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

[Matthew Wilcox <willy@infradead.org>]

On Fri, May 10, 2024 at 11:06:14AM +0800, Zhaoyang Huang wrote:
> On Thu, May 9, 2024 at 8:40 PM Christoph Hellwig <hch@infradead.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------------

what you could do is have blk-throttle fail bios that are tagged as
readahead if we've hit the threshold?