Re: [PATCH v3 2/3] nilfs2: add nilfs_sufile_set_suinfo to update segment usage

[Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>]

On 2014-01-27 20:07, Ryusuke Konishi wrote:
> On Mon, 27 Jan 2014 10:59:27 +0100, Andreas Rohner wrote:
>> This patch introduces the nilfs_sufile_set_suinfo function, which
>> expects an array of nilfs_suinfo_update structures and updates the
>> segment usage information accordingly.
>>
>> This is basically a helper function for the newly introduced
>> NILFS_IOCTL_SET_SUINFO ioctl.
>>
>> Signed-off-by: Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>
>> ---
>>  fs/nilfs2/sufile.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  fs/nilfs2/sufile.h |   1 +
>>  2 files changed, 130 insertions(+)
>>
>> diff --git a/fs/nilfs2/sufile.c b/fs/nilfs2/sufile.c
>> index 3127e9f..8922523 100644
>> --- a/fs/nilfs2/sufile.c
>> +++ b/fs/nilfs2/sufile.c
>> @@ -870,6 +870,135 @@ ssize_t nilfs_sufile_get_suinfo(struct inode *sufile, __u64 segnum, void *buf,
>>  }
>>  
>>  /**
>> + * nilfs_sufile_set_suinfo - sets segment usage info
>> + * @sufile: inode of segment usage file
>> + * @buf: array of suinfo_update
>> + * @supsz: byte size of suinfo_update
>> + * @nsup: size of suinfo_update array
>> + *
>> + * Description: Takes an array of nilfs_suinfo_update structs and updates
>> + * segment usage accordingly. Only the fields indicated by the sup_flags
>> + * are updated.
>> + *
>> + * Return Value: On success, 0 is returned. On error, one of the
>> + * following negative error codes is returned.
>> + *
>> + * %-EIO - I/O error.
>> + *
>> + * %-ENOMEM - Insufficient amount of memory available.
>> + *
>> + * %-EINVAL - Invalid values in input (segment number, flags or nblocks)
>> + */
>> +ssize_t nilfs_sufile_set_suinfo(struct inode *sufile, void *buf,
>> +				unsigned supsz, size_t nsup)
>> +{
>> +	struct the_nilfs *nilfs = sufile->i_sb->s_fs_info;
>> +	struct buffer_head *header_bh, *bh;
>> +	struct nilfs_suinfo_update *sup, *supend = buf + supsz * nsup;
>> +	struct nilfs_segment_usage *su;
>> +	void *kaddr;
>> +	unsigned long blkoff, prev_blkoff;
>> +	int ret = 0, ncleansegs, ndirtysegs, cleansi,
>> +			cleansu, dirtysi, dirtysu;
> 
> This indentation looks peculiar. Why not separate them into two or
> more lines?  At least, ncleansegs and ndirtysegs differ from cleansi,
> cleansu, dirtysi, dirtysu and ret.  ncleansegs and ndirtysegs sounds
> confusing since these local variables do not give a total number.
> ncleaned and ndirtied would be better.
> 
> 	int cleansi, cleansu, dirtysi, dirtysu;
> 	int ncleaned, ndirtied;
> 	int ret = 0;
> 
>> +
>> +	if (unlikely(nsup == 0))
>> +		return ret;
>> +
>> +	for (sup = buf; sup < supend; sup = (void *)sup + supsz) {
>> +		if (sup->sup_segnum >= nilfs->ns_nsegments
>> +			|| (sup->sup_flags &
>> +				(~0UL << (NILFS_SUINFO_UPDATE_FLAGS + 1)))
> 
> This looks confusing. It should be clarified as follows:
> 
> enum {
>         NILFS_SUINFO_UPDATE_LASTMOD,
>         NILFS_SUINFO_UPDATE_NBLOCKS,
>         NILFS_SUINFO_UPDATE_FLAGS,
> 	__NR_NILFS_SUINFO_FIELDS
> };
> 
> 		if (sup->sup_segnum >= nilfs->ns_nsegments ||
> 		    (sup->sup_flags & (~0UL << __NR_NILFS_SUINFO_FIELDS)) ||
> 
>> +			|| (nilfs_suinfo_update_nblocks(sup) &&
>> +				sup->sup_sui.sui_nblocks >
>> +				nilfs->ns_blocks_per_segment)
>> +			|| (nilfs_suinfo_update_flags(sup) &&
>> +				(sup->sup_sui.sui_flags &
>> +				(~0UL << (NILFS_SEGMENT_USAGE_ERROR + 1)))))
> 
> Ditto. We need to add a definition to nilfs2_fs.h.
> 
> enum {
>         NILFS_SEGMENT_USAGE_ACTIVE,
>         NILFS_SEGMENT_USAGE_DIRTY,
>         NILFS_SEGMENT_USAGE_ERROR,
> 	__NR_NILFS_SEGMENT_USAGE_FLAGS
> };
> 
> 		    (nilfs_suinfo_update_flags(sup) &&
> 		     (sup->sup_sui.sui_flags &
> 		      (~0UL << __NR_NILFS_SEGMENT_USAGE_FLAGS))))
> 
> By the way, this will dismiss the capability that userland cleaner
> programs uses the rest of su_flags for their own purpose such as GC
> optimization.  I think this (rejecting or utilizing it) should be
> carefully determined.
> 
> Any comments on this?

Hmm, I think it can't hurt to let the userland cleaner use the su_flags.
As far as I can tell, it shouldn't affect the kernel side.
nilfs_segment_usage_set_clean() would still work and
nilfs_sufile_do_scrap() overwrites the whole su_flags as well.

>> +	}
>> +
>> +	down_write(&NILFS_MDT(sufile)->mi_sem);
>> +
>> +	ret = nilfs_sufile_get_header_block(sufile, &header_bh);
>> +	if (ret < 0)
>> +		goto out_sem;
>> +
>> +	sup = buf;
>> +	blkoff = nilfs_sufile_get_blkoff(sufile, sup->sup_segnum);
>> +	ret = nilfs_mdt_get_block(sufile, blkoff, 1, NULL, &bh);
>> +	if (ret < 0)
>> +		goto out_header;
>> +
>> +	for (;;) {
>> +		kaddr = kmap_atomic(bh->b_page);
>> +		su = nilfs_sufile_block_get_segment_usage(
>> +			sufile, sup->sup_segnum, bh, kaddr);
>> +
>> +		if (nilfs_suinfo_update_lastmod(sup))
>> +			su->su_lastmod = cpu_to_le64(sup->sup_sui.sui_lastmod);
>> +
>> +		if (nilfs_suinfo_update_nblocks(sup))
>> +			su->su_nblocks = cpu_to_le32(sup->sup_sui.sui_nblocks);
>> +
>> +		if (nilfs_suinfo_update_flags(sup)) {
>> +			sup->sup_sui.sui_flags &=
>> +					~(1UL << NILFS_SEGMENT_USAGE_ACTIVE);
> 
> Your would be better off adding a comment to explain what's this.
> 
>   			/*
> 			 * Active flag is a virtual flag projected by running
> 			 * nilfs kernel code - drop it not to write it to
> 			 * disk.
> 			 */
>> +
>> +			ncleansegs = 0;
>> +			ndirtysegs = 0;
>> +			cleansi = nilfs_suinfo_clean(&sup->sup_sui);
>> +			cleansu = nilfs_segment_usage_clean(su);
>> +			dirtysi = nilfs_suinfo_dirty(&sup->sup_sui);
>> +			dirtysu = nilfs_segment_usage_dirty(su);
>> +
>> +			if (cleansi && !cleansu)
>> +				++ncleansegs;
>> +			else if (!cleansi && cleansu)
>> +				--ncleansegs;
>> +
>> +			if (dirtysi && !dirtysu)
>> +				++ndirtysegs;
>> +			else if (!dirtysi && dirtysu)
>> +				--ndirtysegs;
>> +
>> +			su->su_flags = cpu_to_le32(sup->sup_sui.sui_flags);
>> +
>> +			nilfs_sufile_mod_counter(header_bh, ncleansegs,
>> +					ndirtysegs);
> 
> Does it work for a negative value without cast of (u64) ?
> Please confirm that these counters are updated as you expected.
> 
>> +			NILFS_SUI(sufile)->ncleansegs += ncleansegs;
> 
> Ditto.  

I have tested it and it works. At least on my 64 bit architecture. It is
probably still a good idea to do an explicit cast.

How about I use s64 for ncleaned and ndirtied and move
nilfs_sufile_mod_counter outside the loop?

	s64 ncleaned = 0, ndirtied = 0;

	...

	for (;;) {
		...
	}
	mark_buffer_dirty(bh);
	brelse(bh);

 out_mark:
	if (ncleaned || ndirtied) {
		nilfs_sufile_mod_counter(header_bh, (u64)ncleaned,
				(u64)ndirtied);
		NILFS_SUI(sufile)->ncleansegs += ncleaned;
	}
	nilfs_mdt_mark_dirty(sufile);
 out_header:
	brelse(header_bh);
 out_sem:
	up_write(&NILFS_MDT(sufile)->mi_sem);
	return ret;

Best regards,
Andreas Rohner
> 
> Regards,
> Ryusuke Konishi
> 
>> +		}
>> +
>> +		kunmap_atomic(kaddr);
>> +
>> +		sup = (void *)sup + supsz;
>> +		if (sup >= supend)
>> +			break;
>> +
>> +		prev_blkoff = blkoff;
>> +		blkoff = nilfs_sufile_get_blkoff(sufile, sup->sup_segnum);
>> +		if (blkoff == prev_blkoff)
>> +			continue;
>> +
>> +		/* get different block */
>> +		mark_buffer_dirty(bh);
>> +		brelse(bh);
>> +		ret = nilfs_mdt_get_block(sufile, blkoff, 1, NULL, &bh);
>> +		if (unlikely(ret < 0))
>> +			goto out_mark;
>> +	}
>> +	mark_buffer_dirty(bh);
>> +	brelse(bh);
>> +
>> + out_mark:
>> +	nilfs_mdt_mark_dirty(sufile);
>> + out_header:
>> +	brelse(header_bh);
>> + out_sem:
>> +	up_write(&NILFS_MDT(sufile)->mi_sem);
>> +	return ret;
>> +}
>> +
>> +/**
>>   * nilfs_sufile_read - read or get sufile inode
>>   * @sb: super block instance
>>   * @susize: size of a segment usage entry
>> diff --git a/fs/nilfs2/sufile.h b/fs/nilfs2/sufile.h
>> index e84bc5b..366003c 100644
>> --- a/fs/nilfs2/sufile.h
>> +++ b/fs/nilfs2/sufile.h
>> @@ -44,6 +44,7 @@ int nilfs_sufile_set_segment_usage(struct inode *sufile, __u64 segnum,
>>  int nilfs_sufile_get_stat(struct inode *, struct nilfs_sustat *);
>>  ssize_t nilfs_sufile_get_suinfo(struct inode *, __u64, void *, unsigned,
>>  				size_t);
>> +ssize_t nilfs_sufile_set_suinfo(struct inode *, void *, unsigned , size_t);
>>  
>>  int nilfs_sufile_updatev(struct inode *, __u64 *, size_t, int, size_t *,
>>  			 void (*dofunc)(struct inode *, __u64,
>> -- 
>> 1.8.5.3
>>
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