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    Subject[PATCH v2 5/8] ext4: Abstract out overlap fix/check logic in ext4_mb_normalize_request()
    Date
    Abstract out the logic of fixing PA overlaps in ext4_mb_normalize_request to
    improve readability of code. This also makes it easier to make changes
    to the overlap logic in future.

    There are no functional changes in this patch

    Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
    Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    ---
    fs/ext4/mballoc.c | 110 +++++++++++++++++++++++++++++-----------------
    1 file changed, 69 insertions(+), 41 deletions(-)

    diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
    index 210f90a6229a..a76fc19ed8d5 100644
    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -4007,6 +4007,74 @@ ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
    rcu_read_unlock();
    }

    +/*
    + * Given an allocation context "ac" and a range "start", "end", check
    + * and adjust boundaries if the range overlaps with any of the existing
    + * preallocatoins stored in the corresponding inode of the allocation context.
    + *
    + *Parameters:
    + * ac allocation context
    + * start start of the new range
    + * end end of the new range
    + */
    +static inline void
    +ext4_mb_pa_adjust_overlap(struct ext4_allocation_context *ac,
    + ext4_lblk_t *start, ext4_lblk_t *end)
    +{
    + struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
    + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    + struct ext4_prealloc_space *tmp_pa;
    + ext4_lblk_t new_start, new_end;
    + ext4_lblk_t tmp_pa_start, tmp_pa_end;
    +
    + new_start = *start;
    + new_end = *end;
    +
    + /* check we don't cross already preallocated blocks */
    + rcu_read_lock();
    + list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
    + if (tmp_pa->pa_deleted)
    + continue;
    + spin_lock(&tmp_pa->pa_lock);
    + if (tmp_pa->pa_deleted) {
    + spin_unlock(&tmp_pa->pa_lock);
    + continue;
    + }
    +
    + tmp_pa_start = tmp_pa->pa_lstart;
    + tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
    +
    + /* PA must not overlap original request */
    + BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
    + ac->ac_o_ex.fe_logical < tmp_pa_start));
    +
    + /* skip PAs this normalized request doesn't overlap with */
    + if (tmp_pa_start >= new_end || tmp_pa_end <= new_start) {
    + spin_unlock(&tmp_pa->pa_lock);
    + continue;
    + }
    + BUG_ON(tmp_pa_start <= new_start && tmp_pa_end >= new_end);
    +
    + /* adjust start or end to be adjacent to this pa */
    + if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
    + BUG_ON(tmp_pa_end < new_start);
    + new_start = tmp_pa_end;
    + } else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
    + BUG_ON(tmp_pa_start > new_end);
    + new_end = tmp_pa_start;
    + }
    + spin_unlock(&tmp_pa->pa_lock);
    + }
    + rcu_read_unlock();
    +
    + /* XXX: extra loop to check we really don't overlap preallocations */
    + ext4_mb_pa_assert_overlap(ac, new_start, new_end);
    +
    + *start = new_start;
    + *end = new_end;
    + return;
    +}
    +
    /*
    * Normalization means making request better in terms of
    * size and alignment
    @@ -4021,9 +4089,6 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
    loff_t size, start_off;
    loff_t orig_size __maybe_unused;
    ext4_lblk_t start;
    - struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
    - struct ext4_prealloc_space *tmp_pa;
    - ext4_lblk_t tmp_pa_start, tmp_pa_end;

    /* do normalize only data requests, metadata requests
    do not need preallocation */
    @@ -4124,47 +4189,10 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,

    end = start + size;

    - /* check we don't cross already preallocated blocks */
    - rcu_read_lock();
    - list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
    - if (tmp_pa->pa_deleted)
    - continue;
    - spin_lock(&tmp_pa->pa_lock);
    - if (tmp_pa->pa_deleted) {
    - spin_unlock(&tmp_pa->pa_lock);
    - continue;
    - }
    -
    - tmp_pa_start = tmp_pa->pa_lstart;
    - tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
    -
    - /* PA must not overlap original request */
    - BUG_ON(!(ac->ac_o_ex.fe_logical >= tmp_pa_end ||
    - ac->ac_o_ex.fe_logical < tmp_pa_start));
    -
    - /* skip PAs this normalized request doesn't overlap with */
    - if (tmp_pa_start >= end || tmp_pa_end <= start) {
    - spin_unlock(&tmp_pa->pa_lock);
    - continue;
    - }
    - BUG_ON(tmp_pa_start <= start && tmp_pa_end >= end);
    + ext4_mb_pa_adjust_overlap(ac, &start, &end);

    - /* adjust start or end to be adjacent to this pa */
    - if (tmp_pa_end <= ac->ac_o_ex.fe_logical) {
    - BUG_ON(tmp_pa_end < start);
    - start = tmp_pa_end;
    - } else if (tmp_pa_start > ac->ac_o_ex.fe_logical) {
    - BUG_ON(tmp_pa_start > end);
    - end = tmp_pa_start;
    - }
    - spin_unlock(&tmp_pa->pa_lock);
    - }
    - rcu_read_unlock();
    size = end - start;

    - /* XXX: extra loop to check we really don't overlap preallocations */
    - ext4_mb_pa_assert_overlap(ac, start, end);
    -
    /*
    * In this function "start" and "size" are normalized for better
    * alignment and length such that we could preallocate more blocks.
    --
    2.31.1
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