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Subject: Re: [PATCH v2 2/2] erofs: decompress in endio if possible
To:     linux-erofs@lists.ozlabs.org
Cc:     guoweichao@oppo.com, zhangshiming@oppo.com,
        linux-kernel@vger.kernel.org
References: <20210305080803.789634-1-huangjianan@oppo.com>
 <20210305080803.789634-2-huangjianan@oppo.com>
From:   Huang Jianan <huangjianan@oppo.com>
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Date:   Fri, 5 Mar 2021 16:14:56 +0800
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On 2021/3/5 16:08, Huang Jianan wrote:
> z_erofs_decompressqueue_endio may not be executed in the atomic
> context, for example, when dm-verity is turned on. In this scenario,
> data can be decompressed directly to get rid of additional kworker
> scheduling overhead. Also, it makes no sense to apply synchronous
> decompression for such case.
>
> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
> Signed-off-by: Guo Weichao <guoweichao@oppo.com>
> ---
>   fs/erofs/internal.h |  3 +++
>   fs/erofs/super.c    |  4 ++++
>   fs/erofs/zdata.c    | 13 +++++++++++--
>   3 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 67a7ec945686..b817cb85d67b 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -70,6 +70,9 @@ struct erofs_sb_info {
>   
>   	/* pseudo inode to manage cached pages */
>   	struct inode *managed_cache;
> +
> +	/* decide whether to decompress synchronously */
> +	bool readahead_sync_decompress;
>   #endif	/* CONFIG_EROFS_FS_ZIP */
>   	u32 blocks;
>   	u32 meta_blkaddr;
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index d5a6b9b888a5..77819efe9b15 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -175,6 +175,10 @@ static int erofs_read_superblock(struct super_block *sb)
>   	sbi->root_nid = le16_to_cpu(dsb->root_nid);
>   	sbi->inos = le64_to_cpu(dsb->inos);
>   
> +#ifdef CONFIG_EROFS_FS_ZIP
> +	sbi->readahead_sync_decompress = false;
> +#endif
> +
>   	sbi->build_time = le64_to_cpu(dsb->build_time);
>   	sbi->build_time_nsec = le32_to_cpu(dsb->build_time_nsec);
>   
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 6cb356c4217b..49ffc817dd9e 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -706,6 +706,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>   	goto out;
>   }
>   
> +static void z_erofs_decompressqueue_work(struct work_struct *work);
>   static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
>   				       bool sync, int bios)
>   {
> @@ -720,8 +721,14 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
>   		return;
>   	}
>   
> -	if (!atomic_add_return(bios, &io->pending_bios))
> -		queue_work(z_erofs_workqueue, &io->u.work);
> +	if (!atomic_add_return(bios, &io->pending_bios)) {
> +		if (in_atomic() || irqs_disabled()) {
> +			queue_work(z_erofs_workqueue, &io->u.work);
> +			sbi->readahead_sync_decompress = true;
> +		} else {
> +			z_erofs_decompressqueue_work(&io->u.work);
> +		}
> +	}
>   }
>   
>   static bool z_erofs_page_is_invalidated(struct page *page)
> @@ -1333,6 +1340,8 @@ static void z_erofs_readahead(struct readahead_control *rac)
>   	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
>   
>   	unsigned int nr_pages = readahead_count(rac);
> +	bool sync = (sbi->readahead_sync_decompress &&
> +			nr_pages <= sbi->ctx.max_sync_decompress_pages);
>   	bool sync = (nr_pages <= sbi->ctx.max_sync_decompress_pages);
sorry for my mistake here, i will send v3 to fix this.
>   	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
>   	struct page *page, *head = NULL;