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

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Message-ID: <CAGWkznG4xodugVdbKZCn99UiQT5Z3oHYLhTsvOCoe_VNxUVvnw@mail.gmail.com>
Date: Fri, 10 May 2024 11:06:14 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthew Wilcox <willy@...radead.org>, Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>, 
	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, steve.kang@...soc.com
Subject: Re: [RFC PATCH 2/2] mm: introduce budgt control in readahead

On Thu, May 9, 2024 at 8:40 PM Christoph Hellwig <hch@...radead.org> wrote:
>
> > +     unsigned long budgt = inode->i_sb->s_bdev ?
> > +                     blk_throttle_budgt(inode->i_sb->s_bdev) : 0;
>
> The readahead code is used for all file systems, you can't just call
> into block layer code here.
>
ok. I would like to know any suggestions on introducing throttle
budget control into readahead which actually works as a negative
feedback path. IMO, negative feedback is a good methodology which has
been used in scheduler(EAS) and thermal control(IPA) and
memory(MGLRU). I would like to suggest to have a try on have it work
cross the boundary of memory and block layer.

vfs_read / page fault
|
readahead  <---------|
|                               |
aops->readpages    |
|                               |
block_layer------------