Re: [PATCH v3 1/7] erofs: on-disk format should have explicitly assigned numbers

Re: [PATCH v3 1/7] erofs: on-disk format should have explicitly assigned numbers

[Gao Xiang]

On Fri, Aug 30, 2019 at 11:36:37AM +0800, Gao Xiang wrote:
> As Christoph claimed [1], on-disk format should have
> explicitly assigned numbers. I have to change it.
> 
> [1] https://lore.kernel.org/r/20190829095954.GB20598@infradead.org/
> Reported-by: Christoph Hellwig <hch@infradead.org>
> Reviewed-by: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>

...ignore this patchset. I will resend another incremental
patchset to address what Christoph suggested yesterday...

Thanks,
Gao Xiang

> ---
> no change
> 
>  fs/erofs/erofs_fs.h | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index afa7d45ca958..2447ad4d0920 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -52,10 +52,10 @@ struct erofs_super_block {
>   * 4~7 - reserved
>   */
>  enum {
> -	EROFS_INODE_FLAT_PLAIN,
> -	EROFS_INODE_FLAT_COMPRESSION_LEGACY,
> -	EROFS_INODE_FLAT_INLINE,
> -	EROFS_INODE_FLAT_COMPRESSION,
> +	EROFS_INODE_FLAT_PLAIN			= 0,
> +	EROFS_INODE_FLAT_COMPRESSION_LEGACY	= 1,
> +	EROFS_INODE_FLAT_INLINE			= 2,
> +	EROFS_INODE_FLAT_COMPRESSION		= 3,
>  	EROFS_INODE_LAYOUT_MAX
>  };
>  
> @@ -181,7 +181,7 @@ struct erofs_xattr_entry {
>  
>  /* available compression algorithm types */
>  enum {
> -	Z_EROFS_COMPRESSION_LZ4,
> +	Z_EROFS_COMPRESSION_LZ4	= 0,
>  	Z_EROFS_COMPRESSION_MAX
>  };
>  
> @@ -239,10 +239,10 @@ struct z_erofs_map_header {
>   *                (di_advise could be 0, 1 or 2)
>   */
>  enum {
> -	Z_EROFS_VLE_CLUSTER_TYPE_PLAIN,
> -	Z_EROFS_VLE_CLUSTER_TYPE_HEAD,
> -	Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD,
> -	Z_EROFS_VLE_CLUSTER_TYPE_RESERVED,
> +	Z_EROFS_VLE_CLUSTER_TYPE_PLAIN		= 0,
> +	Z_EROFS_VLE_CLUSTER_TYPE_HEAD		= 1,
> +	Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD	= 2,
> +	Z_EROFS_VLE_CLUSTER_TYPE_RESERVED	= 3,
>  	Z_EROFS_VLE_CLUSTER_TYPE_MAX
>  };
>  
> -- 
> 2.17.1
> 
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Re: [PATCH v3 6/7] erofs: remove all likely/unlikely annotations

[Christoph Hellwig]

On Fri, Aug 30, 2019 at 11:36:42AM +0800, Gao Xiang wrote:
> As Dan Carpenter suggested [1], I have to remove
> all erofs likely/unlikely annotations.

Do you have to remove all of them, or just those where you don't have
a particularly good reason why you think in this particular case they
might actually matter?
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Re: [PATCH v3 6/7] erofs: remove all likely/unlikely annotations

[Gao Xiang]

Hi Christoph,

On Fri, Aug 30, 2019 at 08:46:50AM -0700, Christoph Hellwig wrote:
> On Fri, Aug 30, 2019 at 11:36:42AM +0800, Gao Xiang wrote:
> > As Dan Carpenter suggested [1], I have to remove
> > all erofs likely/unlikely annotations.
> 
> Do you have to remove all of them, or just those where you don't have
> a particularly good reason why you think in this particular case they
> might actually matter?

I just added unlikely/likely for all erofs error handling paths or
rare happened cases at first... (That is all in my thought...)

I don't have some benchmark data for each unlikely/likely case (and I have
no idea "is that worth to take time to benchmark rather than do another more
useful stuffs"), so..I have to kill them all...

Thanks,
Gao Xiang


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Re: [PATCH v3 7/7] erofs: redundant assignment in __erofs_get_meta_page()

[Christoph Hellwig]

> -		err = bio_add_page(bio, page, PAGE_SIZE, 0);
> -		if (err != PAGE_SIZE) {
> +		if (bio_add_page(bio, page, PAGE_SIZE, 0) != PAGE_SIZE) {
>  			err = -EFAULT;
>  			goto err_out;
>  		}

This patch looks like an improvement.  But looking at that whole
area just makes me cringe.

Why is there __erofs_get_meta_page with the two weird booleans instead
of a single erofs_get_meta_page that gets and gfp_t for additional
flags and an unsigned int for additional bio op flags.

Why do need ioprio support to start with?  Seeing that in a new
fs look kinda odd.  Do you have benchmarks that show the difference?

That function then calls erofs_grab_bio, which tries to handle a
bio_alloc failure, except that the function will not actually fail
due the mempool backing it.  It also seems like and awfully
huge function to inline.

Why is there __submit_bio which really just obsfucates what is
going on?  Also why is __submit_bio using bio_set_op_attrs instead
of opencode it as the comment right next to it asks you to?

Also I really don't understand why you can't just use read_cache_page
or even read_cache_page_gfp instead of __erofs_get_meta_page.
That function is a whole lot of duplication of functionality shared
by a lot of other file systems.
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Re: [PATCH v3 7/7] erofs: redundant assignment in __erofs_get_meta_page()

[Gao Xiang]

Hi Christoph,

On Fri, Aug 30, 2019 at 09:28:12AM -0700, Christoph Hellwig wrote:
> > -		err = bio_add_page(bio, page, PAGE_SIZE, 0);
> > -		if (err != PAGE_SIZE) {
> > +		if (bio_add_page(bio, page, PAGE_SIZE, 0) != PAGE_SIZE) {
> >  			err = -EFAULT;
> >  			goto err_out;
> >  		}
> 
> This patch looks like an improvement.  But looking at that whole
> area just makes me cringe.

OK, I agree with you, I will improve it or just kill them all with
new iomap approach after it supports tail-end packing inline.

> 
> Why is there __erofs_get_meta_page with the two weird booleans instead
> of a single erofs_get_meta_page that gets and gfp_t for additional
> flags and an unsigned int for additional bio op flags.

I agree with you. Thanks for your suggestion.

> 
> Why do need ioprio support to start with?  Seeing that in a new
> fs look kinda odd.  Do you have benchmarks that show the difference?

I don't have some benchmark for all of these, can I just set
REQ_PRIO for all metadata? is that reasonable?
Could you kindly give some suggestion on this?

> 
> That function then calls erofs_grab_bio, which tries to handle a
> bio_alloc failure, except that the function will not actually fail
> due the mempool backing it.  It also seems like and awfully
> huge function to inline.

OK, I will simplify it. Thanks for your suggestion.

> 
> Why is there __submit_bio which really just obsfucates what is
> going on?  Also why is __submit_bio using bio_set_op_attrs instead
> of opencode it as the comment right next to it asks you to?

Originally, mainly due to backport consideration since some
of our smartphones use 3.x kernel as well...

> 
> Also I really don't understand why you can't just use read_cache_page
> or even read_cache_page_gfp instead of __erofs_get_meta_page.
> That function is a whole lot of duplication of functionality shared
> by a lot of other file systems.

OK, I have to admit, that code was originally just copied from f2fs
with some modification (maybe it's not a good example for us).

Thanks,
Gao Xiang

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Re: [PATCH v3 6/7] erofs: remove all likely/unlikely annotations

[Dan Carpenter]

On Sat, Aug 31, 2019 at 12:04:20AM +0800, Gao Xiang wrote:
> I don't have some benchmark data for each unlikely/likely case (and I have
> no idea "is that worth to take time to benchmark rather than do another more
> useful stuffs"), so..I have to kill them all...

We don't really require benchmarks, just that a reasonable person would
think it might make a difference.

regards,
dan carpenter
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