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

[Zhaoyang Huang]

On Thu, May 9, 2024 at 8:40 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> 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------------