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

[Matthew Wilcox]

On Sun, Jan 28, 2024 at 10:25:22PM +0800, Ming Lei wrote:
> Since commit 6d2be915e589 ("mm/readahead.c: fix readahead failure for
> memoryless NUMA nodes and limit readahead max_pages"), ADV_WILLNEED
> only tries to readahead 512 pages, and the remained part in the advised
> range fallback on normal readahead.

Does the MAINTAINERS file mean nothing any more?

> If bdi->ra_pages is set as small, readahead will perform not efficient
> enough. Increasing read ahead may not be an option since workload may
> have mixed random and sequential I/O.

I thik there needs to be a lot more explanation than this about what's
going on before we jump to "And therefore this patch is the right
answer".

> @@ -972,6 +974,7 @@ struct file_ra_state {
>  	unsigned int ra_pages;
>  	unsigned int mmap_miss;
>  	loff_t prev_pos;
> +	struct maple_tree *need_mt;

No.  Embed the struct maple tree.  Don't allocate it.  What made you
think this was the right approach?