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Date:	Thu, 21 Apr 2011 11:36:59 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Amir Goldstein <amir73il@...il.com>
cc:	Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org,
	tytso@....edu
Subject: Re: [PATCH] ext4: ext4_trim_fs() load buddy only when it is needed

On Tue, 19 Apr 2011, Amir Goldstein wrote:

> On Mon, Apr 18, 2011 at 7:32 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> > Currently we are loading buddy ext4_mb_load_buddy() for every block
> > group we are going through in ext4_trim_fs() in many cases just to find
> > out that there is not enough space to be bothered with. As Amir Goldstein
> > suggested we can use bb_free information directly from ext4_group_info.
> >
> > This commit removes ext4_mb_load_buddy() from ext4_trim_fs() and rather
> > get the ext4_group_info via ext4_get_group_info() and use the bb_free
> > information directly from that. This avoids unnecessary call to load
> > buddy in the case the group does not have enough free space to trim.
> > Loading buddy is now moved to ext4_trim_all_free().
> >
> > Tested by me with xfstests 251.
> >
> > Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> > ---
> >  fs/ext4/mballoc.c |   48 ++++++++++++++++++++++++++----------------------
> >  1 files changed, 26 insertions(+), 22 deletions(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index d8a16ee..776d7a8 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -4760,20 +4760,25 @@ static int ext4_trim_extent(struct super_block *sb, int start, int count,
> >  * the group buddy bitmap. This is done until whole group is scanned.
> >  */
> >  static ext4_grpblk_t
> > -ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> > -               ext4_grpblk_t start, ext4_grpblk_t max, ext4_grpblk_t minblocks)
> > +ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> > +                  ext4_grpblk_t start, ext4_grpblk_t max,
> > +                  ext4_grpblk_t minblocks)
> >  {
> >        void *bitmap;
> >        ext4_grpblk_t next, count = 0;
> > -       ext4_group_t group;
> > +       struct ext4_buddy e4b;
> >        int ret = 0;
> >
> > -       BUG_ON(e4b == NULL);
> > +       ret = ext4_mb_load_buddy(sb, group, &e4b);
> > +       if (ret) {
> > +               ext4_error(sb, "Error in loading buddy "
> > +                               "information for %u", group);
> > +               return ret;
> > +       }
> >
> > -       bitmap = e4b->bd_bitmap;
> > -       group = e4b->bd_group;
> > -       start = (e4b->bd_info->bb_first_free > start) ?
> > -               e4b->bd_info->bb_first_free : start;
> > +       bitmap = e4b.bd_bitmap;
> > +       start = (e4b.bd_info->bb_first_free > start) ?
> > +               e4b.bd_info->bb_first_free : start;
> 
> not related to the patch, but bb_first_free sound like something that
> needs lock_group
> protection. I didn't check it though.
> other than that, patch looks fine to me.

Yes, you're right. I'll send the fix in separate patch based on this
commit.

Thanks for noticing.

-Lukas

> 
> >        ext4_lock_group(sb, group);
> >
> >        while (start < max) {
> > @@ -4784,7 +4789,7 @@ ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> >
> >                if ((next - start) >= minblocks) {
> >                        ret = ext4_trim_extent(sb, start,
> > -                               next - start, group, e4b);
> > +                               next - start, group, &e4b);
> >                        if (ret < 0)
> >                                break;
> >                        count += next - start;
> > @@ -4802,10 +4807,11 @@ ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> >                        ext4_lock_group(sb, group);
> >                }
> >
> > -               if ((e4b->bd_info->bb_free - count) < minblocks)
> > +               if ((e4b.bd_info->bb_free - count) < minblocks)
> >                        break;
> >        }
> >        ext4_unlock_group(sb, group);
> > +       ext4_mb_unload_buddy(&e4b);
> >
> >        ext4_debug("trimmed %d blocks in the group %d\n",
> >                count, group);
> > @@ -4830,11 +4836,11 @@ ext4_trim_all_free(struct super_block *sb, struct ext4_buddy *e4b,
> >  */
> >  int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >  {
> > -       struct ext4_buddy e4b;
> > +       struct ext4_group_info *grp;
> >        ext4_group_t first_group, last_group;
> >        ext4_group_t group, ngroups = ext4_get_groups_count(sb);
> >        ext4_grpblk_t cnt = 0, first_block, last_block;
> > -       uint64_t start, len, minlen, trimmed;
> > +       uint64_t start, len, minlen, trimmed = 0;
> >        ext4_fsblk_t first_data_blk =
> >                        le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> >        int ret = 0;
> > @@ -4842,7 +4848,6 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >        start = range->start >> sb->s_blocksize_bits;
> >        len = range->len >> sb->s_blocksize_bits;
> >        minlen = range->minlen >> sb->s_blocksize_bits;
> > -       trimmed = 0;
> >
> >        if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
> >                return -EINVAL;
> > @@ -4863,11 +4868,12 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >                return -EINVAL;
> >
> >        for (group = first_group; group <= last_group; group++) {
> > -               ret = ext4_mb_load_buddy(sb, group, &e4b);
> > -               if (ret) {
> > -                       ext4_error(sb, "Error in loading buddy "
> > -                                       "information for %u", group);
> > -                       break;
> > +               grp = ext4_get_group_info(sb, group);
> > +               /* We only do this if the grp has never been initialized */
> > +               if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
> > +                       ret = ext4_mb_init_group(sb, group);
> > +                       if (ret)
> > +                               break;
> >                }
> >
> >                /*
> > @@ -4880,16 +4886,14 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> >                        last_block = first_block + len;
> >                len -= last_block - first_block;
> >
> > -               if (e4b.bd_info->bb_free >= minlen) {
> > -                       cnt = ext4_trim_all_free(sb, &e4b, first_block,
> > +               if (grp->bb_free >= minlen) {
> > +                       cnt = ext4_trim_all_free(sb, group, first_block,
> >                                                last_block, minlen);
> >                        if (cnt < 0) {
> >                                ret = cnt;
> > -                               ext4_mb_unload_buddy(&e4b);
> >                                break;
> >                        }
> >                }
> > -               ext4_mb_unload_buddy(&e4b);
> >                trimmed += cnt;
> >                first_block = 0;
> >        }
> > --
> > 1.7.4.2
> >
> > --
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