budget.c

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/*
 * This file is part of UBIFS.
 *
 * Copyright (C) 2006-2008 Nokia Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * Authors: Adrian Hunter
 *          Artem Bityutskiy (Битюцкий Артём)
 */

/*
 * This file implements the budgeting sub-system which is responsible for UBIFS
 * space management.
 *
 * Factors such as compression, wasted space at the ends of LEBs, space in other
 * journal heads, the effect of updates on the index, and so on, make it
 * impossible to accurately predict the amount of space needed. Consequently
 * approximations are used.
 */

#include "ubifs.h"
#include <linux/writeback.h>
#include <linux/math64.h>

/*
 * When pessimistic budget calculations say that there is no enough space,
 * UBIFS starts writing back dirty inodes and pages, doing garbage collection,
 * or committing. The below constant defines maximum number of times UBIFS
 * repeats the operations.
 */
#define MAX_MKSPC_RETRIES 3

/*
 * The below constant defines amount of dirty pages which should be written
 * back at when trying to shrink the liability.
 */
#define NR_TO_WRITE 16

static void shrink_liability(struct ubifs_info *c, int nr_to_write)
{
    down_read(&c->vfs_sb->s_umount);
    writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);
    up_read(&c->vfs_sb->s_umount);
}

static int run_gc(struct ubifs_info *c)
{
    int err, lnum;

    /* Make some free space by garbage-collecting dirty space */
    down_read(&c->commit_sem);
    lnum = ubifs_garbage_collect(c, 1);
    up_read(&c->commit_sem);
    if (lnum < 0)
        return lnum;

    /* GC freed one LEB, return it to lprops */
    dbg_budg("GC freed LEB %d", lnum);
    err = ubifs_return_leb(c, lnum);
    if (err)
        return err;
    return 0;
}

static long long get_liability(struct ubifs_info *c)
{
    long long liab;

    spin_lock(&c->space_lock);
    liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;
    spin_unlock(&c->space_lock);
    return liab;
}

static int make_free_space(struct ubifs_info *c)
{
    int err, retries = 0;
    long long liab1, liab2;

    do {
        liab1 = get_liability(c);
        /*
         * We probably have some dirty pages or inodes (liability), try
         * to write them back.
         */
        dbg_budg("liability %lld, run write-back", liab1);
        shrink_liability(c, NR_TO_WRITE);

        liab2 = get_liability(c);
        if (liab2 < liab1)
            return -EAGAIN;

        dbg_budg("new liability %lld (not shrunk)", liab2);

        /* Liability did not shrink again, try GC */
        dbg_budg("Run GC");
        err = run_gc(c);
        if (!err)
            return -EAGAIN;

        if (err != -EAGAIN && err != -ENOSPC)
            /* Some real error happened */
            return err;

        dbg_budg("Run commit (retries %d)", retries);
        err = ubifs_run_commit(c);
        if (err)
            return err;
    } while (retries++ < MAX_MKSPC_RETRIES);

    return -ENOSPC;
}

int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
{
    int idx_lebs;
    long long idx_size;

    idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;
    /* And make sure we have thrice the index size of space reserved */
    idx_size += idx_size << 1;
    /*
     * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
     * pair, nor similarly the two variables for the new index size, so we
     * have to do this costly 64-bit division on fast-path.
     */
    idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);
    /*
     * The index head is not available for the in-the-gaps method, so add an
     * extra LEB to compensate.
     */
    idx_lebs += 1;
    if (idx_lebs < MIN_INDEX_LEBS)
        idx_lebs = MIN_INDEX_LEBS;
    return idx_lebs;
}

long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
{
    int subtract_lebs;
    long long available;

    available = c->main_bytes - c->lst.total_used;

    /*
     * Now 'available' contains theoretically available flash space
     * assuming there is no index, so we have to subtract the space which
     * is reserved for the index.
     */
    subtract_lebs = min_idx_lebs;

    /* Take into account that GC reserves one LEB for its own needs */
    subtract_lebs += 1;

    /*
     * The GC journal head LEB is not really accessible. And since
     * different write types go to different heads, we may count only on
     * one head's space.
     */
    subtract_lebs += c->jhead_cnt - 1;

    /* We also reserve one LEB for deletions, which bypass budgeting */
    subtract_lebs += 1;

    available -= (long long)subtract_lebs * c->leb_size;

    /* Subtract the dead space which is not available for use */
    available -= c->lst.total_dead;

    /*
     * Subtract dark space, which might or might not be usable - it depends
     * on the data which we have on the media and which will be written. If
     * this is a lot of uncompressed or not-compressible data, the dark
     * space cannot be used.
     */
    available -= c->lst.total_dark;

    /*
     * However, there is more dark space. The index may be bigger than
     * @min_idx_lebs. Those extra LEBs are assumed to be available, but
     * their dark space is not included in total_dark, so it is subtracted
     * here.
     */
    if (c->lst.idx_lebs > min_idx_lebs) {
        subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
        available -= subtract_lebs * c->dark_wm;
    }

    /* The calculations are rough and may end up with a negative number */
    return available > 0 ? available : 0;
}

static int can_use_rp(struct ubifs_info *c)
{
    if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
        (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
        return 1;
    return 0;
}

static int do_budget_space(struct ubifs_info *c)
{
    long long outstanding, available;
    int lebs, rsvd_idx_lebs, min_idx_lebs;

    /* First budget index space */
    min_idx_lebs = ubifs_calc_min_idx_lebs(c);

    /* Now 'min_idx_lebs' contains number of LEBs to reserve */
    if (min_idx_lebs > c->lst.idx_lebs)
        rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
    else
        rsvd_idx_lebs = 0;

    /*
     * The number of LEBs that are available to be used by the index is:
     *
     *    @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
     *    @c->lst.taken_empty_lebs
     *
     * @c->lst.empty_lebs are available because they are empty.
     * @c->freeable_cnt are available because they contain only free and
     * dirty space, @c->idx_gc_cnt are available because they are index
     * LEBs that have been garbage collected and are awaiting the commit
     * before they can be used. And the in-the-gaps method will grab these
     * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
     * already been allocated for some purpose.
     *
     * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
     * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
     * are taken until after the commit).
     *
     * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
     * because of the way we serialize LEB allocations and budgeting. See a
     * comment in 'ubifs_find_free_space()'.
     */
    lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
           c->lst.taken_empty_lebs;
    if (unlikely(rsvd_idx_lebs > lebs)) {
        dbg_budg("out of indexing space: min_idx_lebs %d (old %d), rsvd_idx_lebs %d",
             min_idx_lebs, c->bi.min_idx_lebs, rsvd_idx_lebs);
        return -ENOSPC;
    }

    available = ubifs_calc_available(c, min_idx_lebs);
    outstanding = c->bi.data_growth + c->bi.dd_growth;

    if (unlikely(available < outstanding)) {
        dbg_budg("out of data space: available %lld, outstanding %lld",
             available, outstanding);
        return -ENOSPC;
    }

    if (available - outstanding <= c->rp_size && !can_use_rp(c))
        return -ENOSPC;

    c->bi.min_idx_lebs = min_idx_lebs;
    return 0;
}

static int calc_idx_growth(const struct ubifs_info *c,
               const struct ubifs_budget_req *req)
{
    int znodes;

    znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
         req->new_dent;
    return znodes * c->max_idx_node_sz;
}

static int calc_data_growth(const struct ubifs_info *c,
                const struct ubifs_budget_req *req)
{
    int data_growth;

    data_growth = req->new_ino  ? c->bi.inode_budget : 0;
    if (req->new_page)
        data_growth += c->bi.page_budget;
    if (req->new_dent)
        data_growth += c->bi.dent_budget;
    data_growth += req->new_ino_d;
    return data_growth;
}

static int calc_dd_growth(const struct ubifs_info *c,
              const struct ubifs_budget_req *req)
{
    int dd_growth;

    dd_growth = req->dirtied_page ? c->bi.page_budget : 0;

    if (req->dirtied_ino)
        dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);
    if (req->mod_dent)
        dd_growth += c->bi.dent_budget;
    dd_growth += req->dirtied_ino_d;
    return dd_growth;
}

int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
{
    int uninitialized_var(cmt_retries), uninitialized_var(wb_retries);
    int err, idx_growth, data_growth, dd_growth, retried = 0;

    ubifs_assert(req->new_page <= 1);
    ubifs_assert(req->dirtied_page <= 1);
    ubifs_assert(req->new_dent <= 1);
    ubifs_assert(req->mod_dent <= 1);
    ubifs_assert(req->new_ino <= 1);
    ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
    ubifs_assert(req->dirtied_ino <= 4);
    ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
    ubifs_assert(!(req->new_ino_d & 7));
    ubifs_assert(!(req->dirtied_ino_d & 7));

    data_growth = calc_data_growth(c, req);
    dd_growth = calc_dd_growth(c, req);
    if (!data_growth && !dd_growth)
        return 0;
    idx_growth = calc_idx_growth(c, req);

again:
    spin_lock(&c->space_lock);
    ubifs_assert(c->bi.idx_growth >= 0);
    ubifs_assert(c->bi.data_growth >= 0);
    ubifs_assert(c->bi.dd_growth >= 0);

    if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {
        dbg_budg("no space");
        spin_unlock(&c->space_lock);
        return -ENOSPC;
    }

    c->bi.idx_growth += idx_growth;
    c->bi.data_growth += data_growth;
    c->bi.dd_growth += dd_growth;

    err = do_budget_space(c);
    if (likely(!err)) {
        req->idx_growth = idx_growth;
        req->data_growth = data_growth;
        req->dd_growth = dd_growth;
        spin_unlock(&c->space_lock);
        return 0;
    }

    /* Restore the old values */
    c->bi.idx_growth -= idx_growth;
    c->bi.data_growth -= data_growth;
    c->bi.dd_growth -= dd_growth;
    spin_unlock(&c->space_lock);

    if (req->fast) {
        dbg_budg("no space for fast budgeting");
        return err;
    }

    err = make_free_space(c);
    cond_resched();
    if (err == -EAGAIN) {
        dbg_budg("try again");
        goto again;
    } else if (err == -ENOSPC) {
        if (!retried) {
            retried = 1;
            dbg_budg("-ENOSPC, but anyway try once again");
            goto again;
        }
        dbg_budg("FS is full, -ENOSPC");
        c->bi.nospace = 1;
        if (can_use_rp(c) || c->rp_size == 0)
            c->bi.nospace_rp = 1;
        smp_wmb();
    } else
        ubifs_err("cannot budget space, error %d", err);
    return err;
}

void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
{
    ubifs_assert(req->new_page <= 1);
    ubifs_assert(req->dirtied_page <= 1);
    ubifs_assert(req->new_dent <= 1);
    ubifs_assert(req->mod_dent <= 1);
    ubifs_assert(req->new_ino <= 1);
    ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);
    ubifs_assert(req->dirtied_ino <= 4);
    ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);
    ubifs_assert(!(req->new_ino_d & 7));
    ubifs_assert(!(req->dirtied_ino_d & 7));
    if (!req->recalculate) {
        ubifs_assert(req->idx_growth >= 0);
        ubifs_assert(req->data_growth >= 0);
        ubifs_assert(req->dd_growth >= 0);
    }

    if (req->recalculate) {
        req->data_growth = calc_data_growth(c, req);
        req->dd_growth = calc_dd_growth(c, req);
        req->idx_growth = calc_idx_growth(c, req);
    }

    if (!req->data_growth && !req->dd_growth)
        return;

    c->bi.nospace = c->bi.nospace_rp = 0;
    smp_wmb();

    spin_lock(&c->space_lock);
    c->bi.idx_growth -= req->idx_growth;
    c->bi.uncommitted_idx += req->idx_growth;
    c->bi.data_growth -= req->data_growth;
    c->bi.dd_growth -= req->dd_growth;
    c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);

    ubifs_assert(c->bi.idx_growth >= 0);
    ubifs_assert(c->bi.data_growth >= 0);
    ubifs_assert(c->bi.dd_growth >= 0);
    ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
    ubifs_assert(!(c->bi.idx_growth & 7));
    ubifs_assert(!(c->bi.data_growth & 7));
    ubifs_assert(!(c->bi.dd_growth & 7));
    spin_unlock(&c->space_lock);
}

void ubifs_convert_page_budget(struct ubifs_info *c)
{
    spin_lock(&c->space_lock);
    /* Release the index growth reservation */
    c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;
    /* Release the data growth reservation */
    c->bi.data_growth -= c->bi.page_budget;
    /* Increase the dirty data growth reservation instead */
    c->bi.dd_growth += c->bi.page_budget;
    /* And re-calculate the indexing space reservation */
    c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
    spin_unlock(&c->space_lock);
}

void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
                      struct ubifs_inode *ui)
{
    struct ubifs_budget_req req;

    memset(&req, 0, sizeof(struct ubifs_budget_req));
    /* The "no space" flags will be cleared because dd_growth is > 0 */
    req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);
    ubifs_release_budget(c, &req);
}

long long ubifs_reported_space(const struct ubifs_info *c, long long free)
{
    int divisor, factor, f;

    /*
     * Reported space size is @free * X, where X is UBIFS block size
     * divided by UBIFS block size + all overhead one data block
     * introduces. The overhead is the node header + indexing overhead.
     *
     * Indexing overhead calculations are based on the following formula:
     * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
     * of data nodes, f - fanout. Because effective UBIFS fanout is twice
     * as less than maximum fanout, we assume that each data node
     * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
     * Note, the multiplier 3 is because UBIFS reserves thrice as more space
     * for the index.
     */
    f = c->fanout > 3 ? c->fanout >> 1 : 2;
    factor = UBIFS_BLOCK_SIZE;
    divisor = UBIFS_MAX_DATA_NODE_SZ;
    divisor += (c->max_idx_node_sz * 3) / (f - 1);
    free *= factor;
    return div_u64(free, divisor);
}

long long ubifs_get_free_space_nolock(struct ubifs_info *c)
{
    int rsvd_idx_lebs, lebs;
    long long available, outstanding, free;

    ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
    outstanding = c->bi.data_growth + c->bi.dd_growth;
    available = ubifs_calc_available(c, c->bi.min_idx_lebs);

    /*
     * When reporting free space to user-space, UBIFS guarantees that it is
     * possible to write a file of free space size. This means that for
     * empty LEBs we may use more precise calculations than
     * 'ubifs_calc_available()' is using. Namely, we know that in empty
     * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
     * Thus, amend the available space.
     *
     * Note, the calculations below are similar to what we have in
     * 'do_budget_space()', so refer there for comments.
     */
    if (c->bi.min_idx_lebs > c->lst.idx_lebs)
        rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;
    else
        rsvd_idx_lebs = 0;
    lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
           c->lst.taken_empty_lebs;
    lebs -= rsvd_idx_lebs;
    available += lebs * (c->dark_wm - c->leb_overhead);

    if (available > outstanding)
        free = ubifs_reported_space(c, available - outstanding);
    else
        free = 0;
    return free;
}

long long ubifs_get_free_space(struct ubifs_info *c)
{
    long long free;

    spin_lock(&c->space_lock);
    free = ubifs_get_free_space_nolock(c);
    spin_unlock(&c->space_lock);

    return free;
}