Re: [PATCH] mm : update ra->ra_pages if it's NOT equal to bdi->ra_pages

[Zhaoyang Huang]

On Fri, Aug 14, 2020 at 10:07 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Aug 14, 2020 at 02:43:55AM +0100, Matthew Wilcox wrote:
> > On Fri, Aug 14, 2020 at 09:30:11AM +0800, Zhaoyang Huang wrote:
> > > file->f_ra->ra_pages will remain the initialized value since it opend, which may
> > > be NOT equal to bdi->ra_pages as the latter one is updated somehow(etc,
> > > echo xxx > /sys/block/dm/queue/read_ahead_kb).So sync ra->ra_pages to the
> > > updated value when sync read.
> >
> > It still ignores the work done by shrink_readahead_size_eio()
> > and fadvise(POSIX_FADV_SEQUENTIAL).
>
> ... by the way, if you're trying to update one particular file's readahead
> state, you can just call fadvise(POSIX_FADV_NORMAL) on it.
>
> If you want to update every open file's ra_pages by writing to sysfs,
> then just no.  We don't do that.
No, What I want to fix is the file within one process's context  keeps
using the initialized value when it is opened and not sync with new
value when bdi->ra_pages changes.
>
> You haven't said what problem you're facing, so I really can't be more
> helpful.