Hi,
On 12/16, Gao Xiang wrote:
> get_new_segment is too unclear to understand how it works.
> This patch refactor it in a straight-forward way and
> I think it is equal to the original one.
Thank you for the work, however, unless we found any bug, I don't think we have
to just refactor the long-lived existing codes.
Thanks,
>
> This patch also fixes two issues in the original get_new_segment:
> 1) left_start could be overflowed when hint == 0 at first:
> ...
> } else {
> go_left = 1;
> * left_start = hint - 1;
> }
> ...
> * while (test_bit(left_start, free_i->free_secmap)) {
> 2) It will do find_next_zero_bit again when go_left == true and ALLOC_LEFT:
> ...
> find_other_zone:
> * secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
> if (secno >= MAIN_SECS(sbi)) {
> if (dir == ALLOC_RIGHT) {
> ...
> } else {
> go_left = 1;
> ...
> }
> }
> if (go_left == 0)
> goto skip_left;
> ...
> if (i < NR_CURSEG_TYPE) {
> /* zone is in user, try another */
> * if (go_left)
> * hint = zoneno * sbi->secs_per_zone - 1;
> ...
> init = false;
> goto find_other_zone;
> }
>
> Signed-off-by: Gao Xiang <hsiangkao@xxxxxxx>
> ---
> fs/f2fs/segment.c | 137 ++++++++++++++++++++++++++++++++----------------------
> 1 file changed, 81 insertions(+), 56 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index c117e09..eea9d3f 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2047,82 +2047,107 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
> unsigned int *newseg, bool new_sec, int dir)
> {
> struct free_segmap_info *free_i = FREE_I(sbi);
> - unsigned int segno, secno, zoneno;
> + unsigned int segno = *newseg, zoneno;
> + unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
> unsigned int total_zones = MAIN_SECS(sbi) / sbi->secs_per_zone;
> - unsigned int hint = GET_SEC_FROM_SEG(sbi, *newseg);
> - unsigned int old_zoneno = GET_ZONE_FROM_SEG(sbi, *newseg);
> - unsigned int left_start = hint;
> - bool init = true;
> - int go_left = 0;
> + unsigned int old_zoneno = GET_ZONE_FROM_SEC(sbi, secno);
> + bool may_again = true, actually_go_left = false;
> int i;
>
> spin_lock(&free_i->segmap_lock);
>
> - if (!new_sec && ((*newseg + 1) % sbi->segs_per_sec)) {
> + /* first, attempt to find a segment in the current section */
> + if (!new_sec && ((segno + 1) % sbi->segs_per_sec)) {
> + unsigned end_segno = GET_SEG_FROM_SEC(sbi, secno + 1);
> +
> segno = find_next_zero_bit(free_i->free_segmap,
> - GET_SEG_FROM_SEC(sbi, hint + 1), *newseg + 1);
> - if (segno < GET_SEG_FROM_SEC(sbi, hint + 1))
> - goto got_it;
> + end_segno, segno + 1);
> +
> + if (segno < end_segno)
> + goto out;
> }
> -find_other_zone:
> - secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
> - if (secno >= MAIN_SECS(sbi)) {
> - if (dir == ALLOC_RIGHT) {
> - secno = find_next_zero_bit(free_i->free_secmap,
> - MAIN_SECS(sbi), 0);
> - f2fs_bug_on(sbi, secno >= MAIN_SECS(sbi));
> - } else {
> - go_left = 1;
> - left_start = hint - 1;
> +
> +try_another_section:
> + if (likely(!actually_go_left)) {
> + /*
> + * since ALLOC_LEFT takes much effort,
> + * prefer to ALLOC_RIGHT first
> + */
> + unsigned int new_secno = find_next_zero_bit(
> + free_i->free_secmap, MAIN_SECS(sbi), secno);
> +
> + if (new_secno < MAIN_SECS(sbi)) {
> + secno = new_secno;
> + goto check_another_zone;
> }
> }
> - if (go_left == 0)
> - goto skip_left;
>
> - while (test_bit(left_start, free_i->free_secmap)) {
> - if (left_start > 0) {
> - left_start--;
> - continue;
> - }
> - left_start = find_next_zero_bit(free_i->free_secmap,
> - MAIN_SECS(sbi), 0);
> - f2fs_bug_on(sbi, left_start >= MAIN_SECS(sbi));
> - break;
> + if (dir == ALLOC_LEFT) {
> + /* ALLOC_LEFT, no free sections on the right side */
> + actually_go_left = true;
> +
> + while(secno)
> + if (!test_bit(--secno, free_i->free_secmap))
> + goto check_another_zone;
> }
> - secno = left_start;
> -skip_left:
> - segno = GET_SEG_FROM_SEC(sbi, secno);
> - zoneno = GET_ZONE_FROM_SEC(sbi, secno);
>
> + /*
> + * when ALLOC_RIGHT and secno >= end_endno
> + * or ALLOC_LEFT and secno == 0, we need do the last attempt
> + * since the function should be returned with success
> + */
> + secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), 0);
> + f2fs_bug_on(sbi, secno >= MAIN_SECS(sbi));
> +
> +check_another_zone:
> /* give up on finding another zone */
> - if (!init)
> - goto got_it;
> - if (sbi->secs_per_zone == 1)
> + if (!may_again || sbi->secs_per_zone == 1)
> goto got_it;
> +
> + zoneno = GET_ZONE_FROM_SEC(sbi, secno);
> if (zoneno == old_zoneno)
> goto got_it;
> - if (dir == ALLOC_LEFT) {
> - if (!go_left && zoneno + 1 >= total_zones)
> - goto got_it;
> - if (go_left && zoneno == 0)
> +
> + /*
> + * since the following case will be likely to frequently happen,
> + * leave it here rather than put together in the following loop
> + */
> + if (dir == ALLOC_LEFT)
> + /*
> + * I'm really confused why not select
> + * zoneno * sbi->secs_per_zone - 1 in this case.
> + * Okay, leave it as the origin
> + */
> + if (!actually_go_left && zoneno + 1 >= total_zones)
> goto got_it;
> - }
> +
> for (i = 0; i < NR_CURSEG_TYPE; i++)
> - if (CURSEG_I(sbi, i)->zone == zoneno)
> - break;
> + /* the zone is in use, try another */
> + if (CURSEG_I(sbi, i)->zone == zoneno) {
> + /* try the neighbor (left or right) zone */
> + if (actually_go_left) {
> + /*
> + * since ALLOC_LEFT and no way to get free on
> + * the right side, it's safe to try the left
> + * zone and won't find the same section again.
> + */
> + if (zoneno == 0)
> + break;
> + secno = zoneno * sbi->secs_per_zone - 1;
> + } else if (zoneno + 1 >= total_zones) {
> + /* no way dir == ALLOC_LEFT at this time */
> + secno = 0;
> + } else
> + secno = (zoneno + 1) * sbi->secs_per_zone;
> +
> + /* try another zone once at most */
> + may_again = false;
> + goto try_another_section;
> + }
>
> - if (i < NR_CURSEG_TYPE) {
> - /* zone is in user, try another */
> - if (go_left)
> - hint = zoneno * sbi->secs_per_zone - 1;
> - else if (zoneno + 1 >= total_zones)
> - hint = 0;
> - else
> - hint = (zoneno + 1) * sbi->secs_per_zone;
> - init = false;
> - goto find_other_zone;
> - }
> got_it:
> + segno = GET_SEG_FROM_SEC(sbi, secno);
> +out:
> /* set it as dirty segment in free segmap */
> f2fs_bug_on(sbi, test_bit(segno, free_i->free_segmap));
> __set_inuse(sbi, segno);
> --
> 2.7.4
