j != nrpages);

                ptr = vmap(tmp_pages, nrpages, VM_MAP, PAGE_KERNEL);
                if (!ptr)
                        goto out;

                spin_lock(&gbuf->lock);
                kfree(gbuf->pages);
                gbuf->pages = tmp_pages;
                old_ptr = gbuf->ptr;
                gbuf->ptr = ptr;
                gbuf->nrpages = nrpages;
                spin_unlock(&gbuf->lock);
                if (old_ptr)
                        vunmap(old_ptr);
        }
        z_erofs_gbuf_nrpages = nrpages;
out:
        if (i < z_erofs_gbuf_count && tmp_pages) {
                for (j = 0; j < nrpages; ++j)
                        if (tmp_pages[j] && (j >= gbuf->nrpages ||
                                             tmp_pages[j] != gbuf->pages[j]))
                                __free_page(tmp_pages[j]);
                kfree(tmp_pages);
        }
        mutex_unlock(&gbuf_resize_mutex);
        return i < z_erofs_gbuf_count ? -ENOMEM : 0;
}

int __init z_erofs_gbuf_init(void)
{
        unsigned int i, total = num_possible_cpus();

        if (z_erofs_gbuf_count)
                total = min(z_erofs_gbuf_count, total);
        z_erofs_gbuf_count = total;

        /* The last (special) global buffer is the reserved buffer */
        total += !!z_erofs_rsv_nrpages;

        z_erofs_gbufpool = kzalloc_objs(*z_erofs_gbufpool, total);
        if (!z_erofs_gbufpool)
                return -ENOMEM;

        if (z_erofs_rsv_nrpages) {
                z_erofs_rsvbuf = &z_erofs_gbufpool[total - 1];
                z_erofs_rsvbuf->pages = kzalloc_objs(*z_erofs_rsvbuf->pages,
                                                     z_erofs_rsv_nrpages);
                if (!z_erofs_rsvbuf->pages) {
                        z_erofs_rsvbuf = NULL;
                        z_erofs_rsv_nrpages = 0;
                }
        }
        for (i = 0; i < total; ++i)
                spin_lock_init(&z_erofs_gbufpool[i].lock);
        return 0;
}

void z_erofs_gbuf_exit(void)
{
        int i, j;

        for (i = 0; i < z_erofs_gbuf_count + (!!z_erofs_rsvbuf); ++i) {
                struct z_erofs_gbuf *gbuf = &z_erofs_gbufpool[i];

                if (gbuf->ptr) {
                        vunmap(gbuf->ptr);
                        gbuf->ptr = NULL;
                }

                if (!gbuf->pages)
                        continue;

                for (j = 0; j < gbuf->nrpages; ++j)
                        if (gbuf->pages[j])
                                put_page(gbuf->pages[j]);
                kfree(gbuf->pages);
                gbuf->pages = NULL;
        }
        kfree(z_erofs_gbufpool);
}

struct page *__erofs_allocpage(struct page **pagepool, gfp_t gfp, bool tryrsv)
{
        struct page *page = *pagepool;

        if (page) {
                *pagepool = (struct page *)page_private(page);
        } else if (tryrsv && z_erofs_rsvbuf && z_erofs_rsvbuf->nrpages) {
                spin_lock(&z_erofs_rsvbuf->lock);
                if (z_erofs_rsvbuf->nrpages)
                        page = z_erofs_rsvbuf->pages[--z_erofs_rsvbuf->nrpages];
                spin_unlock(&z_erofs_rsvbuf->lock);
        }
        if (!page)
                page = alloc_page(gfp);
        DBG_BUGON(page && page_ref_count(page) != 1);
        return page;
}

void erofs_release_pages(struct page **pagepool)
{
        while (*pagepool) {
                struct page *page = *pagepool;

                *pagepool = (struct page *)page_private(page);
                /* try to fill reserved global pool first */
                if (z_erofs_rsvbuf && z_erofs_rsvbuf->nrpages <
                                z_erofs_rsv_nrpages) {
                        spin_lock(&z_erofs_rsvbuf->lock);
                        if (z_erofs_rsvbuf->nrpages < z_erofs_rsv_nrpages) {
                                z_erofs_rsvbuf->pages[z_erofs_rsvbuf->nrpages++]
                                                = page;
                                spin_unlock(&z_erofs_rsvbuf->lock);
                                continue;
                        }
                        spin_unlock(&z_erofs_rsvbuf->lock);
                }
                put_page(page);
        }
}

void erofs_shrinker_register(struct super_block *sb)
{
        struct erofs_sb_info *sbi = EROFS_SB(sb);

        mutex_init(&sbi->umount_mutex);

        spin_lock(&erofs_sb_list_lock);
        list_add(&sbi->list, &erofs_sb_list);
        spin_unlock(&erofs_sb_list_lock);
}

void erofs_shrinker_unregister(struct super_block *sb)
{
        struct erofs_sb_info *const sbi = EROFS_SB(sb);

        mutex_lock(&sbi->umount_mutex);
        while (!xa_empty(&sbi->managed_pslots)) {
                z_erofs_shrink_scan(sbi, ~0UL);
                cond_resched();
        }
        spin_lock(&erofs_sb_list_lock);
        list_del(&sbi->list);
        spin_unlock(&erofs_sb_list_lock);
        mutex_unlock(&sbi->umount_mutex);
}

static unsigned long erofs_shrink_count(struct shrinker *shrink,
                                        struct shrink_control *sc)
{
        return atomic_long_read(&erofs_global_shrink_cnt) ?: SHRINK_EMPTY;
}

static unsigned long erofs_shrink_scan(struct shrinker *shrink,
                                       struct shrink_control *sc)
{
        struct erofs_sb_info *sbi;
        struct list_head *p;

        unsigned long nr = sc->nr_to_scan;
        unsigned int run_no;
        unsigned long freed = 0;

        spin_lock(&erofs_sb_list_lock);
        do {
                run_no = ++shrinker_run_no;
        } while (run_no == 0);

        /* Iterate over all mounted superblocks and try to shrink them */
        p = erofs_sb_list.next;
        while (p != &erofs_sb_list) {
                sbi = list_entry(p, struct erofs_sb_info, list);

                /*
                 * We move the ones we do to the end of the list, so we stop
                 * when we see one we have already done.
                 */
                if (sbi->shrinker_run_no == run_no)
                        break;

                if (!mutex_trylock(&sbi->umount_mutex)) {
                        p = p->next;
                        continue;
                }

                spin_unlock(&erofs_sb_list_lock);
                sbi->shrinker_run_no = run_no;
                freed += z_erofs_shrink_scan(sbi, nr - freed);
                spin_lock(&erofs_sb_list_lock);
                /* Get the next list element before we move this one */
                p = p->next;

                /*
                 * Move this one to the end of the list to provide some
                 * fairness.
                 */
                list_move_tail(&sbi->list, &erofs_sb_list);
                mutex_unlock(&sbi->umount_mutex);

                if (freed >= nr)
                        break;
        }
        spin_unlock(&erofs_sb_list_lock);
        return freed;
}

int __init erofs_init_shrinker(void)
{
        erofs_shrinker_info = shrinker_alloc(0, "erofs-shrinker");
        if (!erofs_shrinker_info)
                return -ENOMEM;

        erofs_shrinker_info->count_objects = erofs_shrink_count;
        erofs_shrinker_info->scan_objects = erofs_shrink_scan;
        shrinker_register(erofs_shrinker_info);
        return 0;
}

void erofs_exit_shrinker(void)
{
        shrinker_free(erofs_shrinker_info);
}