Mark Lord wrote:
> On 20/04/10 05:21 PM, Greg Freemyer wrote:
>> Mark,
>>
>> This is the patch implementing the new discard logic.
> ..
>> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> ..
>>> +void ext4_trim_extent(struct super_block *sb, int start, int count,
>>> + ext4_group_t group, struct ext4_buddy *e4b)
>>> +{
>>> + ext4_fsblk_t discard_block;
>>> + struct ext4_super_block *es = EXT4_SB(sb)->s_es;
>>> + struct ext4_free_extent ex;
>>> +
>>> + assert_spin_locked(ext4_group_lock_ptr(sb, group));
>>> +
>>> + ex.fe_start = start;
>>> + ex.fe_group = group;
>>> + ex.fe_len = count;
>>> +
>>> + mb_mark_used(e4b,&ex);
>>> + ext4_unlock_group(sb, group);
>>> +
>>> + discard_block = (ext4_fsblk_t)group *
>>> + EXT4_BLOCKS_PER_GROUP(sb)
>>> + + start
>>> + + le32_to_cpu(es->s_first_data_block);
>>> + trace_ext4_discard_blocks(sb,
>>> + (unsigned long long)discard_block,
>>> + count);
>>> + sb_issue_discard(sb, discard_block, count);
>>> +
>>> + ext4_lock_group(sb, group);
>>> + mb_free_blocks(NULL, e4b, start, ex.fe_len);
>>> +}
>>
>> Mark, unless I'm missing something, sb_issue_discard() above is going
>> to trigger a trim command for just the one range. I thought the
>> benchmarks you did showed that a collection of ranges needed to be
>> built, then a single trim command invoked that trimmed that group of
>> ranges.
> ..
>
> Mmm.. If that's what it is doing, then this patch set would be a
> complete disaster.
> It would take *hours* to do the initial TRIM.
>
> Lukas ?
I'm confused; do we have an interface to send a trim command for multiple ranges?
I didn't think so ... Lukas' patch is finding free ranges (above a size threshold)
to discard; it's not doing it a block at a time, if that's the concern.
-Eric
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