linux-kernel - Re: [PATCH 07/10] staging: erofs: separate into init

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Date:   Thu, 22 Nov 2018 11:23:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Gao Xiang <gaoxiang25@...wei.com>
Cc:     devel@...verdev.osuosl.org, linux-erofs@...ts.ozlabs.org,
        Chao Yu <yuchao0@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>, weidu.du@...wei.com,
        Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH 07/10] staging: erofs: separate into init_once / always

On Tue, Nov 20, 2018 at 10:34:22PM +0800, Gao Xiang wrote:
> `z_erofs_vle_workgroup' is heavily generated in the decompression,
> for example, it resets 32 bytes redundantly for 64-bit platforms
> even through Z_EROFS_VLE_INLINE_PAGEVECS + Z_EROFS_CLUSTER_MAX_PAGES,
> default 4, pages are stored in `z_erofs_vle_workgroup'.
> 
> As an another example, `struct mutex' takes 72 bytes for our kirin
> 64-bit platforms, it's unnecessary to be reseted at first and
> be initialized each time.
> 
> Let's avoid filling all `z_erofs_vle_workgroup' with 0 at first
> since most fields are reinitialized to meaningful values later,
> and pagevec is no need to initialized at all.
> 
> Reviewed-by: Chao Yu <yuchao0@...wei.com>
> Signed-off-by: Gao Xiang <gaoxiang25@...wei.com>
> ---
>  drivers/staging/erofs/unzip_vle.c | 34 +++++++++++++++++++++++++++++-----
>  1 file changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/erofs/unzip_vle.c b/drivers/staging/erofs/unzip_vle.c
> index ede3383ac601..4e5843e8ee35 100644
> --- a/drivers/staging/erofs/unzip_vle.c
> +++ b/drivers/staging/erofs/unzip_vle.c
> @@ -43,12 +43,38 @@ static inline int init_unzip_workqueue(void)
>  	return z_erofs_workqueue ? 0 : -ENOMEM;
>  }
>  
> +static void init_once(void *ptr)
> +{
> +	struct z_erofs_vle_workgroup *grp = ptr;
> +	struct z_erofs_vle_work *const work =
> +		z_erofs_vle_grab_primary_work(grp);
> +	unsigned int i;
> +
> +	mutex_init(&work->lock);
> +	work->nr_pages = 0;
> +	work->vcnt = 0;
> +	for (i = 0; i < Z_EROFS_CLUSTER_MAX_PAGES; ++i)
> +		grp->compressed_pages[i] = NULL;
> +}
> +
> +static void init_always(struct z_erofs_vle_workgroup *grp)
> +{
> +	struct z_erofs_vle_work *const work =
> +		z_erofs_vle_grab_primary_work(grp);
> +
> +	atomic_set(&grp->obj.refcount, 1);
> +	grp->flags = 0;
> +
> +	DBG_BUGON(work->nr_pages);
> +	DBG_BUGON(work->vcnt);

How can these ever be triggered?  I understand the need for debugging
code when you are writing code, but at this point it shouldn't be needed
anymore, right?

thanks,

greg k-h