linux-kernel - Re: [RFC PATCH 2/2] mm: introduce budgt control in readahead

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Message-ID: <ZkRnCDasZNvFQUaY@slm.duckdns.org>
Date: Tue, 14 May 2024 21:40:56 -1000
From: Tejun Heo <tj@...nel.org>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>,
	Josef Bacik <josef@...icpanda.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, Zhaoyang Huang <huangzhaoyang@...il.com>,
	steve.kang@...soc.com
Subject: Re: [RFC PATCH 2/2] mm: introduce budgt control in readahead

Hello,

On Wed, May 15, 2024 at 09:23:50AM +0800, zhaoyang.huang wrote:
> +static unsigned long get_next_ra_size(struct readahead_control *ractl,
>  				      unsigned long max)
>  {
> +	unsigned long cur = ractl->ra->size;
> +	struct inode *inode = ractl->mapping->host;
> +	unsigned long budgt = inode->i_sb->s_bdev ?
> +			blk_throttle_budgt(inode->i_sb->s_bdev) : 0;

Technical correctness aside, I'm not convinced it's generally a good idea to
bubble up one specific IO control mechanism's detail all the way upto RA
layer. Besides what's the gain here? For continuous IO stream, whether some
RA bios are oversized or not shouldn't matter, no? Doesn't this just affect
the accuracy of the last RA IO of a finite read stream?

Thanks.

-- 
tejun