linux-kernel - Re: [PATCH 11/12] bdi: invert BDI_CAP_NO_ACCT

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Date:   Thu, 17 Sep 2020 11:27:42 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>, Song Liu <song@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Richard Weinberger <richard@....at>,
        Minchan Kim <minchan@...nel.org>,
        linux-mtd@...ts.infradead.org, dm-devel@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        drbd-dev@...ts.linbit.com, linux-raid@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 11/12] bdi: invert BDI_CAP_NO_ACCT_WB

On Thu 10-09-20 16:48:31, Christoph Hellwig wrote:
> Replace BDI_CAP_NO_ACCT_WB with a positive BDI_CAP_WRITEBACK_ACCT to
> make the checks more obvious.  Also remove the pointless
> bdi_cap_account_writeback wrapper that just obsfucates the check.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/fuse/inode.c             |  3 ++-
>  include/linux/backing-dev.h | 13 +++----------
>  mm/backing-dev.c            |  1 +
>  mm/page-writeback.c         |  4 ++--
>  4 files changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 17b00670fb539e..581329203d6860 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1050,7 +1050,8 @@ static int fuse_bdi_init(struct fuse_conn *fc, struct super_block *sb)
>  		return err;
>  
>  	/* fuse does it's own writeback accounting */
> -	sb->s_bdi->capabilities = BDI_CAP_NO_ACCT_WB | BDI_CAP_STRICTLIMIT;
> +	sb->s_bdi->capabilities &= ~BDI_CAP_WRITEBACK_ACCT;
> +	sb->s_bdi->capabilities |= BDI_CAP_STRICTLIMIT;
>  
>  	/*
>  	 * For a single fuse filesystem use max 1% of dirty +
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 5da4ea3dd0cc5c..b217344a2c63be 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -120,17 +120,17 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
>   *
>   * BDI_CAP_NO_ACCT_DIRTY:  Dirty pages shouldn't contribute to accounting
>   * BDI_CAP_NO_WRITEBACK:   Don't write pages back
> - * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
> + * BDI_CAP_WRITEBACK_ACCT: Automatically account writeback pages
>   * BDI_CAP_STRICTLIMIT:    Keep number of dirty pages below bdi threshold.
>   */
>  #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
>  #define BDI_CAP_NO_WRITEBACK	0x00000002
> -#define BDI_CAP_NO_ACCT_WB	0x00000004
> +#define BDI_CAP_WRITEBACK_ACCT	0x00000004
>  #define BDI_CAP_STRICTLIMIT	0x00000010
>  #define BDI_CAP_CGROUP_WRITEBACK 0x00000020
>  
>  #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
> -	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
> +	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY)
>  
>  extern struct backing_dev_info noop_backing_dev_info;
>  
> @@ -179,13 +179,6 @@ static inline bool bdi_cap_account_dirty(struct backing_dev_info *bdi)
>  	return !(bdi->capabilities & BDI_CAP_NO_ACCT_DIRTY);
>  }
>  
> -static inline bool bdi_cap_account_writeback(struct backing_dev_info *bdi)
> -{
> -	/* Paranoia: BDI_CAP_NO_WRITEBACK implies BDI_CAP_NO_ACCT_WB */
> -	return !(bdi->capabilities & (BDI_CAP_NO_ACCT_WB |
> -				      BDI_CAP_NO_WRITEBACK));
> -}
> -
>  static inline bool mapping_cap_writeback_dirty(struct address_space *mapping)
>  {
>  	return bdi_cap_writeback_dirty(inode_to_bdi(mapping->host));
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index f9a2842bd81c3d..ab0415dde5c66c 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -744,6 +744,7 @@ struct backing_dev_info *bdi_alloc(int node_id)
>  		kfree(bdi);
>  		return NULL;
>  	}
> +	bdi->capabilities = BDI_CAP_WRITEBACK_ACCT;
>  	bdi->ra_pages = VM_READAHEAD_PAGES;
>  	bdi->io_pages = VM_READAHEAD_PAGES;
>  	return bdi;
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index e9c36521461aaa..0139f9622a92da 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2738,7 +2738,7 @@ int test_clear_page_writeback(struct page *page)
>  		if (ret) {
>  			__xa_clear_mark(&mapping->i_pages, page_index(page),
>  						PAGECACHE_TAG_WRITEBACK);
> -			if (bdi_cap_account_writeback(bdi)) {
> +			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
>  				struct bdi_writeback *wb = inode_to_wb(inode);
>  
>  				dec_wb_stat(wb, WB_WRITEBACK);
> @@ -2791,7 +2791,7 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
>  						   PAGECACHE_TAG_WRITEBACK);
>  
>  			xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
> -			if (bdi_cap_account_writeback(bdi))
> +			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT)
>  				inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
>  
>  			/*
> -- 
> 2.28.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR