Re: [RFC PATCH] mm/readahead: readahead aggressively if read drops in willneed range

Mike Snitzer
2024-01-29T17:42:41Z

On Mon, Jan 29 2024 at 12:19P -0500,
Mike Snitzer <snitzer@kernel.org> wrote:

> While I'm sure this legacy application would love to not have to
> change its code at all, I think we can all agree that we need to just
> focus on how best to advise applications that have mixed workloads
> accomplish efficient mmap+read of both sequential and random.
>
> To that end, I heard Dave clearly suggest 2 things:
>
> 1) update MADV/FADV_SEQUENTIAL to set file->f_ra.ra_pages to
> bdi->io_pages, not bdi->ra_pages * 2
>
> 2) Have the application first issue MADV_SEQUENTIAL to convey that for
> the following MADV_WILLNEED is for sequential file load (so it is
> desirable to use larger ra_pages)
>
> This overrides the default of bdi->io_pages and _should_ provide the
> required per-file duality of control for readahead, correct?

I meant "This overrides the default of bdi->ra_pages ..." ;)