Received-SPF: pass (google.com: domain of linux-kernel+bounces-196908-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Date: Fri, 31 May 2024 06:46:10 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Zhang Yi <yi.zhang@huaweicloud.com>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, djwong@kernel.org, hch@infradead.org,
	brauner@kernel.org, david@fromorbit.com, chandanbabu@kernel.org,
	jack@suse.cz, willy@infradead.org, yi.zhang@huawei.com,
	chengzhihao1@huawei.com, yukuai3@huawei.com
Subject: Re: [RFC PATCH v4 8/8] xfs: improve truncate on a realtime inode
 with huge extsize
Message-ID: <ZlnUorFO2Ptz5gcq@infradead.org>
References: <20240529095206.2568162-1-yi.zhang@huaweicloud.com>
 <20240529095206.2568162-9-yi.zhang@huaweicloud.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240529095206.2568162-9-yi.zhang@huaweicloud.com>

> +/*
> + * Decide if this file is a realtime file whose data allocation unit is larger
> + * than default.
> + */
> +static inline bool xfs_inode_has_hugertalloc(struct xfs_inode *ip)
> +{
> +	struct xfs_mount *mp = ip->i_mount;
> +
> +	return XFS_IS_REALTIME_INODE(ip) &&
> +	       mp->m_sb.sb_rextsize > XFS_B_TO_FSB(mp, XFS_DFL_RTEXTSIZE);
> +}

The default rtextsize is actually a single FSB unless we're on a striped
volume in which case it is increased.

I'll take care of removing the unused and confusing XFS_DFL_RTEXTSIZE,
but for this patch we'd need to know the trade-off of when to just
convert to unwritten.  For single-fsb rtextents we obviously don't need
any special action.  But do you see a slowdown when converting to
unwritten for small > 1 rtextsizes?  Because if not we could just
always use that code path, which would significantly simplify things
and remove yet another different to test code path.